Provided by: python-kitchen-doc_1.2.5-1_all 
NAME
kitchen - kitchen 1.2.5
Author Toshio Kuratomi
Date 19 March 2011
Version
1.0.x
We’ve all done it. In the process of writing a brand new application we’ve discovered
that we need a little bit of code that we’ve invented before. Perhaps it’s something to
handle unicode text. Perhaps it’s something to make a bit of python-2.5 code run on
python-2.4. Whatever it is, it ends up being a tiny bit of code that seems too small to
worry about pushing into its own module so it sits there, a part of your current project,
waiting to be cut and pasted into your next project. And the next. And the next. And
since that little bittybit of code proved so useful to you, it’s highly likely that it
proved useful to someone else as well. Useful enough that they’ve written it and copy and
pasted it over and over into each of their new projects.
Well, no longer! Kitchen aims to pull these small snippets of code into a few python
modules which you can import and use within your project. No more copy and paste! Now
you can let someone else maintain and release these small snippets so that you can get on
with your life.
This package forms the core of Kitchen. It contains some useful modules for using newer
python standard library modules on older python versions, text manipulation, PEP 386
versioning, and initializing gettext. With this package we’re trying to provide a few
useful features that don’t have too many dependencies outside of the python standard
library. We’ll be releasing other modules that drop into the kitchen namespace to add
other features (possibly with larger deps) as time goes on.
REQUIREMENTS
We’ve tried to keep the core kitchen module’s requirements lightweight. At the moment
kitchen only requires
python 2.4 or later
WARNING:
Kitchen-1.1.0 was the last release that supported python-2.3.x
Soft Requirements
If found, these libraries will be used to make the implementation of some part of kitchen
better in some way. If they are not present, the API that they enable will still exist
but may function in a different manner.
chardet
Used in guess_encoding() and guess_encoding_to_xml() to help guess encoding of byte
strings being converted. If not present, unknown encodings will be converted as if
they were latin1
OTHER RECOMMENDED LIBRARIES
These libraries implement commonly used functionality that everyone seems to invent.
Rather than reinvent their wheel, I simply list the things that they do well for now.
Perhaps if people can’t find them normally, I’ll add them as requirements in setup.py or
link them into kitchen’s namespace. For now, I just mention them here:
bunch Bunch is a dictionary that you can use attribute lookup as well as bracket notation
to access. Setting it apart from most homebrewed implementations is the bunchify()
function which will descend nested structures of lists and dicts, transforming the
dicts to Bunch’s.
hashlib
Python 2.5 and forward have a hashlib library that provides secure hash functions
to python. If you’re developing for python2.4 though, you can install the
standalone hashlib library and have access to the same functions.
iterutils
The python documentation for itertools has some examples of other nice iterable
functions that can be built from the itertools functions. This third-party module
creates those recipes as a module.
ordereddict
Python 2.7 and forward have a OrderedDict that provides a dict whose items are
ordered (and indexable) as well as named.
unittest2
Python 2.7 has an updated unittest library with new functions not present in the
python standard library for Python 2.6 or less. If you want to use those new
functions but need your testing framework to be compatible with older Python the
unittest2 library provides the update as an external module.
nose If you want to use a test discovery tool instead of the unittest framework,
nosetests provides a simple to use way to do that.
LICENSE
This python module is distributed under the terms of the GNU Lesser General Public License
Version 2 or later.
NOTE:
Some parts of this module are licensed under terms less restrictive than the LGPLv2+.
If you separate these files from the work as a whole you are allowed to use them under
the less restrictive licenses. The following is a list of the files that are known:
Python 2 license
_subprocess.py, test_subprocess.py, defaultdict.py, test_defaultdict.py,
_base64.py, and test_base64.py
CONTENTS
Using kitchen to write good code
Kitchen’s functions won’t automatically make you a better programmer. You have to learn
when and how to use them as well. This section of the documentation is intended to show
you some of the ways that you can apply kitchen’s functions to problems that may have
arisen in your life. The goal of this section is to give you enough information to
understand what the kitchen API can do for you and where in the KitchenAPI docs to look
for something that can help you with your next issue. Along the way, you might pick up
the knack for identifying issues with your code before you publish it. And that will make
you a better coder.
Overcoming frustration: Correctly using unicode in python2
In python-2.x, there’s two types that deal with text.
1. str is for strings of bytes. These are very similar in nature to how strings are
handled in C.
2. unicode is for strings of unicode code points.
NOTE:
Just what the dickens is “Unicode”?
One mistake that people encountering this issue for the first time make is confusing
the unicode type and the encodings of unicode stored in the str type. In python, the
unicode type stores an abstract sequence of code points. Each code point represents a
grapheme. By contrast, byte str stores a sequence of bytes which can then be mapped to
a sequence of code points. Each unicode encoding (UTF-8, UTF-7, UTF-16, UTF-32, etc)
maps different sequences of bytes to the unicode code points.
What does that mean to you as a programmer? When you’re dealing with text
manipulations (finding the number of characters in a string or cutting a string on word
boundaries) you should be dealing with unicode strings as they abstract characters in a
manner that’s appropriate for thinking of them as a sequence of letters that you will
see on a page. When dealing with I/O, reading to and from the disk, printing to a
terminal, sending something over a network link, etc, you should be dealing with byte
str as those devices are going to need to deal with concrete implementations of what
bytes represent your abstract characters.
In the python2 world many APIs use these two classes interchangeably but there are several
important APIs where only one or the other will do the right thing. When you give the
wrong type of string to an API that wants the other type, you may end up with an exception
being raised (UnicodeDecodeError or UnicodeEncodeError). However, these exceptions aren’t
always raised because python implicitly converts between types… sometimes.
Frustration #1: Inconsistent Errors
Although converting when possible seems like the right thing to do, it’s actually the
first source of frustration. A programmer can test out their program with a string like:
The quick brown fox jumped over the lazy dog and not encounter any issues. But when they
release their software into the wild, someone enters the string: I sat down for coffee at
the café and suddenly an exception is thrown. The reason? The mechanism that converts
between the two types is only able to deal with ASCII characters. Once you throw
non-ASCII characters into your strings, you have to start dealing with the conversion
manually.
So, if I manually convert everything to either byte str or unicode strings, will I be
okay? The answer is…. sometimes.
Frustration #2: Inconsistent APIs
The problem you run into when converting everything to byte str or unicode strings is that
you’ll be using someone else’s API quite often (this includes the APIs in the python
standard library) and find that the API will only accept byte str or only accept unicode
strings. Or worse, that the code will accept either when you’re dealing with strings that
consist solely of ASCII but throw an error when you give it a string that’s got non-ASCII
characters. When you encounter these APIs you first need to identify which type will work
better and then you have to convert your values to the correct type for that code. Thus
the programmer that wants to proactively fix all unicode errors in their code needs to do
two things:
1. You must keep track of what type your sequences of text are. Does my_sentence contain
unicode or str? If you don’t know that then you’re going to be in for a world of hurt.
2. Anytime you call a function you need to evaluate whether that function will do the
right thing with str or unicode values. Sending the wrong value here will lead to a
UnicodeError being thrown when the string contains non-ASCII characters.
NOTE:
There is one mitigating factor here. The python community has been standardizing on
using unicode in all its APIs. Although there are some APIs that you need to send byte
str to in order to be safe, (including things as ubiquitous as print() as we’ll see in
the next section), it’s getting easier and easier to use unicode strings with most
APIs.
Frustration #3: Inconsistent treatment of output
Alright, since the python community is moving to using unicode strings everywhere, we
might as well convert everything to unicode strings and use that by default, right?
Sounds good most of the time but there’s at least one huge caveat to be aware of. Anytime
you output text to the terminal or to a file, the text has to be converted into a byte
str. Python will try to implicitly convert from unicode to byte str… but it will throw an
exception if the bytes are non-ASCII:
>>> string = unicode(raw_input(), 'utf8')
café
>>> log = open('/var/tmp/debug.log', 'w')
>>> log.write(string)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode character u'\xe9' in position 3: ordinal not in range(128)
Okay, this is simple enough to solve: Just convert to a byte str and we’re all set:
>>> string = unicode(raw_input(), 'utf8')
café
>>> string_for_output = string.encode('utf8', 'replace')
>>> log = open('/var/tmp/debug.log', 'w')
>>> log.write(string_for_output)
>>>
So that was simple, right? Well… there’s one gotcha that makes things a bit harder to
debug sometimes. When you attempt to write non-ASCII unicode strings to a file-like
object you get a traceback every time. But what happens when you use print()? The
terminal is a file-like object so it should raise an exception right? The answer to that
is…. sometimes:
$ python
>>> print u'café'
café
No exception. Okay, we’re fine then?
We are until someone does one of the following:
• Runs the script in a different locale:
$ LC_ALL=C python
>>> # Note: if you're using a good terminal program when running in the C locale
>>> # The terminal program will prevent you from entering non-ASCII characters
>>> # python will still recognize them if you use the codepoint instead:
>>> print u'caf\xe9'
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode character u'\xe9' in position 3: ordinal not in range(128)
• Redirects output to a file:
$ cat test.py
#!/usr/bin/python -tt
# -*- coding: utf-8 -*-
print u'café'
$ ./test.py >t
Traceback (most recent call last):
File "./test.py", line 4, in <module>
print u'café'
UnicodeEncodeError: 'ascii' codec can't encode character u'\xe9' in position 3: ordinal not in range(128)
Okay, the locale thing is a pain but understandable: the C locale doesn’t understand any
characters outside of ASCII so naturally attempting to display those won’t work. Now why
does redirecting to a file cause problems? It’s because print() in python2 is treated
specially. Whereas the other file-like objects in python always convert to ASCII unless
you set them up differently, using print() to output to the terminal will use the user’s
locale to convert before sending the output to the terminal. When print() is not
outputting to the terminal (being redirected to a file, for instance), print() decides
that it doesn’t know what locale to use for that file and so it tries to convert to ASCII
instead.
So what does this mean for you, as a programmer? Unless you have the luxury of
controlling how your users use your code, you should always, always, always convert to a
byte str before outputting strings to the terminal or to a file. Python even provides you
with a facility to do just this. If you know that every unicode string you send to a
particular file-like object (for instance, stdout) should be converted to a particular
encoding you can use a codecs.StreamWriter object to convert from a unicode string into a
byte str. In particular, codecs.getwriter() will return a StreamWriter class that will
help you to wrap a file-like object for output. Using our print() example:
$ cat test.py
#!/usr/bin/python -tt
# -*- coding: utf-8 -*-
import codecs
import sys
UTF8Writer = codecs.getwriter('utf8')
sys.stdout = UTF8Writer(sys.stdout)
print u'café'
$ ./test.py >t
$ cat t
café
Frustrations #4 and #5 – The other shoes
In English, there’s a saying “waiting for the other shoe to drop”. It means that when one
event (usually bad) happens, you come to expect another event (usually worse) to come
after. In this case we have two other shoes.
Frustration #4: Now it doesn’t take byte strings?!
If you wrap sys.stdout using codecs.getwriter() and think you are now safe to print any
variable without checking its type I am afraid I must inform you that you’re not paying
enough attention to Murphy’s Law. The StreamWriter that codecs.getwriter() provides will
take unicode strings and transform them into byte str before they get to sys.stdout. The
problem is if you give it something that’s already a byte str it tries to transform that
as well. To do that it tries to turn the byte str you give it into unicode and then
transform that back into a byte str… and since it uses the ASCII codec to perform those
conversions, chances are that it’ll blow up when making them:
>>> import codecs
>>> import sys
>>> UTF8Writer = codecs.getwriter('utf8')
>>> sys.stdout = UTF8Writer(sys.stdout)
>>> print 'café'
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib64/python2.6/codecs.py", line 351, in write
data, consumed = self.encode(object, self.errors)
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 3: ordinal not in range(128)
To work around this, kitchen provides an alternate version of codecs.getwriter() that can
deal with both byte str and unicode strings. Use kitchen.text.converters.getwriter() in
place of the codecs version like this:
>>> import sys
>>> from kitchen.text.converters import getwriter
>>> UTF8Writer = getwriter('utf8')
>>> sys.stdout = UTF8Writer(sys.stdout)
>>> print u'café'
café
>>> print 'café'
café
Frustration #5: Exceptions
Okay, so we’ve gotten ourselves this far. We convert everything to unicode strings.
We’re aware that we need to convert back into byte str before we write to the terminal.
We’ve worked around the inability of the standard getwriter() to deal with both byte str
and unicode strings. Are we all set? Well, there’s at least one more gotcha: raising
exceptions with a unicode message. Take a look:
>>> class MyException(Exception):
>>> pass
>>>
>>> raise MyException(u'Cannot do this')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
__main__.MyException: Cannot do this
>>> raise MyException(u'Cannot do this while at a café')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
__main__.MyException:
>>>
No, I didn’t truncate that last line; raising exceptions really cannot handle non-ASCII
characters in a unicode string and will output an exception without the message if the
message contains them. What happens if we try to use the handy dandy getwriter() trick to
work around this?
>>> import sys
>>> from kitchen.text.converters import getwriter
>>> sys.stderr = getwriter('utf8')(sys.stderr)
>>> raise MyException(u'Cannot do this')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
__main__.MyException: Cannot do this
>>> raise MyException(u'Cannot do this while at a café')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
__main__.MyException>>>
Not only did this also fail, it even swallowed the trailing newline that’s normally
there…. So how to make this work? Transform from unicode strings to byte str manually
before outputting:
>>> from kitchen.text.converters import to_bytes
>>> raise MyException(to_bytes(u'Cannot do this while at a café'))
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
__main__.MyException: Cannot do this while at a café
>>>
WARNING:
If you use codecs.getwriter() on sys.stderr, you’ll find that raising an exception with
a byte str is broken by the default StreamWriter as well. Don’t do that or you’ll have
no way to output non-ASCII characters. If you want to use a StreamWriter to encode
other things on stderr while still having working exceptions, use
kitchen.text.converters.getwriter().
Frustration #6: Inconsistent APIs Part deux
Sometimes you do everything right in your code but other people’s code fails you. With
unicode issues this happens more often than we want. A glaring example of this is when
you get values back from a function that aren’t consistently unicode string or byte str.
An example from the python standard library is gettext. The gettext functions are used to
help translate messages that you display to users in the users’ native languages. Since
most languages contain letters outside of the ASCII range, the values that are returned
contain unicode characters. gettext provides you with ugettext() and ungettext() to
return these translations as unicode strings and gettext(), ngettext(), lgettext(), and
lngettext() to return them as encoded byte str. Unfortunately, even though they’re
documented to return only one type of string or the other, the implementation has corner
cases where the wrong type can be returned.
This means that even if you separate your unicode string and byte str correctly before you
pass your strings to a gettext function, afterwards, you might have to check that you have
the right sort of string type again.
NOTE:
kitchen.i18n provides alternate gettext translation objects that return only byte str
or only unicode string.
A few solutions
Now that we’ve identified the issues, can we define a comprehensive strategy for dealing
with them?
Convert text at the border
If you get some piece of text from a library, read from a file, etc, turn it into a
unicode string immediately. Since python is moving in the direction of unicode strings
everywhere it’s going to be easier to work with unicode strings within your code.
If your code is heavily involved with using things that are bytes, you can do the opposite
and convert all text into byte str at the border and only convert to unicode when you need
it for passing to another library or performing string operations on it.
In either case, the important thing is to pick a default type for strings and stick with
it throughout your code. When you mix the types it becomes much easier to operate on a
string with a function that can only use the other type by mistake.
NOTE:
In python3, the abstract unicode type becomes much more prominent. The type named str
is the equivalent of python2’s unicode and python3’s bytes type replaces python2’s str.
Most APIs deal in the unicode type of string with just some pieces that are low level
dealing with bytes. The implicit conversions between bytes and unicode is removed and
whenever you want to make the conversion you need to do so explicitly.
When the data needs to be treated as bytes (or unicode) use a naming convention
Sometimes you’re converting nearly all of your data to unicode strings but you have one or
two values where you have to keep byte str around. This is often the case when you need
to use the value verbatim with some external resource. For instance, filenames or key
values in a database. When you do this, use a naming convention for the data you’re
working with so you (and others reading your code later) don’t get confused about what’s
being stored in the value.
If you need both a textual string to present to the user and a byte value for an exact
match, consider keeping both versions around. You can either use two variables for this
or a dict whose key is the byte value.
NOTE:
You can use the naming convention used in kitchen as a guide for implementing your own
naming convention. It prefixes byte str variables of unknown encoding with b_ and byte
str of known encoding with the encoding name like: utf8_. If the default was to handle
str and only keep a few unicode values, those variables would be prefixed with u_.
When outputting data, convert back into bytes
When you go to send your data back outside of your program (to the filesystem, over the
network, displaying to the user, etc) turn the data back into a byte str. How you do this
will depend on the expected output format of the data. For displaying to the user, you
can use the user’s default encoding using locale.getpreferredencoding(). For entering
into a file, you’re best bet is to pick a single encoding and stick with it.
WARNING:
When using the encoding that the user has set (for instance, using
locale.getpreferredencoding(), remember that they may have their encoding set to
something that can’t display every single unicode character. That means when you
convert from unicode to a byte str you need to decide what should happen if the byte
value is not valid in the user’s encoding. For purposes of displaying messages to the
user, it’s usually okay to use the replace encoding error handler to replace the
invalid characters with a question mark or other symbol meaning the character couldn’t
be displayed.
You can use kitchen.text.converters.getwriter() to do this automatically for sys.stdout.
When creating exception messages be sure to convert to bytes manually.
When writing unittests, include non-ASCII values and both unicode and str type
Unless you know that a specific portion of your code will only deal with ASCII, be sure to
include non-ASCII values in your unittests. Including a few characters from several
different scripts is highly advised as well because some code may have special cased
accented roman characters but not know how to handle characters used in Asian alphabets.
Similarly, unless you know that that portion of your code will only be given unicode
strings or only byte str be sure to try variables of both types in your unittests. When
doing this, make sure that the variables are also non-ASCII as python’s implicit
conversion will mask problems with pure ASCII data. In many cases, it makes sense to
check what happens if byte str and unicode strings that won’t decode in the present locale
are given.
Be vigilant about spotting poor APIs
Make sure that the libraries you use return only unicode strings or byte str. Unittests
can help you spot issues here by running many variations of data through your functions
and checking that you’re still getting the types of string that you expect.
Example: Putting this all together with kitchen
The kitchen library provides a wide array of functions to help you deal with byte str and
unicode strings in your program. Here’s a short example that uses many kitchen functions
to do its work:
#!/usr/bin/python -tt
# -*- coding: utf-8 -*-
import locale
import os
import sys
import unicodedata
from kitchen.text.converters import getwriter, to_bytes, to_unicode
from kitchen.i18n import get_translation_object
if __name__ == '__main__':
# Setup gettext driven translations but use the kitchen functions so
# we don't have the mismatched bytes-unicode issues.
translations = get_translation_object('example')
# We use _() for marking strings that we operate on as unicode
# This is pretty much everything
_ = translations.ugettext
# And b_() for marking strings that we operate on as bytes.
# This is limited to exceptions
b_ = translations.lgettext
# Setup stdout
encoding = locale.getpreferredencoding()
Writer = getwriter(encoding)
sys.stdout = Writer(sys.stdout)
# Load data. Format is filename\0description
# description should be utf-8 but filename can be any legal filename
# on the filesystem
# Sample datafile.txt:
# /etc/shells\x00Shells available on caf\xc3\xa9.lan
# /var/tmp/file\xff\x00File with non-utf8 data in the filename
#
# And to create /var/tmp/file\xff (under bash or zsh) do:
# echo 'Some data' > /var/tmp/file$'\377'
datafile = open('datafile.txt', 'r')
data = {}
for line in datafile:
# We're going to keep filename as bytes because we will need the
# exact bytes to access files on a POSIX operating system.
# description, we'll immediately transform into unicode type.
b_filename, description = line.split('\0', 1)
# to_unicode defaults to decoding output from utf-8 and replacing
# any problematic bytes with the unicode replacement character
# We accept mangling of the description here knowing that our file
# format is supposed to use utf-8 in that field and that the
# description will only be displayed to the user, not used as
# a key value.
description = to_unicode(description, 'utf-8').strip()
data[b_filename] = description
datafile.close()
# We're going to add a pair of extra fields onto our data to show the
# length of the description and the filesize. We put those between
# the filename and description because we haven't checked that the
# description is free of NULLs.
datafile = open('newdatafile.txt', 'w')
# Name filename with a b_ prefix to denote byte string of unknown encoding
for b_filename in data:
# Since we have the byte representation of filename, we can read any
# filename
if os.access(b_filename, os.F_OK):
size = os.path.getsize(b_filename)
else:
size = 0
# Because the description is unicode type, we know the number of
# characters corresponds to the length of the normalized unicode
# string.
length = len(unicodedata.normalize('NFC', description))
# Print a summary to the screen
# Note that we do not let implici type conversion from str to
# unicode transform b_filename into a unicode string. That might
# fail as python would use the ASCII filename. Instead we use
# to_unicode() to explicitly transform in a way that we know will
# not traceback.
print _(u'filename: %s') % to_unicode(b_filename)
print _(u'file size: %s') % size
print _(u'desc length: %s') % length
print _(u'description: %s') % data[b_filename]
# First combine the unicode portion
line = u'%s\0%s\0%s' % (size, length, data[b_filename])
# Since the filenames are bytes, turn everything else to bytes before combining
# Turning into unicode first would be wrong as the bytes in b_filename
# might not convert
b_line = '%s\0%s\n' % (b_filename, to_bytes(line))
# Just to demonstrate that getwriter will pass bytes through fine
print b_('Wrote: %s') % b_line
datafile.write(b_line)
datafile.close()
# And just to show how to properly deal with an exception.
# Note two things about this:
# 1) We use the b_() function to translate the string. This returns a
# byte string instead of a unicode string
# 2) We're using the b_() function returned by kitchen. If we had
# used the one from gettext we would need to convert the message to
# a byte str first
message = u'Demonstrate the proper way to raise exceptions. Sincerely, \u3068\u3057\u304a'
raise Exception(b_(message))
SEE ALSO:
kitchen.text.converters
Designing Unicode Aware APIs
APIs that deal with byte str and unicode strings are difficult to get right. Here are a
few strategies with pros and cons of each.
Contents
• Designing Unicode Aware APIs
• Take either bytes or unicode, output only unicode
• Take either bytes or unicode, output the same type
• Separate functions
• Deciding whether to take str or unicode when no value is returned
• Writing to external data
• Updating data structures
• APIs to Avoid
• Returning unicode unless a conversion fails
• Ignoring values with no chance of recovery
• Raising a UnicodeException with no chance of recovery
• Knowing your data
• Do you need to operate on both bytes and unicode?
• Can you restrict the encodings?
• Single byte encodings
• Multibyte encodings
• Fixed width
• Variable Width
• ASCII compatible
• Escaped
• Other
Take either bytes or unicode, output only unicode
In this strategy, you allow the user to enter either unicode strings or byte str but what
you give back is always unicode. This strategy is easy for novice endusers to start using
immediately as they will be able to feed either type of string into the function and get
back a string that they can use in other places.
However, it does lead to the novice writing code that functions correctly when testing it
with ASCII-only data but fails when given data that contains non-ASCII characters. Worse,
if your API is not designed to be flexible, the consumer of your code won’t be able to
easily correct those problems once they find them.
Here’s a good API that uses this strategy:
from kitchen.text.converters import to_unicode
def truncate(msg, max_length, encoding='utf8', errors='replace'):
msg = to_unicode(msg, encoding, errors)
return msg[:max_length]
The call to truncate() starts with the essential parameters for performing the task. It
ends with two optional keyword arguments that define the encoding to use to transform from
a byte str to unicode and the strategy to use if undecodable bytes are encountered. The
defaults may vary depending on the use cases you have in mind. When the output is
generally going to be printed for the user to see, errors='replace' is a good default. If
you are constructing keys to a database, raisng an exception (with errors='strict') may be
a better default. In either case, having both parameters allows the person using your API
to choose how they want to handle any problems. Having the values is also a clue to them
that a conversion from byte str to unicode string is going to occur.
NOTE:
If you’re targeting python-3.1 and above, errors='surrogateescape' may be a better
default than errors='strict'. You need to be mindful of a few things when using
surrogateescape though:
• surrogateescape will cause issues if a non-ASCII compatible encoding is used (for
instance, UTF-16 and UTF-32.) That makes it unhelpful in situations where a true
general purpose method of encoding must be found. PEP 383 mentions that
surrogateescape was specifically designed with the limitations of translating using
system locales (where ASCII compatibility is generally seen as inescapable) so you
should keep that in mind.
• If you use surrogateescape to decode from bytes to unicode you will need to use an
error handler other than strict to encode as the lone surrogate that this error
handler creates makes for invalid unicode that must be handled when encoding. In
Python-3.1.2 or less, a bug in the encoder error handlers mean that you can only use
surrogateescape to encode; anything else will throw an error.
Evaluate your usages of the variables in question to see what makes sense.
Here’s a bad example of using this strategy:
from kitchen.text.converters import to_unicode
def truncate(msg, max_length):
msg = to_unicode(msg)
return msg[:max_length]
In this example, we don’t have the optional keyword arguments for encoding and errors. A
user who uses this function is more likely to miss the fact that a conversion from byte
str to unicode is going to occur. And once an error is reported, they will have to look
through their backtrace and think harder about where they want to transform their data
into unicode strings instead of having the opportunity to control how the conversion takes
place in the function itself. Note that the user does have the ability to make this work
by making the transformation to unicode themselves:
from kitchen.text.converters import to_unicode
msg = to_unicode(msg, encoding='euc_jp', errors='ignore')
new_msg = truncate(msg, 5)
Take either bytes or unicode, output the same type
This strategy is sometimes called polymorphic because the type of data that is returned is
dependent on the type of data that is received. The concept is that when you are given a
byte str to process, you return a byte str in your output. When you are given unicode
strings to process, you return unicode strings in your output.
This can work well for end users as the ones that know about the difference between the
two string types will already have transformed the strings to their desired type before
giving it to this function. The ones that don’t can remain blissfully ignorant (at least,
as far as your function is concerned) as the function does not change the type.
In cases where the encoding of the byte str is known or can be discovered based on the
input data this works well. If you can’t figure out the input encoding, however, this
strategy can fail in any of the following cases:
1. It needs to do an internal conversion between byte str and unicode string.
2. It cannot return the same data as either a unicode string or byte str.
3. You may need to deal with byte strings that are not byte-compatible with ASCII
First, a couple examples of using this strategy in a good way:
def translate(msg, table):
replacements = table.keys()
new_msg = []
for index, char in enumerate(msg):
if char in replacements:
new_msg.append(table[char])
else:
new_msg.append(char)
return ''.join(new_msg)
In this example, all of the strings that we use (except the empty string which is okay
because it doesn’t have any characters to encode) come from outside of the function. Due
to that, the user is responsible for making sure that the msg, and the keys and values in
table all match in terms of type (unicode vs str) and encoding (You can do some error
checking to make sure the user gave all the same type but you can’t do the same for the
user giving different encodings). You do not need to make changes to the string that
require you to know the encoding or type of the string; everything is a simple replacement
of one element in the array of characters in message with the character in table.
import json
from kitchen.text.converters import to_unicode, to_bytes
def first_field_from_json_data(json_string):
'''Return the first field in a json data structure.
The format of the json data is a simple list of strings.
'["one", "two", "three"]'
'''
if isinstance(json_string, unicode):
# On all python versions, json.loads() returns unicode if given
# a unicode string
return json.loads(json_string)[0]
# Byte str: figure out which encoding we're dealing with
if '\x00' not in json_data[:2]
encoding = 'utf8'
elif '\x00\x00\x00' == json_data[:3]:
encoding = 'utf-32-be'
elif '\x00\x00\x00' == json_data[1:4]:
encoding = 'utf-32-le'
elif '\x00' == json_data[0] and '\x00' == json_data[2]:
encoding = 'utf-16-be'
else:
encoding = 'utf-16-le'
data = json.loads(unicode(json_string, encoding))
return data[0].encode(encoding)
In this example the function takes either a byte str type or a unicode string that has a
list in json format and returns the first field from it as the type of the input string.
The first section of code is very straightforward; we receive a unicode string, parse it
with a function, and then return the first field from our parsed data (which our function
returned to us as json data).
The second portion that deals with byte str is not so straightforward. Before we can
parse the string we have to determine what characters the bytes in the string map to. If
we didn’t do that, we wouldn’t be able to properly find which characters are present in
the string. In order to do that we have to figure out the encoding of the byte str.
Luckily, the json specification states that all strings are unicode and encoded with one
of UTF32be, UTF32le, UTF16be, UTF16le, or UTF-8. It further defines the format such that
the first two characters are always ASCII. Each of these has a different sequence of
NULLs when they encode an ASCII character. We can use that to detect which encoding was
used to create the byte str.
Finally, we return the byte str by encoding the unicode back to a byte str.
As you can see, in this example we have to convert from byte str to unicode and back. But
we know from the json specification that byte str has to be one of a limited number of
encodings that we are able to detect. That ability makes this strategy work.
Now for some examples of using this strategy in ways that fail:
import unicodedata
def first_char(msg):
'''Return the first character in a string'''
if not isinstance(msg, unicode):
try:
msg = unicode(msg, 'utf8')
except UnicodeError:
msg = unicode(msg, 'latin1')
msg = unicodedata.normalize('NFC', msg)
return msg[0]
If you look at that code and think that there’s something fragile and prone to breaking in
the try: except: block you are correct in being suspicious. This code will fail on
multi-byte character sets that aren’t UTF-8. It can also fail on data where the sequence
of bytes is valid UTF-8 but the bytes are actually of a different encoding. The reasons
this code fails is that we don’t know what encoding the bytes are in and the code must
convert from a byte str to a unicode string in order to function.
In order to make this code robust we must know the encoding of msg. The only way to know
that is to ask the user so the API must do that:
import unicodedata
def number_of_chars(msg, encoding='utf8', errors='strict'):
if not isinstance(msg, unicode):
msg = unicode(msg, encoding, errors)
msg = unicodedata.normalize('NFC', msg)
return len(msg)
Another example of failure:
import os
def listdir(directory):
files = os.listdir(directory)
if isinstance(directory, str):
return files
# files could contain both bytes and unicode
new_files = []
for filename in files:
if not isinstance(filename, unicode):
# What to do here?
continue
new_files.appen(filename)
return new_files
This function illustrates the second failure mode. Here, not all of the possible values
can be represented as unicode without knowing more about the encoding of each of the
filenames involved. Since each filename could have a different encoding there’s a few
different options to pursue. We could make this function always return byte str since
that can accurately represent anything that could be returned. If we want to return
unicode we need to at least allow the user to specify what to do in case of an error
decoding the bytes to unicode. We can also let the user specify the encoding to use for
doing the decoding but that won’t help in all cases since not all files will be in the
same encoding (or even necessarily in any encoding):
import locale
import os
def listdir(directory, encoding=locale.getpreferredencoding(), errors='strict'):
# Note: In python-3.1+, surrogateescape may be a better default
files = os.listdir(directory)
if isinstance(directory, str):
return files
new_files = []
for filename in files:
if not isinstance(filename, unicode):
filename = unicode(filename, encoding=encoding, errors=errors)
new_files.append(filename)
return new_files
Note that although we use errors in this example as what to pass to the codec that decodes
to unicode we could also have an errors argument that decides other things to do like skip
a filename entirely, return a placeholder (Nondisplayable filename), or raise an
exception.
This leaves us with one last failure to describe:
def first_field(csv_string):
'''Return the first field in a comma separated values string.'''
try:
return csv_string[:csv_string.index(',')]
except ValueError:
return csv_string
This code looks simple enough. The hidden error here is that we are searching for a comma
character in a byte str but not all encodings will use the same sequence of bytes to
represent the comma. If you use an encoding that’s not ASCII compatible on the byte
level, then the literal comma ',' in the above code will match inappropriate bytes. Some
examples of how it can fail:
• Will find the byte representing an ASCII comma in another character
• Will find the comma but leave trailing garbage bytes on the end of the string
• Will not match the character that represents the comma in this encoding
There are two ways to solve this. You can either take the encoding value from the user or
you can take the separator value from the user. Of the two, taking the encoding is the
better option for two reasons:
1. Taking a separator argument doesn’t clearly document for the API user that the reason
they must give it is to properly match the encoding of the csv_string. They’re just as
likely to think that it’s simply a way to specify an alternate character (like “:” or
“|”) for the separator.
2. It’s possible for a variable width encoding to reuse the same byte sequence for
different characters in multiple sequences.
NOTE:
UTF-8 is resistant to this as any character’s sequence of bytes will never be a
subset of another character’s sequence of bytes.
With that in mind, here’s how to improve the API:
def first_field(csv_string, encoding='utf-8', errors='replace'):
if not isinstance(csv_string, unicode):
u_string = unicode(csv_string, encoding, errors)
is_unicode = False
else:
u_string = csv_string
try:
field = u_string[:U_string.index(u',')]
except ValueError:
return csv_string
if not is_unicode:
field = field.encode(encoding, errors)
return field
NOTE:
If you decide you’ll never encounter a variable width encoding that reuses byte
sequences you can use this code instead:
def first_field(csv_string, encoding='utf-8'):
try:
return csv_string[:csv_string.index(','.encode(encoding))]
except ValueError:
return csv_string
Separate functions
Sometimes you want to be able to take either byte str or unicode strings, perform similar
operations on either one and then return data in the same format as was given. Probably
the easiest way to do that is to have separate functions for each and adopt a naming
convention to show that one is for working with byte str and the other is for working with
unicode strings:
def translate_b(msg, table):
'''Replace values in str with other byte values like unicode.translate'''
if not isinstance(msg, str):
raise TypeError('msg must be of type str')
str_table = [chr(s) for s in xrange(0,256)]
delete_chars = []
for chr_val in (k for k in table.keys() if isinstance(k, int)):
if chr_val > 255:
raise ValueError('Keys in table must not exceed 255)')
if table[chr_val] == None:
delete_chars.append(chr(chr_val))
elif isinstance(table[chr_val], int):
if table[chr_val] > 255:
raise TypeError('table values cannot be more than 255 or less than 0')
str_table[chr_val] = chr(table[chr_val])
else:
if not isinstance(table[chr_val], str):
raise TypeError('character mapping must return integer, None or str')
str_table[chr_val] = table[chr_val]
str_table = ''.join(str_table)
delete_chars = ''.join(delete_chars)
return msg.translate(str_table, delete_chars)
def translate(msg, table):
'''Replace values in a unicode string with other values'''
if not isinstance(msg, unicode):
raise TypeError('msg must be of type unicode')
return msg.translate(table)
There’s several things that we have to do in this API:
• Because the function names might not be enough of a clue to the user of the functions of
the value types that are expected, we have to check that the types are correct.
• We keep the behaviour of the two functions as close to the same as possible, just with
byte str and unicode strings substituted for each other.
Deciding whether to take str or unicode when no value is returned
Not all functions have a return value. Sometimes a function is there to interact with
something external to python, for instance, writing a file out to disk or a method exists
to update the internal state of a data structure. One of the main questions with these
APIs is whether to take byte str, unicode string, or both. The answer depends on your use
case but I’ll give some examples here.
Writing to external data
When your information is going to an external data source like writing to a file you need
to decide whether to take in unicode strings or byte str. Remember that most external
data sources are not going to be dealing with unicode directly. Instead, they’re going to
be dealing with a sequence of bytes that may be interpreted as unicode. With that in
mind, you either need to have the user give you a byte str or convert to a byte str inside
the function.
Next you need to think about the type of data that you’re receiving. If it’s textual
data, (for instance, this is a chat client and the user is typing messages that they
expect to be read by another person) it probably makes sense to take in unicode strings
and do the conversion inside your function. On the other hand, if this is a lower level
function that’s passing data into a network socket, it probably should be taking byte str
instead.
Just as noted in the API notes above, you should specify an encoding and errors argument
if you need to transform from unicode string to byte str and you are unable to guess the
encoding from the data itself.
Updating data structures
Sometimes your API is just going to update a data structure and not immediately output
that data anywhere. Just as when writing external data, you should think about both what
your function is going to do with the data eventually and what the caller of your function
is thinking that they’re giving you. Most of the time, you’ll want to take unicode
strings and enter them into the data structure as unicode when the data is textual in
nature. You’ll want to take byte str and enter them into the data structure as byte str
when the data is not text. Use a naming convention so the user knows what’s expected.
APIs to Avoid
There are a few APIs that are just wrong. If you catch yourself making an API that does
one of these things, change it before anyone sees your code.
Returning unicode unless a conversion fails
This type of API usually deals with byte str at some point and converts it to unicode
because it’s usually thought to be text. However, there are times when the bytes fail to
convert to a unicode string. When that happens, this API returns the raw byte str instead
of a unicode string. One example of this is present in the python standard library:
python2’s os.listdir():
>>> import os
>>> import locale
>>> locale.getpreferredencoding()
'UTF-8'
>>> os.mkdir('/tmp/mine')
>>> os.chdir('/tmp/mine')
>>> open('nonsense_char_\xff', 'w').close()
>>> open('all_ascii', 'w').close()
>>> os.listdir(u'.')
[u'all_ascii', 'nonsense_char_\xff']
The problem with APIs like this is that they cause failures that are hard to debug because
they don’t happen where the variables are set. For instance, let’s say you take the
filenames from os.listdir() and give it to this function:
def normalize_filename(filename):
'''Change spaces and dashes into underscores'''
return filename.translate({ord(u' '):u'_', ord(u' '):u'_'})
When you test this, you use filenames that all are decodable in your preferred encoding
and everything seems to work. But when this code is run on a machine that has filenames
in multiple encodings the filenames returned by os.listdir() suddenly include byte str.
And byte str has a different string.translate() function that takes different values. So
the code raises an exception where it’s not immediately obvious that os.listdir() is at
fault.
Ignoring values with no chance of recovery
An early version of python3 attempted to fix the os.listdir() problem pointed out in the
last section by returning all values that were decodable to unicode and omitting the
filenames that were not. This lead to the following output:
>>> import os
>>> import locale
>>> locale.getpreferredencoding()
'UTF-8'
>>> os.mkdir('/tmp/mine')
>>> os.chdir('/tmp/mine')
>>> open(b'nonsense_char_\xff', 'w').close()
>>> open('all_ascii', 'w').close()
>>> os.listdir('.')
['all_ascii']
The issue with this type of code is that it is silently doing something surprising. The
caller expects to get a full list of files back from os.listdir(). Instead, it silently
ignores some of the files, returning only a subset. This leads to code that doesn’t do
what is expected that may go unnoticed until the code is in production and someone notices
that something important is being missed.
Raising a UnicodeException with no chance of recovery
Believe it or not, a few libraries exist that make it impossible to deal with unicode text
without raising a UnicodeError. What seems to occur in these libraries is that the
library has functions that expect to receive a unicode string. However, internally, those
functions call other functions that expect to receive a byte str. The programmer of the
API was smart enough to convert from a unicode string to a byte str but they did not give
the user the chance to specify the encodings to use or how to deal with errors. This
results in exceptions when the user passes in a byte str because the initial function
wants a unicode string and exceptions when the user passes in a unicode string because the
function can’t convert the string to bytes in the encoding that it’s selected.
Do not put the user in the position of not being able to use your API without raising a
UnicodeError with certain values. If you can only safely take unicode strings, document
that byte str is not allowed and vice versa. If you have to convert internally, make sure
to give the caller of your function parameters to control the encoding and how to treat
errors that may occur during the encoding/decoding process. If your code will raise a
UnicodeError with non-ASCII values no matter what, you should probably rethink your API.
Knowing your data
If you’ve read all the way down to this section without skipping you’ve seen several
admonitions about the type of data you are processing affecting the viability of the
various API choices.
Here’s a few things to consider in your data:
Do you need to operate on both bytes and unicode?
Much of the data in libraries, programs, and the general environment outside of python is
written where strings are sequences of bytes. So when we interact with data that comes
from outside of python or data that is about to leave python it may make sense to only
operate on the data as a byte str. There’s two times when this may make sense:
1. The user is intended to hand the data to the function and then the function takes care
of sending the data outside of python (to the filesystem, over the network, etc).
2. The data is not representable as text. For instance, writing a binary file format.
Even when your code is operating in this area you still need to think a little more about
your data. For instance, it might make sense for the person using your API to pass in
unicode strings and let the function convert that into the byte str that it then sends
over the wire.
There are also times when it might make sense to operate only on unicode strings. unicode
represents text so anytime that you are working on textual data that isn’t going to leave
python it has the potential to be a unicode-only API. However, there’s two things that
you should consider when designing a unicode-only API:
1. As your API gains popularity, people are going to use your API in places that you may
not have thought of. Corner cases in these other places may mean that processing bytes
is desirable.
2. In python2, byte str and unicode are often used interchangeably with each other. That
means that people programming against your API may have received str from some other
API and it would be most convenient for their code if your API accepted it.
NOTE:
In python3, the separation between the text type and the byte type are more clear. So
in python3, there’s less need to have all APIs take both unicode and bytes.
Can you restrict the encodings?
If you determine that you have to deal with byte str you should realize that not all
encodings are created equal. Each has different properties that may make it possible to
provide a simpler API provided that you can reasonably tell the users of your API that
they cannot use certain classes of encodings.
As one example, if you are required to find a comma (,) in a byte str you have different
choices based on what encodings are allowed. If you can reasonably restrict your API
users to only giving ASCII compatible encodings you can do this simply by searching for
the literal comma character because that character will be represented by the same byte
sequence in all ASCII compatible encodings.
The following are some classes of encodings to be aware of as you decide how generic your
code needs to be.
Single byte encodings
Single byte encodings can only represent 256 total characters. They encode the code
points for a character to the equivalent number in a single byte.
Most single byte encodings are ASCII compatible. ASCII compatible encodings are the most
likely to be usable without changes to code so this is good news. A notable exception to
this is the EBDIC family of encodings.
Multibyte encodings
Multibyte encodings use more than one byte to encode some characters.
Fixed width
Fixed width encodings have a set number of bytes to represent all of the characters in the
character set. UTF-32 is an example of a fixed width encoding that uses four bytes per
character and can express every unicode characters. There are a number of problems with
writing APIs that need to operate on fixed width, multibyte characters. To go back to our
earlier example of finding a comma in a string, we have to realize that even in UTF-32
where the code point for ASCII characters is the same as in ASCII, the byte sequence for
them is different. So you cannot search for the literal byte character as it may pick up
false positives and may break a byte sequence in an odd place.
Variable Width
ASCII compatible
UTF-8 and the EUC family of encodings are examples of ASCII compatible multi-byte
encodings. They achieve this by adhering to two principles:
• All of the ASCII characters are represented by the byte that they are in the ASCII
encoding.
• None of the ASCII byte sequences are reused in any other byte sequence for a different
character.
Escaped
Some multibyte encodings work by using only bytes from the ASCII encoding but when a
particular sequence of those byes is found, they are interpreted as meaning something
other than their ASCII values. UTF-7 is one such encoding that can encode all of the
unicode code points. For instance, here’s a some Japanese characters encoded as UTF-7:
>>> a = u'\u304f\u3089\u3068\u307f'
>>> print a
くらとみ
>>> print a.encode('utf-7')
+ME8wiTBoMH8-
These encodings can be used when you need to encode unicode data that may contain
non-ASCII characters for inclusion in an ASCII only transport medium or file.
However, they are not ASCII compatible in the sense that we used earlier as the bytes that
represent a ASCII character are being reused as part of other characters. If you were to
search for a literal plus sign in this encoded string, you would run across many false
positives, for instance.
Other
There are many other popular variable width encodings, for instance UTF-16 and shift-JIS.
Many of these are not ASCII compatible so you cannot search for a literal ASCII character
without danger of false positives or false negatives.
Kitchen API
Kitchen is structured as a collection of modules. In its current configuration, Kitchen
ships with the following modules. Other addon modules that may drag in more dependencies
can be found on the project webpage
Kitchen.i18n Module
I18N is an important piece of any modern program. Unfortunately, setting up i18n in your
program is often a confusing process. The functions provided here aim to make the
programming side of that a little easier.
Most projects will be able to do something like this when they startup:
# myprogram/__init__.py:
import os
import sys
from kitchen.i18n import easy_gettext_setup
_, N_ = easy_gettext_setup('myprogram', localedirs=(
os.path.join(os.path.realpath(os.path.dirname(__file__)), 'locale'),
os.path.join(sys.prefix, 'lib', 'locale')
))
Then, in other files that have strings that need translating:
# myprogram/commands.py:
from myprogram import _, N_
def print_usage():
print _(u"""available commands are:
--help Display help
--version Display version of this program
--bake-me-a-cake as fast as you can
""")
def print_invitations(age):
print _('Please come to my party.')
print N_('I will be turning %(age)s year old',
'I will be turning %(age)s years old', age) % {'age': age}
See the documentation of easy_gettext_setup() and get_translation_object() for more
details.
SEE ALSO:
gettext
for details of how the python gettext facilities work
babel The babel module for in depth information on gettext, message catalogs, and
translating your app. babel provides some nice features for i18n on top of
gettext
Functions
easy_gettext_setup() should satisfy the needs of most users. get_translation_object() is
designed to ease the way for anyone that needs more control.
kitchen.i18n.easy_gettext_setup(domain, localedirs=(), use_unicode=True)
Setup translation functions for an application
Parameters
• domain – Name of the message domain. This should be a unique name that
can be used to lookup the message catalog for this app.
• localedirs – Iterator of directories to look for message catalogs under.
The first directory to exist is used regardless of whether messages for
this domain are present. If none of the directories exist, fallback on
sys.prefix + /share/locale Default: No directories to search so we just
use the fallback.
• use_unicode – If True return the gettext functions for unicode strings
else return the functions for byte str for the translations. Default is
True.
Returns
tuple of the gettext function and gettext function for plurals
Setting up gettext can be a little tricky because of lack of documentation. This
function will setup gettext using the Class-based API for you. For the simple
case, you can use the default arguments and call it like this:
_, N_ = easy_gettext_setup()
This will get you two functions, _() and N_() that you can use to mark strings in
your code for translation. _() is used to mark strings that don’t need to worry
about plural forms no matter what the value of the variable is. N_() is used to
mark strings that do need to have a different form if a variable in the string is
plural.
SEE ALSO:
api-i18n
This module’s documentation has examples of using _() and N_()
get_translation_object()
for information on how to use localedirs to get the proper message
catalogs both when in development and when installed to FHS compliant
directories on Linux.
NOTE:
The gettext functions returned from this function should be superior to the ones
returned from gettext. The traits that make them better are described in the
DummyTranslations and NewGNUTranslations documentation.
Changed in version kitchen-0.2.4: ; API kitchen.i18n 2.0.0 Changed
easy_gettext_setup() to return the lgettext functions instead of gettext functions
when use_unicode=False.
kitchen.i18n.get_translation_object(domain, localedirs=(), languages=None, class_=None,
fallback=True, codeset=None, python2_api=True)
Get a translation object bound to the message catalogs
Parameters
• domain – Name of the message domain. This should be a unique name that
can be used to lookup the message catalog for this app or library.
• localedirs – Iterator of directories to look for message catalogs under.
The directories are searched in order for message catalogs. For each of
the directories searched, we check for message catalogs in any language
specified in:attr:languages. The message catalogs are used to create the
Translation object that we return. The Translation object will attempt to
lookup the msgid in the first catalog that we found. If it’s not in
there, it will go through each subsequent catalog looking for a match.
For this reason, the order in which you specify the localedirs may be
important. If no message catalogs are found, either return a
DummyTranslations object or raise an IOError depending on the value of
fallback. Rhe default localedir from gettext which is
os.path.join(sys.prefix, 'share', 'locale') on Unix is implicitly appended
to the localedirs, making it the last directory searched.
• languages –
Iterator of language codes to check for message catalogs. If unspecified,
the user’s locale settings will be used.
SEE ALSO:
gettext.find() for information on what environment variables are used.
• class – The class to use to extract translations from the message
catalogs. Defaults to NewGNUTranslations.
• fallback – If set to data:False, raise an IOError if no message catalogs
are found. If True, the default, return a DummyTranslations object.
• codeset – Set the character encoding to use when returning byte str
objects. This is equivalent to calling output_charset() on the
Translations object that is returned from this function.
• python2_api – When data:True (default), return Translation objects that
use the python2 gettext api (gettext() and lgettext() return byte str.
ugettext() exists and returns unicode strings). When False, return
Translation objects that use the python3 gettext api (gettext returns
unicode strings and lgettext returns byte str. ugettext does not exist.)
Returns
Translation object to get gettext methods from
If you need more flexibility than easy_gettext_setup(), use this function. It sets
up a gettext Translation object and returns it to you. Then you can access any of
the methods of the object that you need directly. For instance, if you
specifically need to access lgettext():
translations = get_translation_object('foo')
translations.lgettext('My Message')
This function is similar to the python standard library gettext.translation() but
makes it better in two ways
1.
It returns NewGNUTranslations or DummyTranslations
objects by default. These are superior to the gettext.GNUTranslations
and gettext.NullTranslations objects because they are consistent in the
string type they return and they fix several issues that can cause the
python standard library objects to throw UnicodeError.
2.
This function takes multiple directories to search for
message catalogs.
The latter is important when setting up gettext in a portable manner. There is not
a common directory for translations across operating systems so one needs to look
in multiple directories for the translations. get_translation_object() is able to
handle that if you give it a list of directories to search for catalogs:
translations = get_translation_object('foo', localedirs=(
os.path.join(os.path.realpath(os.path.dirname(__file__)), 'locale'),
os.path.join(sys.prefix, 'lib', 'locale')))
This will search for several different directories:
1. A directory named locale in the same directory as the module that called
get_translation_object(),
2. In /usr/lib/locale
3. In /usr/share/locale (the fallback directory)
This allows gettext to work on Windows and in development (where the message
catalogs are typically in the toplevel module directory) and also when installed
under Linux (where the message catalogs are installed in /usr/share/locale). You
(or the system packager) just need to install the message catalogs in
/usr/share/locale and remove the locale directory from the module to make this
work. ie:
In development:
~/foo # Toplevel module directory
~/foo/__init__.py
~/foo/locale # With message catalogs below here:
~/foo/locale/es/LC_MESSAGES/foo.mo
Installed on Linux:
/usr/lib/python2.7/site-packages/foo
/usr/lib/python2.7/site-packages/foo/__init__.py
/usr/share/locale/ # With message catalogs below here:
/usr/share/locale/es/LC_MESSAGES/foo.mo
NOTE:
This function will setup Translation objects that attempt to lookup msgids in
all of the found message catalogs. This means if you have several versions of
the message catalogs installed in different directories that the function
searches, you need to make sure that localedirs specifies the directories so
that newer message catalogs are searched first. It also means that if a newer
catalog does not contain a translation for a msgid but an older one that’s in
localedirs does, the translation from that older catalog will be returned.
Changed in version kitchen-1.1.0: ; API kitchen.i18n 2.1.0 Add more parameters to
get_translation_object() so it can more easily be used as a replacement for
gettext.translation(). Also change the way we use localedirs. We cycle through
them until we find a suitable locale file rather than simply cycling through until
we find a directory that exists. The new code is based heavily on the python
standard library gettext.translation() function.
Changed in version kitchen-1.2.0: ; API kitchen.i18n 2.2.0 Add python2_api
parameter
Translation Objects
The standard translation objects from the gettext module suffer from several problems:
• They can throw UnicodeError
• They can’t find translations for non-ASCII byte str messages
• They may return either unicode string or byte str from the same function even though the
functions say they will only return unicode or only return byte str.
DummyTranslations and NewGNUTranslations were written to fix these issues.
class kitchen.i18n.DummyTranslations(fp=None, python2_api=True)
Safer version of gettext.NullTranslations
This Translations class doesn’t translate the strings and is intended to be used as
a fallback when there were errors setting up a real Translations object. It’s
safer than gettext.NullTranslations in its handling of byte str vs unicode strings.
Unlike NullTranslations, this Translation class will never throw a UnicodeError.
The code that you have around a call to DummyTranslations might throw a
UnicodeError but at least that will be in code you control and can fix. Also,
unlike NullTranslations all of this Translation object’s methods guarantee to
return byte str except for ugettext() and ungettext() which guarantee to return
unicode strings.
When byte str are returned, the strings will be encoded according to this
algorithm:
1. If a fallback has been added, the fallback will be called first. You’ll need to
consult the fallback to see whether it performs any encoding changes.
2. If a byte str was given, the same byte str will be returned.
3. If a unicode string was given and set_output_charset() has been called then we
encode the string using the output_charset
4. If a unicode string was given and this is gettext() or ngettext() and _charset
was set output in that charset.
5. If a unicode string was given and this is gettext() or ngettext() we encode it
using ‘utf-8’.
6. If a unicode string was given and this is lgettext() or lngettext() we encode
using the value of locale.getpreferredencoding()
For ugettext() and ungettext(), we go through the same set of steps with the
following differences:
• We transform byte str into unicode strings for these methods.
• The encoding used to decode the byte str is taken from input_charset if it’s set,
otherwise we decode using UTF-8.
input_charset
is an extension to the python standard library gettext that specifies what
charset a message is encoded in when decoding a message to unicode. This is
used for two purposes:
1. If the message string is a byte str, this is used to decode the string to a
unicode string before looking it up in the message catalog.
2. In ugettext() and ungettext() methods, if a byte str is given as the message and
is untranslated this is used as the encoding when decoding to unicode. This is
different from _charset which may be set when a message catalog is loaded
because input_charset is used to describe an encoding used in a python source
file while _charset describes the encoding used in the message catalog file.
Any characters that aren’t able to be transformed from a byte str to unicode string
or vice versa will be replaced with a replacement character (ie: u'�' in unicode
based encodings, '?' in other ASCII compatible encodings).
SEE ALSO:
gettext.NullTranslations
For information about what methods are available and what they do.
Changed in version kitchen-1.1.0: ; API kitchen.i18n 2.1.0 * Although we had
adapted gettext(), ngettext(),
lgettext(), and lngettext() to always return byte
str, we hadn’t forced those byte str to always be
in a specified charset. We now make sure that gettext() and
ngettext() return byte str encoded using
output_charset if set, otherwise charset and if
neither of those, UTF-8. With lgettext() and
lngettext() output_charset if set, otherwise
locale.getpreferredencoding(). * Make setting input_charset and output_charset
also
set those attributes on any fallback translation objects.
Changed in version kitchen-1.2.0: ; API kitchen.i18n 2.2.0 Add python2_api
parameter to __init__()
set_output_charset(charset)
Set the output charset
This serves two purposes. The normal
gettext.NullTranslations.set_output_charset() does not set the output on
fallback objects. On python-2.3, gettext.NullTranslations objects don’t
contain this method.
class kitchen.i18n.NewGNUTranslations(fp=None, python2_api=True)
Safer version of gettext.GNUTranslations
gettext.GNUTranslations suffers from two problems that this class fixes.
1. gettext.GNUTranslations can throw a UnicodeError in
gettext.GNUTranslations.ugettext() if the message being translated has non-ASCII
characters and there is no translation for it.
2. gettext.GNUTranslations can return byte str from
gettext.GNUTranslations.ugettext() and unicode strings from the other gettext()
methods if the message being translated is the wrong type
When byte str are returned, the strings will be encoded according to this
algorithm:
1. If a fallback has been added, the fallback will be called first. You’ll need to
consult the fallback to see whether it performs any encoding changes.
2. If a byte str was given, the same byte str will be returned.
3. If a unicode string was given and set_output_charset() has been called then we
encode the string using the output_charset
4. If a unicode string was given and this is gettext() or ngettext() and a charset
was detected when parsing the message catalog, output in that charset.
5. If a unicode string was given and this is gettext() or ngettext() we encode it
using UTF-8.
6. If a unicode string was given and this is lgettext() or lngettext() we encode
using the value of locale.getpreferredencoding()
For ugettext() and ungettext(), we go through the same set of steps with the
following differences:
• We transform byte str into unicode strings for these methods.
• The encoding used to decode the byte str is taken from input_charset if it’s set,
otherwise we decode using UTF-8
input_charset
an extension to the python standard library gettext that specifies what
charset a message is encoded in when decoding a message to unicode. This is
used for two purposes:
1. If the message string is a byte str, this is used to decode the string to a
unicode string before looking it up in the message catalog.
2. In ugettext() and ungettext() methods, if a byte str is given as the message and
is untranslated his is used as the encoding when decoding to unicode. This is
different from the _charset parameter that may be set when a message catalog is
loaded because input_charset is used to describe an encoding used in a python
source file while _charset describes the encoding used in the message catalog
file.
Any characters that aren’t able to be transformed from a byte str to unicode string
or vice versa will be replaced with a replacement character (ie: u'�' in unicode
based encodings, '?' in other ASCII compatible encodings).
SEE ALSO:
gettext.GNUTranslations.gettext
For information about what methods this class has and what they do
Changed in version kitchen-1.1.0: ; API kitchen.i18n 2.1.0 Although we had adapted
gettext(), ngettext(), lgettext(), and lngettext() to always return byte str, we
hadn’t forced those byte str to always be in a specified charset. We now make sure
that gettext() and ngettext() return byte str encoded using output_charset if set,
otherwise charset and if neither of those, UTF-8. With lgettext() and lngettext()
output_charset if set, otherwise locale.getpreferredencoding().
Kitchen.text: unicode and utf8 and xml oh my!
The kitchen.text module contains functions that deal with text manipulation.
Kitchen.text.converters
Functions to handle conversion of byte str and unicode strings.
Changed in version kitchen: 0.2a2 ; API kitchen.text 2.0.0 Added getwriter()
Changed in version kitchen: 0.2.2 ; API kitchen.text 2.1.0 Added exception_to_unicode(),
exception_to_bytes(), EXCEPTION_CONVERTERS, and BYTE_EXCEPTION_CONVERTERS
Changed in version kitchen: 1.0.1 ; API kitchen.text 2.1.1 Deprecated
BYTE_EXCEPTION_CONVERTERS as we’ve simplified exception_to_unicode() and
exception_to_bytes() to make it unnecessary
Byte Strings and Unicode in Python2
Python2 has two string types, str and unicode. unicode represents an abstract sequence of
text characters. It can hold any character that is present in the unicode standard. str
can hold any byte of data. The operating system and python work together to display these
bytes as characters in many cases but you should always keep in mind that the information
is really a sequence of bytes, not a sequence of characters. In python2 these types are
interchangeable a large amount of the time. They are one of the few pairs of types that
automatically convert when used in equality:
>>> # string is converted to unicode and then compared
>>> "I am a string" == u"I am a string"
True
>>> # Other types, like int, don't have this special treatment
>>> 5 == "5"
False
However, this automatic conversion tends to lull people into a false sense of security.
As long as you’re dealing with ASCII characters the automatic conversion will save you
from seeing any differences. Once you start using characters that are not in ASCII, you
will start getting UnicodeError and UnicodeWarning as the automatic conversions between
the types fail:
>>> "I am an ñ" == u"I am an ñ"
__main__:1: UnicodeWarning: Unicode equal comparison failed to convert both arguments to Unicode - interpreting them as being unequal
False
Why do these conversions fail? The reason is that the python2 unicode type represents an
abstract sequence of unicode text known as code points. str, on the other hand, really
represents a sequence of bytes. Those bytes are converted by your operating system to
appear as characters on your screen using a particular encoding (usually with a default
defined by the operating system and customizable by the individual user.) Although ASCII
characters are fairly standard in what bytes represent each character, the bytes outside
of the ASCII range are not. In general, each encoding will map a different character to a
particular byte. Newer encodings map individual characters to multiple bytes (which the
older encodings will instead treat as multiple characters). In the face of these
differences, python refuses to guess at an encoding and instead issues a warning or
exception and refuses to convert.
SEE ALSO:
overcoming-frustration
For a longer introduction on this subject.
Strategy for Explicit Conversion
So what is the best method of dealing with this weltering babble of incoherent encodings?
The basic strategy is to explicitly turn everything into unicode when it first enters your
program. Then, when you send it to output, you can transform the unicode back into bytes.
Doing this allows you to control the encodings that are used and avoid getting tracebacks
due to UnicodeError. Using the functions defined in this module, that looks something like
this:
>>> from kitchen.text.converters import to_unicode, to_bytes
>>> name = raw_input('Enter your name: ')
Enter your name: Toshio くらとみ
>>> name
'Toshio \xe3\x81\x8f\xe3\x82\x89\xe3\x81\xa8\xe3\x81\xbf'
>>> type(name)
<type 'str'>
>>> unicode_name = to_unicode(name)
>>> type(unicode_name)
<type 'unicode'>
>>> unicode_name
u'Toshio \u304f\u3089\u3068\u307f'
>>> # Do a lot of other things before needing to save/output again:
>>> output = open('datafile', 'w')
>>> output.write(to_bytes(u'Name: %s\\n' % unicode_name))
A few notes:
Looking at line 6, you’ll notice that the input we took from the user was a byte str. In
general, anytime we’re getting a value from outside of python (The filesystem, reading
data from the network, interacting with an external command, reading values from the
environment) we are interacting with something that will want to give us a byte str. Some
python standard library modules and third party libraries will automatically attempt to
convert a byte str to unicode strings for you. This is both a boon and a curse. If the
library can guess correctly about the encoding that the data is in, it will return unicode
objects to you without you having to convert. However, if it can’t guess correctly, you
may end up with one of several problems:
UnicodeError
The library attempted to decode a byte str into a unicode, string failed, and
raises an exception.
Garbled data
If the library returns the data after decoding it with the wrong encoding, the
characters you see in the unicode string won’t be the ones that you expect.
A byte str instead of unicode string
Some libraries will return a unicode string when they’re able to decode the data
and a byte str when they can’t. This is generally the hardest problem to debug
when it occurs. Avoid it in your own code and try to avoid or open bugs against
upstreams that do this. See DesigningUnicodeAwareAPIs for strategies to do this
properly.
On line 8, we convert from a byte str to a unicode string. to_unicode() does this for us.
It has some error handling and sane defaults that make this a nicer function to use than
calling str.decode() directly:
• Instead of defaulting to the ASCII encoding which fails with all but the simple American
English characters, it defaults to UTF-8.
• Instead of raising an error if it cannot decode a value, it will replace the value with
the unicode “Replacement character” symbol (�).
• If you happen to call this method with something that is not a str or unicode, it will
return an empty unicode string.
All three of these can be overridden using different keyword arguments to the function.
See the to_unicode() documentation for more information.
On line 15 we push the data back out to a file. Two things you should note here:
1. We deal with the strings as unicode until the last instant. The string format that
we’re using is unicode and the variable also holds unicode. People sometimes get into
trouble when they mix a byte str format with a variable that holds a unicode string (or
vice versa) at this stage.
2. to_bytes(), does the reverse of to_unicode(). In this case, we’re using the default
values which turn unicode into a byte str using UTF-8. Any errors are replaced with a
� and sending nonstring objects yield empty unicode strings. Just like to_unicode(),
you can look at the documentation for to_bytes() to find out how to override any of
these defaults.
When to use an alternate strategy
The default strategy of decoding to unicode strings when you take data in and encoding to
a byte str when you send the data back out works great for most problems but there are a
few times when you shouldn’t:
• The values aren’t meant to be read as text
• The values need to be byte-for-byte when you send them back out – for instance if they
are database keys or filenames.
• You are transferring the data between several libraries that all expect byte str.
In each of these instances, there is a reason to keep around the byte str version of a
value. Here’s a few hints to keep your sanity in these situations:
1. Keep your unicode and str values separate. Just like the pain caused when you have to
use someone else’s library that returns both unicode and str you can cause yourself
pain if you have functions that can return both types or variables that could hold
either type of value.
2. Name your variables so that you can tell whether you’re storing byte str or unicode
string. One of the first things you end up having to do when debugging is determine
what type of string you have in a variable and what type of string you are expecting.
Naming your variables consistently so that you can tell which type they are supposed to
hold will save you from at least one of those steps.
3. When you get values initially, make sure that you’re dealing with the type of value
that you expect as you save it. You can use isinstance() or to_bytes() since
to_bytes() doesn’t do any modifications of the string if it’s already a str. When
using to_bytes() for this purpose you might want to use:
try:
b_input = to_bytes(input_should_be_bytes_already, errors='strict', nonstring='strict')
except:
handle_errors_somehow()
The reason is that the default of to_bytes() will take characters that are illegal in
the chosen encoding and transform them to replacement characters. Since the point of
keeping this data as a byte str is to keep the exact same bytes when you send it
outside of your code, changing things to replacement characters should be rasing red
flags that something is wrong. Setting errors to strict will raise an exception which
gives you an opportunity to fail gracefully.
4. Sometimes you will want to print out the values that you have in your byte str. When
you do this you will need to make sure that you transform unicode to str before
combining them. Also be sure that any other function calls (including gettext) are
going to give you strings that are the same type. For instance:
print to_bytes(_('Username: %(user)s'), 'utf-8') % {'user': b_username}
Gotchas and how to avoid them
Even when you have a good conceptual understanding of how python2 treats unicode and str
there are still some things that can surprise you. In most cases this is because, as
noted earlier, python or one of the python libraries you depend on is trying to convert a
value automatically and failing. Explicit conversion at the appropriate place usually
solves that.
str(obj)
One common idiom for getting a simple, string representation of an object is to use:
str(obj)
Unfortunately, this is not safe. Sometimes str(obj) will return unicode. Sometimes it
will return a byte str. Sometimes, it will attempt to convert from a unicode string to a
byte str, fail, and throw a UnicodeError. To be safe from all of these, first decide
whether you need unicode or str to be returned. Then use to_unicode() or to_bytes() to
get the simple representation like this:
u_representation = to_unicode(obj, nonstring='simplerepr')
b_representation = to_bytes(obj, nonstring='simplerepr')
print
python has a builtin print() statement that outputs strings to the terminal. This
originated in a time when python only dealt with byte str. When unicode strings came
about, some enhancements were made to the print() statement so that it could print those
as well. The enhancements make print() work most of the time. However, the times when it
doesn’t work tend to make for cryptic debugging.
The basic issue is that print() has to figure out what encoding to use when it prints a
unicode string to the terminal. When python is attached to your terminal (ie, you’re
running the interpreter or running a script that prints to the screen) python is able to
take the encoding value from your locale settings LC_ALL or LC_CTYPE and print the
characters allowed by that encoding. On most modern Unix systems, the encoding is utf-8
which means that you can print any unicode character without problem.
There are two common cases of things going wrong:
1. Someone has a locale set that does not accept all valid unicode characters. For
instance:
$ LC_ALL=C python
>>> print u'\ufffd'
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode character u'\ufffd' in position 0: ordinal not in range(128)
This often happens when a script that you’ve written and debugged from the terminal is
run from an automated environment like cron. It also occurs when you have written a
script using a utf-8 aware locale and released it for consumption by people all over
the internet. Inevitably, someone is running with a locale that can’t handle all
unicode characters and you get a traceback reported.
2. You redirect output to a file. Python isn’t using the values in LC_ALL unconditionally
to decide what encoding to use. Instead it is using the encoding set for the terminal
you are printing to which is set to accept different encodings by LC_ALL. If you
redirect to a file, you are no longer printing to the terminal so LC_ALL won’t have any
effect. At this point, python will decide it can’t find an encoding and fallback to
ASCII which will likely lead to UnicodeError being raised. You can see this in a short
script:
#! /usr/bin/python -tt
print u'\ufffd'
And then look at the difference between running it normally and redirecting to a file:
$ ./test.py
�
$ ./test.py > t
Traceback (most recent call last):
File "test.py", line 3, in <module>
print u'\ufffd'
UnicodeEncodeError: 'ascii' codec can't encode character u'\ufffd' in position 0: ordinal not in range(128)
The short answer to dealing with this is to always use bytes when writing output. You can
do this by explicitly converting to bytes like this:
from kitchen.text.converters import to_bytes
u_string = u'\ufffd'
print to_bytes(u_string)
or you can wrap stdout and stderr with a StreamWriter. A StreamWriter is convenient in
that you can assign it to encode for sys.stdout or sys.stderr and then have output
automatically converted but it has the drawback of still being able to throw UnicodeError
if the writer can’t encode all possible unicode codepoints. Kitchen provides an alternate
version which can be retrieved with kitchen.text.converters.getwriter() which will not
traceback in its standard configuration.
Unicode, str, and dict keys
The hash() of the ASCII characters is the same for unicode and byte str. When you use
them in dict keys, they evaluate to the same dictionary slot:
>>> u_string = u'a'
>>> b_string = 'a'
>>> hash(u_string), hash(b_string)
(12416037344, 12416037344)
>>> d = {}
>>> d[u_string] = 'unicode'
>>> d[b_string] = 'bytes'
>>> d
{u'a': 'bytes'}
When you deal with key values outside of ASCII, unicode and byte str evaluate unequally no
matter what their character content or hash value:
>>> u_string = u'ñ'
>>> b_string = u_string.encode('utf-8')
>>> print u_string
ñ
>>> print b_string
ñ
>>> d = {}
>>> d[u_string] = 'unicode'
>>> d[b_string] = 'bytes'
>>> d
{u'\\xf1': 'unicode', '\\xc3\\xb1': 'bytes'}
>>> b_string2 = '\\xf1'
>>> hash(u_string), hash(b_string2)
(30848092528, 30848092528)
>>> d = {}
>>> d[u_string] = 'unicode'
>>> d[b_string2] = 'bytes'
{u'\\xf1': 'unicode', '\\xf1': 'bytes'}
How do you work with this one? Remember rule #1: Keep your unicode and byte str values
separate. That goes for keys in a dictionary just like anything else.
• For any given dictionary, make sure that all your keys are either unicode or str. Do
not mix the two. If you’re being given both unicode and str but you don’t need to
preserve separate keys for each, I recommend using to_unicode() or to_bytes() to convert
all keys to one type or the other like this:
>>> from kitchen.text.converters import to_unicode
>>> u_string = u'one'
>>> b_string = 'two'
>>> d = {}
>>> d[to_unicode(u_string)] = 1
>>> d[to_unicode(b_string)] = 2
>>> d
{u'two': 2, u'one': 1}
• These issues also apply to using dicts with tuple keys that contain a mixture of unicode
and str. Once again the best fix is to standardise on either str or unicode.
• If you absolutely need to store values in a dictionary where the keys could be either
unicode or str you can use StrictDict which has separate entries for all unicode and
byte str and deals correctly with any tuple containing mixed unicode and byte str.
Functions
Unicode and byte str conversion
kitchen.text.converters.to_unicode(obj, encoding='utf-8', errors='replace',
nonstring=None, non_string=None)
Convert an object into a unicode string
Parameters
• obj – Object to convert to a unicode string. This should normally be a
byte str
• encoding – What encoding to try converting the byte str as. Defaults to
utf-8
• errors – If errors are found while decoding, perform this action.
Defaults to replace which replaces the invalid bytes with a character that
means the bytes were unable to be decoded. Other values are the same as
the error handling schemes in the codec base classes. For instance strict
which raises an exception and ignore which simply omits the non-decodable
characters.
• nonstring –
How to treat nonstring values. Possible values are:
simplerepr
Attempt to call the object’s “simple representation” method and
return that value. Python-2.3+ has two methods that try to return
a simple representation: object.__unicode__() and object.__str__().
We first try to get a usable value from object.__unicode__(). If
that fails we try the same with object.__str__().
empty Return an empty unicode string
strict Raise a TypeError
passthru
Return the object unchanged
repr Attempt to return a unicode string of the repr of the object
Default is simplerepr
• non_string – Deprecated Use nonstring instead
Raises
• TypeError – if nonstring is strict and a non-basestring object is passed
in or if nonstring is set to an unknown value
• UnicodeDecodeError – if errors is strict and obj is not decodable using
the given encoding
Returns
unicode string or the original object depending on the value of nonstring.
Usually this should be used on a byte str but it can take both byte str and unicode
strings intelligently. Nonstring objects are handled in different ways depending
on the setting of the nonstring parameter.
The default values of this function are set so as to always return a unicode string
and never raise an error when converting from a byte str to a unicode string.
However, when you do not pass validly encoded text (or a nonstring object), you may
end up with output that you don’t expect. Be sure you understand the requirements
of your data, not just ignore errors by passing it through this function.
Changed in version 0.2.1a2: Deprecated non_string in favor of nonstring parameter
and changed default value to simplerepr
kitchen.text.converters.to_bytes(obj, encoding='utf-8', errors='replace', nonstring=None,
non_string=None)
Convert an object into a byte str
Parameters
• obj – Object to convert to a byte str. This should normally be a unicode
string.
• encoding – Encoding to use to convert the unicode string into a byte str.
Defaults to utf-8.
• errors –
If errors are found while encoding, perform this action. Defaults to
replace which replaces the invalid bytes with a character that means the
bytes were unable to be encoded. Other values are the same as the error
handling schemes in the codec base classes. For instance strict which
raises an exception and ignore which simply omits the non-encodable
characters.
• nonstring –
How to treat nonstring values. Possible values are:
simplerepr
Attempt to call the object’s “simple representation” method and
return that value. Python-2.3+ has two methods that try to return
a simple representation: object.__unicode__() and object.__str__().
We first try to get a usable value from object.__str__(). If that
fails we try the same with object.__unicode__().
empty Return an empty byte str
strict Raise a TypeError
passthru
Return the object unchanged
repr Attempt to return a byte str of the repr() of the object
Default is simplerepr.
• non_string – Deprecated Use nonstring instead.
Raises
• TypeError – if nonstring is strict and a non-basestring object is passed
in or if nonstring is set to an unknown value.
• UnicodeEncodeError – if errors is strict and all of the bytes of obj are
unable to be encoded using encoding.
Returns
byte str or the original object depending on the value of nonstring.
WARNING:
If you pass a byte str into this function the byte str is returned unmodified.
It is not re-encoded with the specified encoding. The easiest way to achieve
that is:
to_bytes(to_unicode(text), encoding='utf-8')
The initial to_unicode() call will ensure text is a unicode string. Then,
to_bytes() will turn that into a byte str with the specified encoding.
Usually, this should be used on a unicode string but it can take either a byte str
or a unicode string intelligently. Nonstring objects are handled in different ways
depending on the setting of the nonstring parameter.
The default values of this function are set so as to always return a byte str and
never raise an error when converting from unicode to bytes. However, when you do
not pass an encoding that can validly encode the object (or a non-string object),
you may end up with output that you don’t expect. Be sure you understand the
requirements of your data, not just ignore errors by passing it through this
function.
Changed in version 0.2.1a2: Deprecated non_string in favor of nonstring parameter
and changed default value to simplerepr
kitchen.text.converters.getwriter(encoding)
Return a codecs.StreamWriter that resists tracing back.
Parameters
encoding – Encoding to use for transforming unicode strings into byte str.
Return type
codecs.StreamWriter
Returns
StreamWriter that you can instantiate to wrap output streams to
automatically translate unicode strings into encoding.
This is a reimplemetation of codecs.getwriter() that returns a StreamWriter that
resists issuing tracebacks. The StreamWriter that is returned uses
kitchen.text.converters.to_bytes() to convert unicode strings into byte str. The
departures from codecs.getwriter() are:
1. The StreamWriter that is returned will take byte str as well as unicode strings.
Any byte str will be passed through unmodified.
2. The default error handler for unknown bytes is to replace the bytes with the
unknown character (? in most ascii-based encodings, � in the utf encodings)
whereas codecs.getwriter() defaults to strict. Like codecs.StreamWriter, the
returned StreamWriter can have its error handler changed in code by setting
stream.errors = 'new_handler_name'
Example usage:
$ LC_ALL=C python
>>> import sys
>>> from kitchen.text.converters import getwriter
>>> UTF8Writer = getwriter('utf-8')
>>> unwrapped_stdout = sys.stdout
>>> sys.stdout = UTF8Writer(unwrapped_stdout)
>>> print 'caf\xc3\xa9'
café
>>> print u'caf\xe9'
café
>>> ASCIIWriter = getwriter('ascii')
>>> sys.stdout = ASCIIWriter(unwrapped_stdout)
>>> print 'caf\xc3\xa9'
café
>>> print u'caf\xe9'
caf?
SEE ALSO:
API docs for codecs.StreamWriter and codecs.getwriter() and Print Fails on the
python wiki.
New in version kitchen: 0.2a2, API: kitchen.text 1.1.0
kitchen.text.converters.to_str(obj)
Deprecated
This function converts something to a byte str if it isn’t one. It’s used to call
str() or unicode() on the object to get its simple representation without danger of
getting a UnicodeError. You should be using to_unicode() or to_bytes() explicitly
instead.
If you need unicode strings:
to_unicode(obj, nonstring='simplerepr')
If you need byte str:
to_bytes(obj, nonstring='simplerepr')
kitchen.text.converters.to_utf8(obj, errors='replace', non_string='passthru')
Deprecated
Convert unicode to an encoded utf-8 byte str. You should be using to_bytes()
instead:
to_bytes(obj, encoding='utf-8', non_string='passthru')
Transformation to XML
kitchen.text.converters.unicode_to_xml(string, encoding='utf-8', attrib=False,
control_chars='replace')
Take a unicode string and turn it into a byte str suitable for xml
Parameters
• string – unicode string to encode into an XML compatible byte str
• encoding – encoding to use for the returned byte str. Default is to
encode to UTF-8. If some of the characters in string are not encodable in
this encoding, the unknown characters will be entered into the output
string using xml character references.
• attrib – If True, quote the string for use in an xml attribute. If False
(default), quote for use in an xml text field.
• control_chars –
control characters are not allowed in XML documents. When we encounter
those we need to know what to do. Valid options are:
replace
(default) Replace the control characters with ?
ignore Remove the characters altogether from the output
strict Raise an XmlEncodeError when we encounter a control character
Raises
• kitchen.text.exceptions.XmlEncodeError – If control_chars is set to strict
and the string to be made suitable for output to xml contains control
characters or if string is not a unicode string then we raise this
exception.
• ValueError – If control_chars is set to something other than replace,
ignore, or strict.
Return type
byte str
Returns
representation of the unicode string as a valid XML byte str
XML files consist mainly of text encoded using a particular charset. XML also
denies the use of certain bytes in the encoded text (example: ASCII Null). There
are also special characters that must be escaped if they are present in the input
(example: <). This function takes care of all of those issues for you.
There are a few different ways to use this function depending on your needs. The
simplest invocation is like this:
unicode_to_xml(u'String with non-ASCII characters: <"á と">')
This will return the following to you, encoded in utf-8:
'String with non-ASCII characters: <"á と">'
Pretty straightforward. Now, what if you need to encode your document in something
other than utf-8? For instance, latin-1? Let’s see:
unicode_to_xml(u'String with non-ASCII characters: <"á と">', encoding='latin-1')
'String with non-ASCII characters: <"á と">'
Because the と character is not available in the latin-1 charset, it is replaced
with と in our output. This is an xml character reference which represents
the character at unicode codepoint 12392, the と character.
When you want to reverse this, use xml_to_unicode() which will turn a byte str into
a unicode string and replace the xml character references with the unicode
characters.
XML also has the quirk of not allowing control characters in its output. The
control_chars parameter allows us to specify what to do with those. For use cases
that don’t need absolute character by character fidelity (example: holding strings
that will just be used for display in a GUI app later), the default value of
replace works well:
unicode_to_xml(u'String with disallowed control chars: \u0000\u0007')
'String with disallowed control chars: ??'
If you do need to be able to reproduce all of the characters at a later date
(examples: if the string is a key value in a database or a path on a filesystem)
you have many choices. Here are a few that rely on utf-7, a verbose encoding that
encodes control characters (as well as non-ASCII unicode values) to characters from
within the ASCII printable characters. The good thing about doing this is that the
code is pretty simple. You just need to use utf-7 both when encoding the field for
xml and when decoding it for use in your python program:
unicode_to_xml(u'String with unicode: と and control char: \u0007', encoding='utf7')
'String with unicode: +MGg and control char: +AAc-'
# [...]
xml_to_unicode('String with unicode: +MGg and control char: +AAc-', encoding='utf7')
u'String with unicode: と and control char: \u0007'
As you can see, the utf-7 encoding will transform even characters that would be
representable in utf-8. This can be a drawback if you want unicode characters in
the file to be readable without being decoded first. You can work around this with
increased complexity in your application code:
encoding = 'utf-8'
u_string = u'String with unicode: と and control char: \u0007'
try:
# First attempt to encode to utf8
data = unicode_to_xml(u_string, encoding=encoding, errors='strict')
except XmlEncodeError:
# Fallback to utf-7
encoding = 'utf-7'
data = unicode_to_xml(u_string, encoding=encoding, errors='strict')
write_tag('<mytag encoding=%s>%s</mytag>' % (encoding, data))
# [...]
encoding = tag.attributes.encoding
u_string = xml_to_unicode(u_string, encoding=encoding)
Using code similar to that, you can have some fields encoded using your default
encoding and fallback to utf-7 if there are control characters present.
NOTE:
If your goal is to preserve the control characters you cannot save the entire
file as utf-7 and set the xml encoding parameter to utf-7 if your goal is to
preserve the control characters. Because XML doesn’t allow control characters,
you have to encode those separate from any encoding work that the XML parser
itself knows about.
SEE ALSO:
bytes_to_xml()
if you’re dealing with bytes that are non-text or of an unknown encoding
that you must preserve on a byte for byte level.
guess_encoding_to_xml()
if you’re dealing with strings in unknown encodings that you don’t need
to save with char-for-char fidelity.
kitchen.text.converters.xml_to_unicode(byte_string, encoding='utf-8', errors='replace')
Transform a byte str from an xml file into a unicode string
Parameters
• byte_string – byte str to decode
• encoding – encoding that the byte str is in
• errors – What to do if not every character is valid in encoding. See the
to_unicode() documentation for legal values.
Return type
unicode string
Returns
string decoded from byte_string
This function attempts to reverse what unicode_to_xml() does. It takes a byte str
(presumably read in from an xml file) and expands all the html entities into
unicode characters and decodes the byte str into a unicode string. One thing it
cannot do is restore any control characters that were removed prior to inserting
into the file. If you need to keep such characters you need to use xml_to_bytes()
and bytes_to_xml() or use on of the strategies documented in unicode_to_xml()
instead.
kitchen.text.converters.byte_string_to_xml(byte_string, input_encoding='utf-8',
errors='replace', output_encoding='utf-8', attrib=False, control_chars='replace')
Make sure a byte str is validly encoded for xml output
Parameters
• byte_string – Byte str to turn into valid xml output
• input_encoding – Encoding of byte_string. Default utf-8
• errors –
How to handle errors encountered while decoding the byte_string into
unicode at the beginning of the process. Values are:
replace
(default) Replace the invalid bytes with a ?
ignore Remove the characters altogether from the output
strict Raise an UnicodeDecodeError when we encounter a non-decodable
character
• output_encoding – Encoding for the xml file that this string will go into.
Default is utf-8. If all the characters in byte_string are not encodable
in this encoding, the unknown characters will be entered into the output
string using xml character references.
• attrib – If True, quote the string for use in an xml attribute. If False
(default), quote for use in an xml text field.
• control_chars –
XML does not allow control characters. When we encounter those we need to
know what to do. Valid options are:
replace
(default) Replace the control characters with ?
ignore Remove the characters altogether from the output
strict Raise an error when we encounter a control character
Raises
• XmlEncodeError – If control_chars is set to strict and the string to be
made suitable for output to xml contains control characters then we raise
this exception.
• UnicodeDecodeError – If errors is set to strict and the byte_string
contains bytes that are not decodable using input_encoding, this error is
raised
Return type
byte str
Returns
representation of the byte str in the output encoding with any bytes that
aren’t available in xml taken care of.
Use this when you have a byte str representing text that you need to make suitable
for output to xml. There are several cases where this is the case. For instance,
if you need to transform some strings encoded in latin-1 to utf-8 for output:
utf8_string = byte_string_to_xml(latin1_string, input_encoding='latin-1')
If you already have strings in the proper encoding you may still want to use this
function to remove control characters:
cleaned_string = byte_string_to_xml(string, input_encoding='utf-8', output_encoding='utf-8')
SEE ALSO:
unicode_to_xml()
for other ideas on using this function
kitchen.text.converters.xml_to_byte_string(byte_string, input_encoding='utf-8',
errors='replace', output_encoding='utf-8')
Transform a byte str from an xml file into unicode string
Parameters
• byte_string – byte str to decode
• input_encoding – encoding that the byte str is in
• errors – What to do if not every character is valid in encoding. See the
to_unicode() docstring for legal values.
• output_encoding – Encoding for the output byte str
Returns
unicode string decoded from byte_string
This function attempts to reverse what unicode_to_xml() does. It takes a byte str
(presumably read in from an xml file) and expands all the html entities into
unicode characters and decodes the byte str into a unicode string. One thing it
cannot do is restore any control characters that were removed prior to inserting
into the file. If you need to keep such characters you need to use xml_to_bytes()
and bytes_to_xml() or use one of the strategies documented in unicode_to_xml()
instead.
kitchen.text.converters.bytes_to_xml(byte_string, *args, **kwargs)
Return a byte str encoded so it is valid inside of any xml file
Parameters
• byte_string – byte str to transform
• **kwargs (*args,) – extra arguments to this function are passed on to the
function actually implementing the encoding. You can use this to tweak
the output in some cases but, as a general rule, you shouldn’t because the
underlying encoding function is not guaranteed to remain the same.
Return type
byte str consisting of all ASCII characters
Returns
byte str representation of the input. This will be encoded using base64.
This function is made especially to put binary information into xml documents.
This function is intended for encoding things that must be preserved byte-for-byte.
If you want to encode a byte string that’s text and don’t mind losing the actual
bytes you probably want to try byte_string_to_xml() or guess_encoding_to_xml()
instead.
NOTE:
Although the current implementation uses base64.b64encode() and there’s no plans
to change it, that isn’t guaranteed. If you want to make sure that you can
encode and decode these messages it’s best to use xml_to_bytes() if you use this
function to encode.
kitchen.text.converters.xml_to_bytes(byte_string, *args, **kwargs)
Decode a string encoded using bytes_to_xml()
Parameters
• byte_string – byte str to transform. This should be a base64 encoded
sequence of bytes originally generated by bytes_to_xml().
• **kwargs (*args,) – extra arguments to this function are passed on to the
function actually implementing the encoding. You can use this to tweak
the output in some cases but, as a general rule, you shouldn’t because the
underlying encoding function is not guaranteed to remain the same.
Return type
byte str
Returns
byte str that’s the decoded input
If you’ve got fields in an xml document that were encoded with bytes_to_xml() then
you want to use this function to undecode them. It converts a base64 encoded
string into a byte str.
NOTE:
Although the current implementation uses base64.b64decode() and there’s no plans
to change it, that isn’t guaranteed. If you want to make sure that you can
encode and decode these messages it’s best to use bytes_to_xml() if you use this
function to decode.
kitchen.text.converters.guess_encoding_to_xml(string, output_encoding='utf-8',
attrib=False, control_chars='replace')
Return a byte str suitable for inclusion in xml
Parameters
• string – unicode or byte str to be transformed into a byte str suitable
for inclusion in xml. If string is a byte str we attempt to guess the
encoding. If we cannot guess, we fallback to latin-1.
• output_encoding – Output encoding for the byte str. This should match the
encoding of your xml file.
• attrib – If True, escape the item for use in an xml attribute. If False
(default) escape the item for use in a text node.
Returns
utf-8 encoded byte str
kitchen.text.converters.to_xml(string, encoding='utf-8', attrib=False,
control_chars='ignore')
Deprecated: Use guess_encoding_to_xml() instead
Working with exception messages
kitchen.text.converters.EXCEPTION_CONVERTERS = (<function <lambda>>, <function <lambda>>)
Tuple of functions to try to use to convert an exception into a string
representation. Its main use is to extract a string (unicode or str) from
an exception object in exception_to_unicode() and exception_to_bytes(). The
functions here will try the exception’s args[0] and the exception itself
(roughly equivalent to str(exception)) to extract the message. This is only
a default and can be easily overridden when calling those functions. There
are several reasons you might wish to do that. If you have exceptions where
the best string representing the exception is not returned by the default
functions, you can add another function to extract from a different field:
from kitchen.text.converters import (EXCEPTION_CONVERTERS,
exception_to_unicode)
class MyError(Exception):
def __init__(self, message):
self.value = message
c = [lambda e: e.value]
c.extend(EXCEPTION_CONVERTERS)
try:
raise MyError('An Exception message')
except MyError, e:
print exception_to_unicode(e, converters=c)
Another reason would be if you’re converting to a byte str and you know the
str needs to be a non-utf-8 encoding. exception_to_bytes() defaults to
utf-8 but if you convert into a byte str explicitly using a converter then
you can choose a different encoding:
from kitchen.text.converters import (EXCEPTION_CONVERTERS,
exception_to_bytes, to_bytes)
c = [lambda e: to_bytes(e.args[0], encoding='euc_jp'),
lambda e: to_bytes(e, encoding='euc_jp')]
c.extend(EXCEPTION_CONVERTERS)
try:
do_something()
except Exception, e:
log = open('logfile.euc_jp', 'a')
log.write('%s
‘ % exception_to_bytes(e, converters=c)
log.close()
Each function in this list should take the exception as its sole argument
and return a string containing the message representing the exception. The
functions may return the message as a :byte class:str, a unicode string, or
even an object if you trust the object to return a decent string
representation. The exception_to_unicode() and exception_to_bytes()
functions will make sure to convert the string to the proper type before
returning.
New in version 0.2.2.
kitchen.text.converters.BYTE_EXCEPTION_CONVERTERS = (<function <lambda>>, <function
to_bytes>)
Deprecated: Use EXCEPTION_CONVERTERS instead.
Tuple of functions to try to use to convert an exception into a string
representation. This tuple is similar to the one in EXCEPTION_CONVERTERS but it’s
used with exception_to_bytes() instead. Ideally, these functions should do their
best to return the data as a byte str but the results will be run through
to_bytes() before being returned.
New in version 0.2.2.
Changed in version 1.0.1: Deprecated as simplifications allow EXCEPTION_CONVERTERS
to perform the same function.
kitchen.text.converters.exception_to_unicode(exc, converters=(<function <lambda>>,
<function <lambda>>))
Convert an exception object into a unicode representation
Parameters
• exc – Exception object to convert
• converters – List of functions to use to convert the exception into a
string. See EXCEPTION_CONVERTERS for the default value and an example of
adding other converters to the defaults. The functions in the list are
tried one at a time to see if they can extract a string from the
exception. The first one to do so without raising an exception is used.
Returns
unicode string representation of the exception. The value extracted by the
converters will be converted into unicode before being returned using the
utf-8 encoding. If you know you need to use an alternate encoding add a
function that does that to the list of functions in converters)
New in version 0.2.2.
kitchen.text.converters.exception_to_bytes(exc, converters=(<function <lambda>>, <function
<lambda>>))
Convert an exception object into a str representation
Parameters
• exc – Exception object to convert
• converters – List of functions to use to convert the exception into a
string. See EXCEPTION_CONVERTERS for the default value and an example of
adding other converters to the defaults. The functions in the list are
tried one at a time to see if they can extract a string from the
exception. The first one to do so without raising an exception is used.
Returns
byte str representation of the exception. The value extracted by the
converters will be converted into str before being returned using the utf-8
encoding. If you know you need to use an alternate encoding add a function
that does that to the list of functions in converters)
New in version 0.2.2.
Changed in version 1.0.1: Code simplification allowed us to switch to using
EXCEPTION_CONVERTERS as the default value of converters.
Format Text for Display
Functions related to displaying unicode text. Unicode characters don’t all have the same
width so we need helper functions for displaying them.
New in version 0.2: kitchen.display API 1.0.0
kitchen.text.display.textual_width(msg, control_chars='guess', encoding='utf-8',
errors='replace')
Get the textual width of a string
Parameters
• msg – unicode string or byte str to get the width of
• control_chars –
specify how to deal with control characters. Possible values are:
guess (default) will take a guess for control character widths. Most
codes will return zero width. backspace, delete, and clear delete
return -1. escape currently returns -1 as well but this is not
guaranteed as it’s not always correct
strict will raise kitchen.text.exceptions.ControlCharError if a control
character is encountered
• encoding – If we are given a byte str this is used to decode it into
unicode string. Any characters that are not decodable in this encoding
will get a value dependent on the errors parameter.
• errors – How to treat errors encoding the byte str to unicode string.
Legal values are the same as for kitchen.text.converters.to_unicode().
The default value of replace will cause undecodable byte sequences to have
a width of one. ignore will have a width of zero.
Raises ControlCharError – if msg contains a control character and control_chars is
strict.
Returns
Textual width of the msg. This is the amount of space that the string will
consume on a monospace display. It’s measured in the number of cell
positions or columns it will take up on a monospace display. This is not
the number of glyphs that are in the string.
NOTE:
This function can be wrong sometimes because Unicode does not specify a strict
width value for all of the code points. In particular, we’ve found that some
Tamil characters take up to four character cells but we return a lesser amount.
kitchen.text.display.textual_width_chop(msg, chop, encoding='utf-8', errors='replace')
Given a string, return it chopped to a given textual width
Parameters
• msg – unicode string or byte str to chop
• chop – Chop msg if it exceeds this textual width
• encoding – If we are given a byte str, this is used to decode it into a
unicode string. Any characters that are not decodable in this encoding
will be assigned a width of one.
• errors – How to treat errors encoding the byte str to unicode. Legal
values are the same as for kitchen.text.converters.to_unicode()
Return type
unicode string
Returns
unicode string of the msg chopped at the given textual width
This is what you want to use instead of %.*s, as it does the “right” thing with
regard to UTF-8 sequences, control characters, and characters that take more than
one cell position. Eg:
>>> # Wrong: only displays 8 characters because it is operating on bytes
>>> print "%.*s" % (10, 'café ñunru!')
café ñun
>>> # Properly operates on graphemes
>>> '%s' % (textual_width_chop('café ñunru!', 10))
café ñunru
>>> # takes too many columns because the kanji need two cell positions
>>> print '1234567890\n%.*s' % (10, u'一二三四五六七八九十')
1234567890
一二三四五六七八九十
>>> # Properly chops at 10 columns
>>> print '1234567890\n%s' % (textual_width_chop(u'一二三四五六七八九十', 10))
1234567890
一二三四五
kitchen.text.display.textual_width_fill(msg, fill, chop=None, left=True, prefix='',
suffix='')
Expand a unicode string to a specified textual width or chop to same
Parameters
• msg – unicode string to format
• fill – pad string until the textual width of the string is this length
• chop – before doing anything else, chop the string to this length.
Default: Don’t chop the string at all
• left – If True (default) left justify the string and put the padding on
the right. If False, pad on the left side.
• prefix – Attach this string before the field we’re filling
• suffix – Append this string to the end of the field we’re filling
Return type
unicode string
Returns
msg formatted to fill the specified width. If no chop is specified, the
string could exceed the fill length when completed. If prefix or suffix are
printable characters, the string could be longer than the fill width.
NOTE:
prefix and suffix should be used for “invisible” characters like highlighting,
color changing escape codes, etc. The fill characters are appended outside of
any prefix or suffix elements. This allows you to only highlight msg inside of
the field you’re filling.
WARNING:
msg, prefix, and suffix should all be representable as unicode characters. In
particular, any escape sequences in prefix and suffix need to be convertible to
unicode. If you need to use byte sequences here rather than unicode characters,
use byte_string_textual_width_fill() instead.
This function expands a string to fill a field of a particular textual width. Use
it instead of %*.*s, as it does the “right” thing with regard to UTF-8 sequences,
control characters, and characters that take more than one cell position in a
display. Example usage:
>>> msg = u'一二三四五六七八九十'
>>> # Wrong: This uses 10 characters instead of 10 cells:
>>> u":%-*.*s:" % (10, 10, msg[:9])
:一二三四五六七八九 :
>>> # This uses 10 cells like we really want:
>>> u":%s:" % (textual_width_fill(msg[:9], 10, 10))
:一二三四五:
>>> # Wrong: Right aligned in the field, but too many cells
>>> u"%20.10s" % (msg)
一二三四五六七八九十
>>> # Correct: Right aligned with proper number of cells
>>> u"%s" % (textual_width_fill(msg, 20, 10, left=False))
一二三四五
>>> # Wrong: Adding some escape characters to highlight the line but too many cells
>>> u"%s%20.10s%s" % (prefix, msg, suffix)
u'[7m 一二三四五六七八九十[0m'
>>> # Correct highlight of the line
>>> u"%s%s%s" % (prefix, display.textual_width_fill(msg, 20, 10, left=False), suffix)
u'[7m 一二三四五[0m'
>>> # Correct way to not highlight the fill
>>> u"%s" % (display.textual_width_fill(msg, 20, 10, left=False, prefix=prefix, suffix=suffix))
u' [7m一二三四五[0m'
kitchen.text.display.wrap(text, width=70, initial_indent=u'', subsequent_indent=u'',
encoding='utf-8', errors='replace')
Works like we want textwrap.wrap() to work,
Parameters
• text – unicode string or byte str to wrap
• width – textual width at which to wrap. Default: 70
• initial_indent – string to use to indent the first line. Default: do not
indent.
• subsequent_indent – string to use to wrap subsequent lines. Default: do
not indent
• encoding – Encoding to use if text is a byte str
• errors – error handler to use if text is a byte str and contains some
undecodable characters.
Return type
list of unicode strings
Returns
list of lines that have been text wrapped and indented.
textwrap.wrap() from the python standard library has two drawbacks that this
attempts to fix:
1. It does not handle textual width. It only operates on bytes or characters which
are both inadequate (due to multi-byte and double width characters).
2. It malforms lists and blocks.
kitchen.text.display.fill(text, *args, **kwargs)
Works like we want textwrap.fill() to work
Parameters
text – unicode string or byte str to process
Returns
unicode string with each line separated by a newline
SEE ALSO:
kitchen.text.display.wrap()
for other parameters that you can give this command.
This function is a light wrapper around kitchen.text.display.wrap(). Where that
function returns a list of lines, this function returns one string with each line
separated by a newline.
kitchen.text.display.byte_string_textual_width_fill(msg, fill, chop=None, left=True,
prefix='', suffix='', encoding='utf-8', errors='replace')
Expand a byte str to a specified textual width or chop to same
Parameters
• msg – byte str encoded in UTF-8 that we want formatted
• fill – pad msg until the textual width is this long
• chop – before doing anything else, chop the string to this length.
Default: Don’t chop the string at all
• left – If True (default) left justify the string and put the padding on
the right. If False, pad on the left side.
• prefix – Attach this byte str before the field we’re filling
• suffix – Append this byte str to the end of the field we’re filling
Return type
byte str
Returns
msg formatted to fill the specified textual width. If no chop is specified,
the string could exceed the fill length when completed. If prefix or suffix
are printable characters, the string could be longer than fill width.
NOTE:
prefix and suffix should be used for “invisible” characters like highlighting,
color changing escape codes, etc. The fill characters are appended outside of
any prefix or suffix elements. This allows you to only highlight msg inside of
the field you’re filling.
SEE ALSO:
textual_width_fill()
For example usage. This function has only two differences.
1. it takes byte str for prefix and suffix so you can pass in arbitrary
sequences of bytes, not just unicode characters.
2. it returns a byte str instead of a unicode string.
Internal Data
There are a few internal functions and variables in this module. Code outside of kitchen
shouldn’t use them but people coding on kitchen itself may find them useful.
kitchen.text.display._COMBINING = ((768, 879), (1155, 1161), (1425, 1469), (1471, 1471),
(1473, 1474), (1476, 1477), (1479, 1479), (1536, 1539), (1552, 1562), (1611, 1631), (1648,
1648), (1750, 1764), (1767, 1768), (1770, 1773), (1807, 1807), (1809, 1809), (1840, 1866),
(1958, 1968), (2027, 2035), (2070, 2073), (2075, 2083), (2085, 2087), (2089, 2093), (2137,
2139), (2260, 2273), (2275, 2303), (2305, 2306), (2364, 2364), (2369, 2376), (2381, 2381),
(2385, 2388), (2402, 2403), (2433, 2433), (2492, 2492), (2497, 2500), (2509, 2509), (2530,
2531), (2561, 2562), (2620, 2620), (2625, 2626), (2631, 2632), (2635, 2637), (2672, 2673),
(2689, 2690), (2748, 2748), (2753, 2757), (2759, 2760), (2765, 2765), (2786, 2787), (2817,
2817), (2876, 2876), (2879, 2879), (2881, 2883), (2893, 2893), (2902, 2902), (2946, 2946),
(3008, 3008), (3021, 3021), (3134, 3136), (3142, 3144), (3146, 3149), (3157, 3158), (3260,
3260), (3263, 3263), (3270, 3270), (3276, 3277), (3298, 3299), (3393, 3395), (3405, 3405),
(3530, 3530), (3538, 3540), (3542, 3542), (3633, 3633), (3636, 3642), (3655, 3662), (3761,
3761), (3764, 3769), (3771, 3772), (3784, 3789), (3864, 3865), (3893, 3893), (3895, 3895),
(3897, 3897), (3953, 3966), (3968, 3972), (3974, 3975), (3984, 3991), (3993, 4028), (4038,
4038), (4141, 4144), (4146, 4146), (4150, 4151), (4153, 4154), (4184, 4185), (4237, 4237),
(4448, 4607), (4957, 4959), (5906, 5908), (5938, 5940), (5970, 5971), (6002, 6003), (6068,
6069), (6071, 6077), (6086, 6086), (6089, 6099), (6109, 6109), (6155, 6157), (6313, 6313),
(6432, 6434), (6439, 6440), (6450, 6450), (6457, 6459), (6679, 6680), (6752, 6752), (6773,
6780), (6783, 6783), (6832, 6845), (6912, 6915), (6964, 6964), (6966, 6970), (6972, 6972),
(6978, 6978), (6980, 6980), (7019, 7027), (7082, 7083), (7142, 7142), (7154, 7155), (7223,
7223), (7376, 7378), (7380, 7392), (7394, 7400), (7405, 7405), (7412, 7412), (7416, 7417),
(7616, 7669), (7675, 7679), (8203, 8207), (8234, 8238), (8288, 8291), (8298, 8303), (8400,
8432), (11503, 11505), (11647, 11647), (11744, 11775), (12330, 12335), (12441, 12442),
(42607, 42607), (42612, 42621), (42654, 42655), (42736, 42737), (43014, 43014), (43019,
43019), (43045, 43046), (43204, 43204), (43232, 43249), (43307, 43309), (43347, 43347),
(43443, 43443), (43456, 43456), (43696, 43696), (43698, 43700), (43703, 43704), (43710,
43711), (43713, 43713), (43766, 43766), (44013, 44013), (64286, 64286), (65024, 65039),
(65056, 65071), (65279, 65279), (65529, 65531), (66045, 66045), (66272, 66272), (66422,
66426), (68097, 68099), (68101, 68102), (68108, 68111), (68152, 68154), (68159, 68159),
(68325, 68326), (69702, 69702), (69759, 69759), (69817, 69818), (69888, 69890), (69939,
69940), (70003, 70003), (70080, 70080), (70090, 70090), (70197, 70198), (70377, 70378),
(70460, 70460), (70477, 70477), (70502, 70508), (70512, 70516), (70722, 70722), (70726,
70726), (70850, 70851), (71103, 71104), (71231, 71231), (71350, 71351), (71467, 71467),
(72767, 72767), (92912, 92916), (92976, 92982), (113822, 113822), (119141, 119145),
(119149, 119170), (119173, 119179), (119210, 119213), (119362, 119364), (122880, 122886),
(122888, 122904), (122907, 122913), (122915, 122916), (122918, 122922), (125136, 125142),
(125252, 125258), (917505, 917505), (917536, 917631), (917760, 917999))
Internal table, provided by this module to list code points which combine with
other characters and therefore should have no textual width. This is a sorted
tuple of non-overlapping intervals. Each interval is a tuple listing a starting
code point and ending code point. Every code point between the two end points is a
combining character.
SEE ALSO:
_generate_combining_table()
for how this table is generated
This table was last regenerated on python-3.6.0-rc1 with
unicodedata.unidata_version 9.0.0
kitchen.text.display._generate_combining_table()
Combine Markus Kuhn’s data with unicodedata to make combining char list
Return type
tuple of tuples
Returns
tuple of intervals of code points that are combining character. Each
interval is a 2-tuple of the starting code point and the ending code point
for the combining characters.
In normal use, this function serves to tell how we’re generating the combining char
list. For speed reasons, we use this to generate a static list and just use that
later.
Markus Kuhn’s list of combining characters is more complete than what’s in the
python unicodedata library but the python unicodedata is synced against later
versions of the unicode database
This is used to generate the _COMBINING table.
kitchen.text.display._print_combining_table()
Print out a new _COMBINING table
This will print a new _COMBINING table in the format used in
kitchen/text/display.py. It’s useful for updating the _COMBINING table with
updated data from a new python as the format won’t change from what’s already in
the file.
kitchen.text.display._interval_bisearch(value, table)
Binary search in an interval table.
Parameters
• value – numeric value to search for
• table – Ordered list of intervals. This is a list of two-tuples. The
elements of the two-tuple define an interval’s start and end points.
Returns
If value is found within an interval in the table return True. Otherwise,
False
This function checks whether a numeric value is present within a table of
intervals. It checks using a binary search algorithm, dividing the list of values
in half and checking against the values until it determines whether the value is in
the table.
kitchen.text.display._ucp_width(ucs, control_chars='guess')
Get the textual width of a ucs character
Parameters
• ucs – integer representing a single unicode code point
• control_chars –
specify how to deal with control characters. Possible values are:
guess (default) will take a guess for control character widths. Most
codes will return zero width. backspace, delete, and clear delete
return -1. escape currently returns -1 as well but this is not
guaranteed as it’s not always correct
strict will raise ControlCharError if a control character is encountered
Raises ControlCharError – if the code point is a unicode control character and
control_chars is set to ‘strict’
Returns
textual width of the character.
NOTE:
It’s important to remember this is textual width and not the number of
characters or bytes.
kitchen.text.display._textual_width_le(width, *args)
Optimize the common case when deciding which textual width is larger
Parameters
• width – textual width to compare against.
• *args – unicode strings to check the total textual width of
Returns
True if the total length of args are less than or equal to width. Otherwise
False.
We often want to know “does X fit in Y”. It takes a while to use textual_width()
to calculate this. However, we know that the number of canonically composed
unicode characters is always going to have 1 or 2 for the textual width per
character. With this we can take the following shortcuts:
1. If the number of canonically composed characters is more than width, the true
textual width cannot be less than width.
2. If the number of canonically composed characters * 2 is less than the width then
the textual width must be ok.
textual width of a canonically composed unicode string will always be greater than
or equal to the the number of unicode characters. So we can first check if the
number of composed unicode characters is less than the asked for width. If it is
we can return True immediately. If not, then we must do a full textual width
lookup.
Miscellaneous functions for manipulating text
Collection of text functions that don’t fit in another category.
Changed in version kitchen: 1.2.0, API: kitchen.text 2.2.0 Added isbasestring(),
isbytestring(), and isunicodestring() to help tell which string type is which on python2
and python3
kitchen.text.misc.byte_string_valid_encoding(byte_string, encoding='utf-8')
Detect if a byte str is valid in a specific encoding
Parameters
• byte_string – Byte str to test for bytes not valid in this encoding
• encoding – encoding to test against. Defaults to UTF-8.
Returns
True if there are no invalid UTF-8 characters. False if an invalid
character is detected.
NOTE:
This function checks whether the byte str is valid in the specified encoding.
It does not detect whether the byte str actually was encoded in that encoding.
If you want that sort of functionality, you probably want to use
guess_encoding() instead.
kitchen.text.misc.byte_string_valid_xml(byte_string, encoding='utf-8')
Check that a byte str would be valid in xml
Parameters
• byte_string – Byte str to check
• encoding – Encoding of the xml file. Default: UTF-8
Returns
True if the string is valid. False if it would be invalid in the xml file
In some cases you’ll have a whole bunch of byte strings and rather than
transforming them to unicode and back to byte str for output to xml, you will just
want to make sure they work with the xml file you’re constructing. This function
will help you do that. Example:
ARRAY_OF_MOSTLY_UTF8_STRINGS = [...]
processed_array = []
for string in ARRAY_OF_MOSTLY_UTF8_STRINGS:
if byte_string_valid_xml(string, 'utf-8'):
processed_array.append(string)
else:
processed_array.append(guess_bytes_to_xml(string, encoding='utf-8'))
output_xml(processed_array)
kitchen.text.misc.guess_encoding(byte_string, disable_chardet=False)
Try to guess the encoding of a byte str
Parameters
• byte_string – byte str to guess the encoding of
• disable_chardet – If this is True, we never attempt to use chardet to
guess the encoding. This is useful if you need to have reproducibility
whether chardet is installed or not. Default: False.
Raises TypeError – if byte_string is not a byte str type
Returns
string containing a guess at the encoding of byte_string. This is
appropriate to pass as the encoding argument when encoding and decoding
unicode strings.
We start by attempting to decode the byte str as UTF-8. If this succeeds we tell
the world it’s UTF-8 text. If it doesn’t and chardet is installed on the system
and disable_chardet is False this function will use it to try detecting the
encoding of byte_string. If it is not installed or chardet cannot determine the
encoding with a high enough confidence then we rather arbitrarily claim that it is
latin-1. Since latin-1 will encode to every byte, decoding from latin-1 to unicode
will not cause UnicodeErrors although the output might be mangled.
kitchen.text.misc.html_entities_unescape(string)
Substitute unicode characters for HTML entities
Parameters
string – unicode string to substitute out html entities
Raises TypeError – if something other than a unicode string is given
Return type
unicode string
Returns
The plain text without html entities
kitchen.text.misc.isbasestring(obj)
Determine if obj is a byte str or unicode string
In python2 this is eqiuvalent to isinstance(obj, basestring). In python3 it checks
whether the object is an instance of str, bytes, or bytearray. This is an aid to
porting code that needed to test whether an object was derived from basestring in
python2 (commonly used in unicode-bytes conversion functions)
Parameters
obj – Object to test
Returns
True if the object is a basestring. Otherwise False.
New in version Kitchen:: 1.2.0, API kitchen.text 2.2.0
kitchen.text.misc.isbytestring(obj)
Determine if obj is a byte str
In python2 this is equivalent to isinstance(obj, str). In python3 it checks
whether the object is an instance of bytes or bytearray.
Parameters
obj – Object to test
Returns
True if the object is a byte str. Otherwise, False.
New in version Kitchen:: 1.2.0, API kitchen.text 2.2.0
kitchen.text.misc.isunicodestring(obj)
Determine if obj is a unicode string
In python2 this is equivalent to isinstance(obj, unicode). In python3 it checks
whether the object is an instance of str.
Parameters
obj – Object to test
Returns
True if the object is a unicode string. Otherwise, False.
New in version Kitchen:: 1.2.0, API kitchen.text 2.2.0
kitchen.text.misc.process_control_chars(string, strategy='replace')
Look for and transform control characters in a string
Parameters
• string – string to search for and transform control characters within
• strategy –
XML does not allow ASCII control characters. When we encounter those we
need to know what to do. Valid options are:
replace
(default) Replace the control characters with "?"
ignore Remove the characters altogether from the output
strict Raise a ControlCharError when we encounter a control character
Raises
• TypeError – if string is not a unicode string.
• ValueError – if the strategy is not one of replace, ignore, or strict.
• kitchen.text.exceptions.ControlCharError – if the strategy is strict and a
control character is present in the string
Returns
unicode string with no control characters in it.
Changed in version kitchen: 1.2.0, API: kitchen.text 2.2.0 Strip out the C1 control
characters in addition to the C0 control characters.
kitchen.text.misc.str_eq(str1, str2, encoding='utf-8', errors='replace')
Compare two strings, converting to byte str if one is unicode
Parameters
• str1 – First string to compare
• str2 – Second string to compare
• encoding – If we need to convert one string into a byte str to compare,
the encoding to use. Default is utf-8.
• errors – What to do if we encounter errors when encoding the string. See
the kitchen.text.converters.to_bytes() documentation for possible values.
The default is replace.
This function prevents UnicodeError (python-2.4 or less) and UnicodeWarning (python
2.5 and higher) when we compare a unicode string to a byte str. The errors
normally arise because the conversion is done to ASCII. This function lets you
convert to utf-8 or another encoding instead.
NOTE:
When we need to convert one of the strings from unicode in order to compare them
we convert the unicode string into a byte str. That means that strings can
compare differently if you use different encodings for each.
Note that str1 == str2 is faster than this function if you can accept the following
limitations:
• Limited to python-2.5+ (otherwise a UnicodeDecodeError may be thrown)
• Will generate a UnicodeWarning if non-ASCII byte str is compared to unicode
string.
UTF-8
Functions for operating on byte str encoded as UTF-8
NOTE:
In many cases, it is better to convert to unicode, operate on the strings, then convert
back to UTF-8. unicode type can handle many of these functions itself. For those that
it doesn’t (removing control characters from length calculations, for instance) the
code to do so with a unicode type is often simpler.
WARNING:
All of the functions in this module are deprecated. Most of them have been replaced
with functions that operate on unicode values in kitchen.text.display.
kitchen.text.utf8.utf8_valid() has been replaced with a function in kitchen.text.misc.
kitchen.text.utf8.utf8_text_fill(text, *args, **kwargs)
Deprecated Similar to textwrap.fill() but understands utf-8 strings and doesn’t
screw up lists/blocks/etc.
Use kitchen.text.display.fill() instead.
kitchen.text.utf8.utf8_text_wrap(text, width=70, initial_indent='', subsequent_indent='')
Deprecated Similar to textwrap.wrap() but understands utf-8 data and doesn’t screw
up lists/blocks/etc
Use kitchen.text.display.wrap() instead
kitchen.text.utf8.utf8_valid(msg)
Deprecated Detect if a string is valid utf-8
Use kitchen.text.misc.byte_string_valid_encoding() instead.
kitchen.text.utf8.utf8_width(msg)
Deprecated Get the textual width of a utf-8 string
Use kitchen.text.display.textual_width() instead.
kitchen.text.utf8.utf8_width_chop(msg, chop=None)
Deprecated Return a string chopped to a given textual width
Use textual_width_chop() and textual_width() instead:
>>> msg = 'く ku ら ra と to み mi'
>>> # Old way:
>>> utf8_width_chop(msg, 5)
(5, 'く ku')
>>> # New way
>>> from kitchen.text.converters import to_bytes
>>> from kitchen.text.display import textual_width, textual_width_chop
>>> (textual_width(msg), to_bytes(textual_width_chop(msg, 5)))
(5, 'く ku')
kitchen.text.utf8.utf8_width_fill(msg, fill, chop=None, left=True, prefix='', suffix='')
Deprecated Pad a utf-8 string to fill a specified width
Use byte_string_textual_width_fill() instead
converters
deals with converting text for different encodings and to and from XML
display
deals with issues with printing text to a screen
misc is a catchall for text manipulation functions that don’t seem to fit elsewhere
utf8 contains deprecated functions to manipulate utf8 byte strings
Kitchen.collections
StrictDict
kitchen.collections.StrictDict provides a dictionary that treats str and unicode as
distinct key values.
class kitchen.collections.strictdict.StrictDict
Map class that considers unicode and str different keys
Ordinarily when you are dealing with a dict keyed on strings you want to have keys
that have the same characters end up in the same bucket even if one key is unicode
and the other is a byte str. The normal dict type does this for ASCII characters
(but not for anything outside of the ASCII range.)
Sometimes, however, you want to keep the two string classes strictly separate, for
instance, if you’re creating a single table that can map from unicode characters to
str characters and vice versa. This class will help you do that by making all
unicode keys evaluate to a different key than all str keys.
SEE ALSO:
dict for documentation on this class’s methods. This class implements all the
standard dict methods. Its treatment of unicode and str keys as separate
is the only difference.
Kitchen.iterutils Module
Functions to manipulate iterables
New in version Kitchen:: 0.2.1a1
Module author: Toshio Kuratomi <toshio@fedoraproject.org>
Module author: Luke Macken <lmacken@redhat.com>
kitchen.iterutils.isiterable(obj, include_string=False)
Check whether an object is an iterable
Parameters
• obj – Object to test whether it is an iterable
• include_string – If True and obj is a byte str or unicode string this
function will return True. If set to False, byte str and unicode strings
will cause this function to return False. Default False.
Returns
True if obj is iterable, otherwise False.
kitchen.iterutils.iterate(obj, include_string=False)
Generator that can be used to iterate over anything
Parameters
• obj – The object to iterate over
• include_string – if True, treat strings as iterables. Otherwise treat
them as a single scalar value. Default False
This function will create an iterator out of any scalar or iterable. It is useful
for making a value given to you an iterable before operating on it. Iterables have
their items returned. scalars are transformed into iterables. A string is treated
as a scalar value unless the include_string parameter is set to True. Example
usage:
>>> list(iterate(None))
[None]
>>> list(iterate([None]))
[None]
>>> list(iterate([1, 2, 3]))
[1, 2, 3]
>>> list(iterate(set([1, 2, 3])))
[1, 2, 3]
>>> list(iterate(dict(a='1', b='2')))
['a', 'b']
>>> list(iterate(1))
[1]
>>> list(iterate(iter([1, 2, 3])))
[1, 2, 3]
>>> list(iterate('abc'))
['abc']
>>> list(iterate('abc', include_string=True))
['a', 'b', 'c']
Helpers for versioning software
PEP-386 compliant versioning
PEP 386 defines a standard format for version strings. This module contains a function
for creating strings in that format.
kitchen.versioning.version_tuple_to_string(version_info)
Return a PEP 386 version string from a PEP 386 style version tuple
Parameters
version_info – Nested set of tuples that describes the version. See below
for an example.
Returns
a version string
This function implements just enough of PEP 386 to satisfy our needs. PEP 386
defines a standard format for version strings and refers to a function that will be
merged into the python standard library that transforms a tuple of version
information into a standard version string. This function is an implementation of
that function. Once that function becomes available in the python standard library
we will start using it and deprecate this function.
version_info takes the form that PEP 386’s NormalizedVersion.from_parts() uses:
((Major, Minor, [Micros]), [(Alpha/Beta/rc marker, version)],
[(post/dev marker, version)])
Ex: ((1, 0, 0), ('a', 2), ('dev', 3456))
It generates a PEP 386 compliant version string:
N.N[.N]+[{a|b|c|rc}N[.N]+][.postN][.devN]
Ex: 1.0.0a2.dev3456
WARNING:
This function does next to no error checking. It’s up to the person defining
the version tuple to make sure that the values make sense. If the PEP 386
compliant version parser doesn’t get released soon we’ll look at making this
function check that the version tuple makes sense before transforming it into a
string.
It’s recommended that you use this function to keep a __version_info__ tuple and
__version__ string in your modules. Why do we need both a tuple and a string? The
string is often useful for putting into human readable locations like release
announcements, version strings in tarballs, etc. Meanwhile the tuple is very easy
for a computer to compare. For example, kitchen sets up its version information
like this:
from kitchen.versioning import version_tuple_to_string
__version_info__ = ((0, 2, 1),)
__version__ = version_tuple_to_string(__version_info__)
Other programs that depend on a kitchen version between 0.2.1 and 0.3.0 can find
whether the present version is okay with code like this:
from kitchen import __version_info__, __version__
if __version_info__ < ((0, 2, 1),) or __version_info__ >= ((0, 3, 0),):
print 'kitchen is present but not at the right version.'
print 'We need at least version 0.2.1 and less than 0.3.0'
print 'Currently found: kitchen-%s' % __version__
Exceptions
Kitchen has a hierarchy of exceptions that should make it easy to catch many errors
emitted by kitchen itself.
Base kitchen exceptions
Exception classes for kitchen and the root of the exception hierarchy for all kitchen
modules.
exception kitchen.exceptions.KitchenError
Base exception class for any error thrown directly by kitchen.
Kitchen.text exceptions
Exception classes thrown by kitchen’s text processing routines.
exception kitchen.text.exceptions.XmlEncodeError
Exception thrown by error conditions when encoding an xml string.
exception kitchen.text.exceptions.ControlCharError
Exception thrown when an ascii control character is encountered.
1.0.0 Porting Guide
The 0.1 through 1.0.0 releases focused on bringing in functions from yum and
python-fedora. This porting guide tells how to port from those APIs to their kitchen
replacements.
python-fedora
┌──────────────────────────────┬──────────────────────────────────────┐
│python-fedora │ kitchen replacement │
├──────────────────────────────┼──────────────────────────────────────┤
│fedora.iterutils.isiterable() │ kitchen.iterutils.isiterable() │
│ │ [1] │
├──────────────────────────────┼──────────────────────────────────────┤
│fedora.textutils.to_unicode() │ kitchen.text.converters.to_unicode() │
├──────────────────────────────┼──────────────────────────────────────┤
│fedora.textutils.to_bytes() │ kitchen.text.converters.to_bytes() │
└──────────────────────────────┴──────────────────────────────────────┘
[1] isiterable() has changed slightly in kitchen. The include_string attribute has
switched its default value from True to False. So you need to change code like:
>>> # Old code
>>> isiterable('abcdef')
True
>>> # New code
>>> isiterable('abcdef', include_string=True)
True
yum
┌────────────────────────────┬────────────────────────────────────────────────┐
│yum │ kitchen replacement │
├────────────────────────────┼────────────────────────────────────────────────┤
│yum.i18n.dummy_wrapper() │ kitchen.i18n.DummyTranslations.ugettext() │
│ │ [2] │
├────────────────────────────┼────────────────────────────────────────────────┤
│yum.i18n.dummyP_wrapper() │ kitchen.i18n.DummyTanslations.ungettext() │
│ │ [2] │
├────────────────────────────┼────────────────────────────────────────────────┤
│yum.i18n.utf8_width() │ kitchen.text.display.textual_width() │
├────────────────────────────┼────────────────────────────────────────────────┤
│yum.i18n.utf8_width_chop() │ kitchen.text.display.textual_width_chop() │
│ │ and kitchen.text.display.textual_width() │
│ │ [3] [5] │
├────────────────────────────┼────────────────────────────────────────────────┤
│yum.i18n.utf8_valid() │ kitchen.text.misc.byte_string_valid_encoding() │
├────────────────────────────┼────────────────────────────────────────────────┤
│yum.i18n.utf8_text_wrap() │ kitchen.text.display.wrap() [4] │
├────────────────────────────┼────────────────────────────────────────────────┤
│yum.i18n.utf8_text_fill() │ kitchen.text.display.fill() [4] │
├────────────────────────────┼────────────────────────────────────────────────┤
│yum.i18n.to_unicode() │ kitchen.text.converters.to_unicode() [6] │
├────────────────────────────┼────────────────────────────────────────────────┤
│yum.i18n.to_unicode_maybe() │ kitchen.text.converters.to_unicode() [6] │
├────────────────────────────┼────────────────────────────────────────────────┤
│yum.i18n.to_utf8() │ kitchen.text.converters.to_bytes() [6] │
├────────────────────────────┼────────────────────────────────────────────────┤
│yum.i18n.to_str() │ kitchen.text.converters.to_unicode() or │
│ │ kitchen.text.converters.to_bytes() [7] │
├────────────────────────────┼────────────────────────────────────────────────┤
│yum.i18n.str_eq() │ kitchen.text.misc.str_eq() │
├────────────────────────────┼────────────────────────────────────────────────┤
│yum.misc.to_xml() │ kitchen.text.converters.unicode_to_xml() or │
│ │ kitchen.text.converters.byte_string_to_xml() │
│ │ [8] │
├────────────────────────────┼────────────────────────────────────────────────┤
│yum.i18n._() │ See: Initializing Yum i18n │
├────────────────────────────┼────────────────────────────────────────────────┤
│yum.i18n.P_() │ See: Initializing Yum i18n │
├────────────────────────────┼────────────────────────────────────────────────┤
│yum.i18n.exception2msg() │ kitchen.text.converters.exception_to_unicode() │
│ │ or kitchen.text.converter.exception_to_bytes() │
│ │ [9] │
└────────────────────────────┴────────────────────────────────────────────────┘
[2] These yum methods provided fallback support for gettext functions in case either
gaftonmode was set or gettext failed to return an object. In kitchen, we can use the
kitchen.i18n.DummyTranslations object to fulfill that role. Please see Initializing
Yum i18n for more suggestions on how to do this.
[3] The yum version of these functions returned a byte str. The kitchen version listed
here returns a unicode string. If you need a byte str simply call
kitchen.text.converters.to_bytes() on the result.
[4] The yum version of these functions would return either a byte str or a unicode string
depending on what the input value was. The kitchen version always returns unicode
strings.
[5] yum.i18n.utf8_width_chop() performed two functions. It returned the piece of the
message that fit in a specified width and the width of that message. In kitchen, you
need to call two functions, one for each action:
>>> # Old way
>>> utf8_width_chop(msg, 5)
(5, 'く ku')
>>> # New way
>>> from kitchen.text.display import textual_width, textual_width_chop
>>> (textual_width(msg), textual_width_chop(msg, 5))
(5, u'く ku')
[6] If the yum version of to_unicode() or to_utf8() is given an object that is not a
string, it returns the object itself. kitchen.text.converters.to_unicode() and
kitchen.text.converters.to_bytes() default to returning the simplerepr of the object
instead. If you want the yum behaviour, set the nonstring parameter to passthru:
>>> from kitchen.text.converters import to_unicode
>>> to_unicode(5)
u'5'
>>> to_unicode(5, nonstring='passthru')
5
[7] yum.i18n.to_str() could return either a byte str. or a unicode string In kitchen you
can get the same effect but you get to choose whether you want a byte str or a
unicode string. Use to_bytes() for str and to_unicode() for unicode.
[8] yum.misc.to_xml() was buggy as written. I think the intention was for you to be able
to pass a byte str or unicode string in and get out a byte str that was valid to use
in an xml file. The two kitchen functions byte_string_to_xml() and unicode_to_xml()
do that for each string type.
[9] When porting yum.i18n.exception2msg() to use kitchen, you should setup two wrapper
functions to aid in your port. They’ll look like this:
from kitchen.text.converters import EXCEPTION_CONVERTERS, \
BYTE_EXCEPTION_CONVERTERS, exception_to_unicode, \
exception_to_bytes
def exception2umsg(e):
'''Return a unicode representation of an exception'''
c = [lambda e: e.value]
c.extend(EXCEPTION_CONVERTERS)
return exception_to_unicode(e, converters=c)
def exception2bmsg(e):
'''Return a utf8 encoded str representation of an exception'''
c = [lambda e: e.value]
c.extend(BYTE_EXCEPTION_CONVERTERS)
return exception_to_bytes(e, converters=c)
The reason to define this wrapper is that many of the exceptions in yum put the message in
the value attribute of the Exception instead of adding it to the args attribute. So the
default EXCEPTION_CONVERTERS don’t know where to find the message. The wrapper tells
kitchen to check the value attribute for the message. The reason to define two wrappers
may be less obvious. yum.i18n.exception2msg() can return a unicode string or a byte str
depending on a combination of what attributes are present on the Exception and what locale
the function is being run in. By contrast, kitchen.text.converters.exception_to_unicode()
only returns unicode strings and kitchen.text.converters.exception_to_bytes() only returns
byte str. This is much safer as it keeps code that can only handle unicode or only handle
byte str correctly from getting the wrong type when an input changes but it means you need
to examine the calling code when porting from yum.i18n.exception2msg() and use the
appropriate wrapper.
Initializing Yum i18n
Previously, yum had several pieces of code to initialize i18n. From the toplevel of
yum/i18n.py:
try:.
'''
Setup the yum translation domain and make _() and P_() translation wrappers
available.
using ugettext to make sure translated strings are in Unicode.
'''
import gettext
t = gettext.translation('yum', fallback=True)
_ = t.ugettext
P_ = t.ungettext
except:
'''
Something went wrong so we make a dummy _() wrapper there is just
returning the same text
'''
_ = dummy_wrapper
P_ = dummyP_wrapper
With kitchen, this can be changed to this:
from kitchen.i18n import easy_gettext_setup, DummyTranslations
try:
_, P_ = easy_gettext_setup('yum')
except:
translations = DummyTranslations()
_ = translations.ugettext
P_ = translations.ungettext
NOTE:
In overcoming-frustration, it is mentioned that for some things (like exception
messages), using the byte str oriented functions is more appropriate. If this is
desired, the setup portion is only a second call to kitchen.i18n.easy_gettext_setup():
b_, bP_ = easy_gettext_setup('yum', use_unicode=False)
The second place where i18n is setup is in yum.YumBase._getConfig() in yum/__init_.py if
gaftonmode is in effect:
if startupconf.gaftonmode:
global _
_ = yum.i18n.dummy_wrapper
This can be changed to:
if startupconf.gaftonmode:
global _
_ = DummyTranslations().ugettext()
Conventions for contributing to kitchen
Style
• Strive to be PEP 8 compliant
• Run :command:`pylint ` over the code and try to resolve most of its nitpicking
Python 2.4 compatibility
At the moment, we’re supporting python-2.4 and above. Understand that there’s a lot of
python features that we cannot use because of this.
Sometimes modules in the python standard library can be added to kitchen so that they’re
available. When we do that we need to be careful of several things:
1. Keep the module in sync with the version in the python-2.x trunk. Use
maintainers/sync-copied-files.py for this.
2. Sync the unittests as well as the module.
3. Be aware that not all modules are written to remain compatible with Python-2.4 and
might use python language features that were not present then (generator expressions,
relative imports, decorators, with, try: with both except: and finally:, etc) These
are not good candidates for importing into kitchen as they require more work to keep
synced.
Unittests
• At least smoketest your code (make sure a function will return expected values for one
set of inputs).
• Note that even 100% coverage is not a guarantee of working code! Good tests will
realize that you need to also give multiple inputs that test the code paths of called
functions that are outside of your code. Example:
def to_unicode(msg, encoding='utf8', errors='replace'):
return unicode(msg, encoding, errors)
# Smoketest only. This will give 100% coverage for your code (it
# tests all of the code inside of to_unicode) but it leaves a lot of
# room for errors as it doesn't test all combinations of arguments
# that are then passed to the unicode() function.
tools.ok_(to_unicode('abc') == u'abc')
# Better -- tests now cover non-ascii characters and that error conditions
# occur properly. There's a lot of other permutations that can be
# added along these same lines.
tools.ok_(to_unicode(u'café', 'utf8', 'replace'))
tools.assert_raises(UnicodeError, to_unicode, [u'cafè ñunru'.encode('latin1')])
• We’re using nose for unittesting. Rather than depend on unittest2 functionality, use
the functions that nose provides.
• Remember to maintain python-2.4 compatibility even in unittests.
Docstrings and documentation
We use sphinx to build our documentation. We use the sphinx autodoc extension to pull
docstrings out of the modules for API documentation. This means that docstrings for
subpackages and modules should follow a certain pattern. The general structure is:
• Introductory material about a module in the module’s top level docstring.
• Introductory material should begin with a level two title: an overbar and underbar of
‘-‘.
• docstrings for every function.
• The first line is a short summary of what the function does
• This is followed by a blank line
• The next lines are a field list
<http://sphinx.pocoo.org/markup/desc.html#info-field-lists>_ giving information about
the function’s signature. We use the keywords: arg, kwarg, raises, returns, and
sometimes rtype. Use these to describe all arguments, key word arguments, exceptions
raised, and return values using these.
• Parameters that are kwarg should specify what their default behaviour is.
Kitchen versioning
Currently the kitchen library is in early stages of development. While we’re in this
state, the main kitchen library uses the following pattern for version information:
•
Versions look like this::
__version_info__ = ((0, 1, 2),) __version__ = ‘0.1.2’
• The Major version number remains at 0 until we decide to make the first 1.0 release of
kitchen. At that point, we’re declaring that we have some confidence that we won’t need
to break backwards compatibility for a while.
• The Minor version increments for any backwards incompatible API changes. When this is
updated, we reset micro to zero.
• The Micro version increments for any other changes (backwards compatible API changes,
pure bugfixes, etc).
NOTE:
Versioning is only updated for releases that generate sdists and new uploads to the
download directory. Usually we update the version information for the library just
before release. By contrast, we update kitchen Versioning when an API change is made.
When in doubt, look at the version information in the last release.
I18N
All strings that are used as feedback for users need to be translated. kitchen sets up
several functions for this. _() is used for marking things that are shown to users via
print, GUIs, or other “standard” methods. Strings for exceptions are marked with b_().
This function returns a byte str which is needed for use with exceptions:
from kitchen import _, b_
def print_message(msg, username):
print _('%(user)s, your message of the day is: %(message)s') % {
'message': msg, 'user': username}
raise Exception b_('Test message')
This serves several purposes:
• It marks the strings to be extracted by an xgettext-like program.
• _() is a function that will substitute available translations at runtime.
NOTE:
By using the %()s with dict style of string formatting, we make this string friendly to
translators that may need to reorder the variables when they’re translating the string.
paver <http://www.blueskyonmars.com/projects/paver/>_ and babel
<http://babel.edgewall.org/>_ are used to extract the strings.
API updates
Kitchen strives to have a long deprecation cycle so that people have time to switch away
from any APIs that we decide to discard. Discarded APIs should raise a DeprecationWarning
and clearly state in the warning message and the docstring how to convert old code to use
the new interface. An example of deprecating a function:
import warnings
from kitchen import _
from kitchen.text.converters import to_bytes, to_unicode
from kitchen.text.new_module import new_function
def old_function(param):
'''**Deprecated**
This function is deprecated. Use
:func:`kitchen.text.new_module.new_function` instead. If you want
unicode strngs as output, switch to::
>>> from kitchen.text.new_module import new_function
>>> output = new_function(param)
If you want byte strings, use::
>>> from kitchen.text.new_module import new_function
>>> from kitchen.text.converters import to_bytes
>>> output = to_bytes(new_function(param))
'''
warnings.warn(_('kitchen.text.old_function is deprecated. Use'
' kitchen.text.new_module.new_function instead'),
DeprecationWarning, stacklevel=2)
as_unicode = isinstance(param, unicode)
message = new_function(to_unicode(param))
if not as_unicode:
message = to_bytes(message)
return message
If a particular API change is very intrusive, it may be better to create a new version of
the subpackage and ship both the old version and the new version.
NEWS file
Update the NEWS file when you make a change that will be visible to the users. This is
not a ChangeLog file so we don’t need to list absolutely everything but it should give the
user an idea of how this version differs from prior versions. API changes should be
listed here explicitly. bugfixes can be more general:
-----
0.2.0
-----
* Relicense to LGPLv2+
* Add kitchen.text.format module with the following functions:
textual_width, textual_width_chop.
* Rename the kitchen.text.utils module to kitchen.text.misc. use of the
old names is deprecated but still available.
* bugfixes applied to kitchen.pycompat24.defaultdict that fixes some
tracebacks
Kitchen subpackages
Kitchen itself is a namespace. The kitchen sdist (tarball) provides certain useful
subpackages.
SEE ALSO:
Kitchen addon packages
For information about subpackages not distributed in the kitchen sdist that
install into the kitchen namespace.
Versioning
Each subpackage should have its own version information which is independent of the other
kitchen subpackages and the main kitchen library version. This is used so that code that
depends on kitchen APIs can check the version information. The standard way to do this is
to put something like this in the subpackage’s __init__.py:
from kitchen.versioning import version_tuple_to_string
__version_info__ = ((1, 0, 0),)
__version__ = version_tuple_to_string(__version_info__)
__version_info__ is documented in kitchen.versioning. The values of the first tuple
should describe API changes to the module. There are at least three numbers present in
the tuple: (Major, minor, micro). The major version number is for backwards incompatible
changes (For instance, removing a function, or adding a new mandatory argument to a
function). Whenever one of these occurs, you should increment the major number and reset
minor and micro to zero. The second number is the minor version. Anytime new but
backwards compatible changes are introduced this number should be incremented and the
micro version number reset to zero. The micro version should be incremented when a change
is made that does not change the API at all. This is a common case for bugfixes, for
instance.
Version information beyond the first three parts of the first tuple may be useful for
versioning but semantically have similar meaning to the micro version.
NOTE:
We update the __version_info__ tuple when the API is updated. This way there’s less
chance of forgetting to update the API version when a new release is made. However, we
try to only increment the version numbers a single step for any release. So if
kitchen-0.1.0 has kitchen.text.__version__ == ‘1.0.1’, kitchen-0.1.1 should have
kitchen.text.__version__ == ‘1.0.2’ or ‘1.1.0’ or ‘2.0.0’.
Criteria for subpackages in kitchen
Subpackages within kitchen should meet these criteria:
• Generally useful or needed for other pieces of kitchen.
• No mandatory requirements outside of the python standard library.
• Optional requirements from outside the python standard library are allowed. Things
with mandatory requirements are better placed in kitchen addon packages
• Somewhat API stable – this is not a hard requirement. We can change the kitchen api.
However, it is better not to as people may come to depend on it.
SEE ALSO:
API Updates
Kitchen addon packages
Addon packages are very similar to subpackages integrated into the kitchen sdist. This
section just lists some of the differences to watch out for.
setup.py
Your setup.py should contain entries like this:
# It's suggested to use a dotted name like this so the package is easily
# findable on pypi:
setup(name='kitchen.config',
# Include kitchen in the keywords, again, for searching on pypi
keywords=['kitchen', 'configuration'],
# This package lives in the directory kitchen/config
packages=['kitchen.config'],
# [...]
)
Package directory layout
Create a kitchen directory in the toplevel. Place the addon subpackage in there. For
example:
./ <== toplevel with README, setup.py, NEWS, etc
kitchen/
kitchen/__init__.py
kitchen/config/ <== subpackage directory
kitchen/config/__init__.py
Fake kitchen module
The :file::__init__.py in the kitchen directory is special. It won’t be installed. It
just needs to pull in the kitchen from the system so that you are able to test your
module. You should be able to use this boilerplate:
# Fake module. This is not installed, It's just made to import the real
# kitchen modules for testing this module
import pkgutil
# Extend the __path__ with everything in the real kitchen module
__path__ = pkgutil.extend_path(__path__, __name__)
NOTE:
kitchen needs to be findable by python for this to work. Installed in the
site-packages directory or adding it to the PYTHONPATH will work.
Your unittests should now be able to find both your submodule and the main kitchen module.
Versioning
It is recommended that addon packages version similarly to Versioning. The
__version_info__ and __version__ strings can be changed independently of the version
exposed by setup.py so that you have both an API version (__version_info__) and release
version that’s easier for people to parse. However, you aren’t required to do this and
you could follow a different methodology if you want (for instance, Kitchen versioning)
Glossary
“Everything but the kitchen sink”
An English idiom meaning to include nearly everything that you can think of.
API version
Version that is meant for computer consumption. This version is parsable and
comparable by computers. It contains information about a library’s API so that
computer software can decide whether it works with the software.
ASCII A character encoding that maps numbers to characters essential to American English.
It maps 128 characters using 7bits.
SEE ALSO:
http://en.wikipedia.org/wiki/ASCII
ASCII compatible
An encoding in which the particular byte that maps to a character in the ASCII
character set is only used to map to that character. This excludes EBDIC based
encodings and many multi-byte fixed and variable width encodings since they reuse
the bytes that make up the ASCII encoding for other purposes. UTF-8 is notable as
a variable width encoding that is ASCII compatible.
SEE ALSO:
http://en.wikipedia.org/wiki/Variable-width_encoding
For another explanation of various ways bytes are mapped to characters in
a possibly incompatible manner.
code points
code point
code point
A number that maps to a particular abstract character. Code points make it so that
we have a number pointing to a character without worrying about implementation
details of how those numbers are stored for the computer to read. Encodings define
how the code points map to particular sequences of bytes on disk and in memory.
control characters
control character
control character
The set of characters in unicode that are used, not to display glyphs on the
screen, but to tell the display in program to do something.
SEE ALSO:
http://en.wikipedia.org/wiki/Control_character
grapheme
characters or pieces of characters that you might write on a page to make words,
sentences, or other pieces of text.
SEE ALSO:
http://en.wikipedia.org/wiki/Grapheme
I18N I18N is an abbreviation for internationalization. It’s often used to signify the
need to translate words, number and date formats, and other pieces of data in a
computer program so that it will work well for people who speak another language
than yourself.
message catalogs
message catalog
message catalog
Message catalogs contain translations for user-visible strings that are present in
your code. Normally, you need to mark the strings to be translated by wrapping
them in one of several gettext functions. The function serves two purposes:
1. It allows automated tools to find which strings are supposed to be extracted for
translation.
2. The functions perform the translation when the program is running.
SEE ALSO:
babel’s documentation
for one method of extracting message catalogs from source code.
Murphy’s Law
“Anything that can go wrong, will go wrong.”
SEE ALSO:
http://en.wikipedia.org/wiki/Murphy%27s_Law
release version
Version that is meant for human consumption. This version is easy for a human to
look at to decide how a particular version relates to other versions of the
software.
textual width
The amount of horizontal space a character takes up on a monospaced screen. The
units are number of character cells or columns that it takes the place of.
UTF-8 A character encoding that maps all unicode code points to a sequence of bytes. It
is compatible with ASCII. It uses a variable number of bytes to encode all of
unicode. ASCII characters take one byte. Characters from other parts of unicode
take two to four bytes. It is widespread as an encoding on the internet and in
Linux.
INDICES AND TABLES
• genindex
• modindex
• search
PROJECT PAGES
More information about the project can be found on the project webpage
The latest published version of this documentation can be found on the documentation page
COPYRIGHT
2017 Red Hat, Inc. and others