Provided by: libinline-python-perl_0.57-1build1_amd64 
NAME
Inline::Python - Write Perl subs and classes in Python.
SYNOPSIS
print "9 + 16 = ", add(9, 16), "\n";
print "9 - 16 = ", subtract(9, 16), "\n";
use Inline Python => <<'END_OF_PYTHON_CODE';
def add(x,y):
return x + y
def subtract(x,y):
return x - y
END_OF_PYTHON_CODE
DESCRIPTION
The "Inline::Python" module allows you to put Python source code directly "inline" in a
Perl script or module. It sets up an in-process Python interpreter, runs your code, and
then examines Python's symbol table for things to bind to Perl. The process of
interrogating the Python interpreter for globals only occurs the first time you run your
Python code. The namespace is cached, and subsequent calls use the cached version.
This document describes "Inline::Python", the Perl package which gives you access to a
Python interpreter. For lack of a better place to keep it, it also gives you instructions
on how to use "perlmodule", the Python package which gives you access to the Perl
interpreter.
WHAT'S NEW?
Version 0.21 provides the ability to bind to 'new-style' classes (as defined by the python
PEP's 252 and 253.) See "New-Style Classes" for details.
See the Changes file for new features in recent versions.
Using the Inline::Python Module
Using Inline::Python will seem very similar to using another Inline language, thanks to
Inline's consistent look and feel.
This section will explain the different ways to use Inline::Python. For more details on
"Inline", see 'perldoc Inline'.
Giving Your Source to Inline
The most basic form for using "Inline::Python" is this:
use Inline Python => 'Python source code';
Of course, you can use Perl's "here document" style of quoting to make the code slightly
easier to read:
use Inline Python => <<'END';
Python source code goes here.
END
The source code can also be specified as a filename, a subroutine reference (sub routine
should return source code), or an array reference (array contains lines of source code).
The recommended way of using Inline is this:
use Inline Python;
...
__END__
__Python__
Python source code goes here.
This information is detailed in 'perldoc Inline'.
Importing Functions
Maybe you have a whole library written in Python that only needs one entry point. You'll
want to import that function. It's as easy as this:
use Inline Python;
doit();
__END__
__Python__
from mylibrary import doit
Inline::Python actually binds to every function in Python's "global" namespace (those of
you in the know, know that namespace is called '__main__'). So if you had another function
there, you'd get that too.
Importing Classes
If you've written a library in Python, you'll make it object-oriented. That's just
something Python folks do. So you'll probably want to import a class, not a function.
That's just as easy:
use Inline Python;
my $obj = new Myclass;
__END__
__Python__
from mylibrary import myclass as Myclass
New-Style Classes
As of python 2.2, the python internals have begun to change in a way which makes types
'look' more like classes. This means that your python code can now subclass builtin
python types such as lists, tuples, integers, and etc. It also means that identifying
python objects and creating Perl bindings for them has become a little trickier.
See Guido's write-up (http://www.python.org/2.2.2/descrintro.html) and the relevant Python
Enhancement Proposals (PEP) numbers 252 and 253 for details about the python code. Also,
see the mailing-list discussion
(http://mail.python.org/pipermail/python-dev/2004-July/046060.html) for possible
implications regarding C-language python extensions.
This change should not affect code which uses Inline::Python, except that it allows you to
bind to python classes which have been written using these new features. In most cases,
you will be importing an entire class from an external library as defined in the example
above.
In other cases, you may be writing Inline::Python code as follows:
use Inline Python => <<'END';
class Foo(object):
def __init__(self):
print "new Foo object being created"
self.data = {}
def get_data(self): return self.data
def set_data(self,dat):
self.data = dat
END
Additional caveats may exist. Note that if the python class is subclassing one of the
builtin types which would normally be accessible as a 'Perlish' translation, that the
instance will be an opaque object accessible only through its class methods.
# Class is defined as 'def Class(float):'
my $obj = Class->new(4);
print $$obj, "\n"; # will NOT print '4.0'
New-Style
Boundary Conditions
What if you have a class that wasn't imported? Can you deal with instances of that class
properly?
Of course you can! Check this out:
use Inline Python => <<END;
def Foo():
class Bar:
def __init__(self):
print "new Bar()"
def tank(self):
return 10
return Bar()
END
my $o = Foo();
print $o->tank(), "\n";
In this example, "Bar" isn't imported because it isn't a global -- it's hidden inside the
function Foo(). But Foo() is imported into Perl, and it returns an instance of the "Bar"
class. What happens then?
Whenever Inline::Python needs to return an instance of a class to Perl, it generates an
instance of Inline::Python::Object, the base class for all Inline::Python objects. This
base class knows how to do all the things you need: calling methods, in this case.
Exceptions
Exceptions thrown in Python code get translated to Perl exceptions which you can catch
using eval.
Boolean
Python supports a Boolean type and two constants False and True. If one of these is passed
from Python to Perl, the value is represented by an Inline::Python::Boolean object that
uses overload to behave like 1 or undef in boolean context in Perl. When this object is
passed back to Python, it is translated back to the False or True constant it originated
from.
To pass a Boolean value that originated from Perl to Python use the two constants
$Inline::Python::Boolean::true and $Inline::Python::Boolean::false if it is important that
the value is of type Boolean in Python.
Using Perl inside Python (inside Perl)
This section doesn't talk at all about "Inline::Python". It's about how to use "perl".
"perl" is a Python module bundled with Inline::Python that gives you access to Perl from
inside your Python code. In the future, it will be possible to compile Inline::Python to
work the other way around -- to use Python as the main programming language, and jump into
Perl when you want to.
The "perl" package exposes Perl packages and subs. It uses the same code as Inline::Python
to automatically translate parameters and return values as needed. Packages and subs are
represented as "PerlPkg" and "PerlSub", respectively.
Using the PerlPkg Type
The "perl" package is actually not a package at all. As soon as you import it, it replaces
itself with an instance of the PerlPkg class, wrapping the Perl package "main". Perl's
'main' package is analogous to '__main__' in Python.
Here's what you can do with the 'main' PerlPkg:
eval()
eval(source code)
Unlike Python, Perl has no exec() -- the eval() function always returns the result of the
code it evaluated. eval() takes exactly one argument, the perl source code, and returns
the result of the evaluation.
require() and use()
require(module name)
use(module name)
Use require() instead of "import". In Python, you'd say this:
import md5
But using the perl module, you'd say this:
perl.require("Digest::MD5")
Of course, in Perl there's more than one way to do it (TM). require() doesn't run the
package's import() function. If you want symbols exported, for instance, use use() instead
of require().
Here is the functionality common to all PerlPkg instances:
__getattr__
Python's __getattr__() function allows the package to dynamically return something to
satisfy the request. For instance, you can get at the subs in a perl package by using
dir() (which is the same as "getattr(perl, '__methods__')".
Here's an example:
perl.eval("sub f { 10 }") # define main::f
f = perl.f
f(); f("hello") # no argument checking
if perl.f() != 10:
import sys; sys.exit(1)
Notice what happens. First we call eval() to define a sub 'f'. Then we say "perl.f", which
goes into the __getattr__() method. We check the Perl namespace and see a function called
f, which we return, wrapped in an instance of the PerlSub type.
Accessing a perl object's data
__getattr__ may also be used to access a Perl object's attributes, just like Python
allows. The Perl object just has to implement a sub __getattr__ returning the requested
attribute, which may even be calculated on the fly.
An example for the common hash based objects:
sub __getattr__ {
my ($self, $attr) = @_;
return $self->{$attr};
}
This allows Python code to access the perl object's data like:
print my_perl_object.field_name
named arguments
When a Perl sub is called with named arguments from Python code, Inline::Python follows
the PyObject_Call protocol: positional arguments are given as array ref followed by named
arguments as a hash ref. A Perl method supporting named arguments would therefore look
like:
sub supports_named_arguments {
my ($self, $positional, $named) = @_;
foreach (qw( named1 named2 )) {
last unless @$positional;
$named->{$_} = shift @$positional;
}
...
}
If this method is called using only positional arguments, they would just be pushed into
@_ like in any other method, complicating it to:
sub supports_named_arguments {
my ($self, $positional, $named) = @_;
if (@_ == 3 and $size and ref $size and ref $size eq 'ARRAY' and ref $useimage eq 'HASH') { # called using named parameters
foreach (qw( named1 named2 ... )) {
last unless @$positional;
$named->{$_} = shift @$positional;
}
}
else {
$named = { named1 => $positional, named2 => $named, named3 => $_[3], ... };
}
...
}
As this adds a lot of boiler plate code to subroutines, it is better to just use Perl
named arguments conventions (single hashref parameter) if possible.
Using the PerlSub Type
All Perl subs are wrapped in the PerlSub type, so that they can emulate Python
subroutines. You can call them. It's all good. Here's what you can do with PerlSub
objects:
Call
PerlSub catches the call action and forwards the call to the real sub in Perl.
Set the evaluation flags
Perl has this notion of calling context. A subroutine can ask Perl what it is being used
for. The idea is that if no one cares about your return value, you might be able to save
time by not building it. By default, PerlSub objects evaluate in 'list' context with no
extra flags turned on.
perl.eval("sub f { 10 }")
f = perl.f
f.flags = f.flags | f.G_SCALAR
x = f()
Here are the most common flags you'll need. For more details about these and other
possible flags, see perlcall.
1. G_VOID
Calls the Perl subroutine in a void context. Guarantees that no results will be
returned. If any are returned, Perl deletes them.
2. G_SCALAR
Calls the Perl subroutine in a scalar context. Ensures that only one element is
returned from the sub. If the sub returns a list, only the last element is actually
saved.
3. G_ARRAY
Calls the Perl subroutine in a list context. Ensures that any items returned from the
subroutine are returned. This is the default for PerlSub objects.
4. G_DISCARD
If you are not interested in the return values, you can optimize slightly by telling
Perl, and it will discard all returned values for you.
5. G_NOARGS
If you are not passing any arguments, you can optimize the call so that Perl doesn't
bother setting up the stack for parameters.
6. G_EVAL
It is possible for the Perl sub to fail, either by calling die() explicitly or by
calling a non-existent sub. By default, the process will terminate immediately. To
avoid this happening, you can trap the exception using the G_EVAL flag.
Under the Hood
When Inline::Python imports a class or function, it creates subs in Perl which delegate
the action to some C functions I've written, which know how to call Python functions and
methods.
use Inline Python => <<'END';
class Foo:
def __init__(self):
print "new Foo object being created"
self.data = {}
def get_data(self): return self.data
def set_data(self,dat):
self.data = dat
END
Inline::Python actually generates this code and eval()s it:
package main::Foo;
@main::Foo::ISA = qw(Inline::Python::Object);
sub new {
splice @_, 1, 0, "__main__", "Foo";
return &Inline::Python::py_new_object;
}
sub set_data {
splice @_, 1, 0, "set_data";
return &Inline::Python::py_call_method;
}
sub get_data {
splice @_, 1, 0, "get_data";
return &Inline::Python::py_call_method;
}
sub __init__ {
splice @_, 1, 0, "__init__";
return &Inline::Python::py_call_method;
}
More about those "py_*" functions, and how to generate this snippet of code yourself, in
the next section.
The Do-it-yourselfer's Guide to Inline::Python
Sometimes you don't actually want to do things the Inline Way. Maybe you just want to use
a Python class as-is, without ever treating it like a normal Perl class:
use Inline::Python qw(py_eval);
py_eval(<<'END');
class MyClass:
def __init__(self): self.data = {}
def put(self, key, value): self.data[key] = value
def get(self, key):
try: return self.data[key]
except KeyError: return None
END
my $o = Inline::Python::Object->new('__main__', 'MyClass');
$o->put("candy", "yummy");
die "Ooops" unless $o->get("candy") eq 'yummy';
Inline::Python provides a full suite of exportable functions you can use to manipulate
Python objects and functions "directly".
py_eval()
py_eval("python source code", [context])
The new py_eval() behaves a little like Perl's eval(). It evaluates the code or croaks on
failure. The optional context argument can be used to place restrictions on the type of
code allowed, as well as influence what happens to the result.
0 Accepts only expressions. Complete statements yield a syntax error. An expression is
anything that can appear to the right of an '=' sign. Returns the value of the
expression.
1 The default. Accepts arbitrarily long input, which may be any valid Python code.
Always returns "undef".
2 Accepts exactly one statement, and prints the result to STDOUT. This is how Python
works in interactive mode. Always returns "undef".
py_call_function()
py_call_function("package", "function", args...)
This function runs a Python function and returns the result. The "package" and "function"
uniquely identify a function, and the remaining args are passed to the function.
Those who know Python well enough will know you can actually "run" a class and get an
instance of that class back. But in case that's just too weird for you, I've given you a
slightly higher-level wrapper around that common idiom.
py_new_object()
py_new_object("perl package", "python package",
"python class", args...)
This function creates an instance of a Python class. The "python class" is the name of the
class inside the "python package". The new object is blessed into the given "perl
package". The remaining args are passed directly to the constructor.
py_call_method()
py_call_method(object, "method name", args...)
Given an instance of a Python class, this function can call a method on it. This is useful
if you have an object which is blessed into a non-existent Perl package. Attempts to use
Perl's object syntax would fail, because Perl wouldn't find any methods in that package.
But py_call_method() can always perform method calls correctly since it unwraps the
underlying Python object.
eval_python()
Unlike in previous releases of Inline::Python, eval_python() can now return the result of
the code. As before, eval_python() is overloaded:
1. eval_python(code, [context])
Evaluate the code using py_eval().
2. eval_python(python package, function, args...)
Run the given function and return the results using py_call_function().
3. eval_python(object, method, args...)
Invoke the given method on the object using py_call_method() and return the results.
py_bind_func()
py_bind_func("symbol name", "python package", "function")
This function imports a Python function (named "function") as the symbol named by "perl
symbol". After this function has been called, the Python function can be called as if it
were a Perl function in the given package.
use Inline::Python qw(py_eval py_bind_func);
py_eval(<<'END');
def Foo():
return 42
END
# For the purposes of this example, so I know the package, I set it:
py_bind_func("main::Bar", "__main__", "Foo");
print "The meaning of life is: ", Bar(), "\n";
This call to py_bind_func() will generate this code and eval() it:
sub main::Bar {
unshift @_, "__main__", "Foo";
return &Inline::Python::py_call_function;
}
py_bind_class()
py_bind_class("perl package", "python package", "class", methods...)
This function imports a Python class (named "class") into the Perl package named by "perl
package". After this function has been called, the Perl package will look just like a
regular Perl class.
The example I showed earlier in the "Under the Hood" section shows the output of
py_bind_class. Here's another look at it:
use Inline::Python qw(py_eval py_bind_class);
py_eval(<<'END');
class Foo:
def __init__(self):
print "new Foo object being created"
self.data = {}
def get_data(self): return self.data
def set_data(self,dat):
self.data = dat
END
py_bind_class("main::Foo", "__main__", "Foo", "set_data", "get_data");
my $o = new Foo;
This call to py_bind_class() will generate this code and eval() it:
package main::Foo;
@main::Foo::ISA = qw(Inline::Python::Object);
sub new {
splice @_, 1, 0, "__main__", "Foo";
return &Inline::Python::py_new_object;
}
sub set_data {
splice @_, 1, 0, "set_data";
return &Inline::Python::py_call_method;
}
sub get_data {
splice @_, 1, 0, "get_data";
return &Inline::Python::py_call_method;
}
Note that if you want methods to be created as I've shown, you must pass them to
py_bind_class() yourself. It doesn't create anything except new() and the @ISA array. It
doesn't need to, since the base class knows how to deal with any method call -- but it's
also slower, since it has to walk up the inheritance tree to the AUTOLOAD method. I
recommend binding to the functions you know about, especially if you're the one writing
the code. If it's auto-generated, use py_study_package(), described below.
py_study_package()
py_study_package(["package"])
This function interrogates the Python interpreter about the given package (or '__main__'
if you don't specify one). It returns a list of key/value pairs, so it should be used like
this:
py_eval('import pickle');
my %namespace = py_study_package("pickle");
On my machine, %namespace looks something like this:
$VAR1 = {
'classes' => { ... },
'functions' => [
'_keep_alive',
'loads',
'dump',
'load',
'dumps',
'test',
'whichmodule'
]
};
Each result can be fed to py_bind_function() and py_bind_class(), which is exactly what
Inline::Python itself does.
py_is_tuple()
my $array_ref = py_eval('(1, 2)')
$is_tuple = py_is_tuple($array_ref)
This function can tell you if the array reference you got from calling some Python code
was a tuple in Python or not (e.g. a normal array). This can be useful if an API requires
a distinction between those cases. py_is_tuple works by looking for a magic marker put
onto array refs by Py2Pl. Bear in mind that this marker may get lost when copying the
array data.
SEE ALSO
For information about using "Inline", see Inline.
For information about other Inline languages, see Inline-Support.
Inline::Python's mailing list is inline@perl.org
To subscribe, send email to inline-subscribe@perl.org
BUGS AND DEFICIENCIES
This is a production quality release of Inline::Python. It is fairly feature complete and
runs stable with no known crasher bugs or memory leaks. Further testing and expanded
support for other operating systems and platforms will be a focus for future releases.
When reporting a bug, please do the following:
- Put "use Inline REPORTBUG;" at the top of your code, or
use the command line option "perl -MInline=REPORTBUG ...".
- Run your code.
- Follow the printed instructions.
Here are some things to watch out for:
1. Note that the namespace imported into Perl is NOT recursively traversed. Only Python
globals are imported into Perl -- subclasses, subfunctions, and other modules are not
imported.
Example:
use Inline Python => <<'END';
import mymodule
class A:
class B: pass
END
The namespace imported into perl is ONLY that related to "A". Nothing related to
"mymodule" or "B" is imported, unless some Python code explicitly copies variables
from the mymodule namespace into the global namespace before Perl binds to it.
SUPPORTED PLATFORMS
Inline::Python has been tested on RedHat Linux 6.2 with a variety of different Perl and
Python configurations. It also seems to be running pretty well on openSUSE at least from
10.3 to 13.1 and on Solaris. Previous versions of Inline::Python worked on Windows and
Cygwin -- this version has never been tested there. I strongly suspect it will require
patching. Please send me patches.
This version of Inline::Python has been tested with Python versions from 2.5 to 2.7 and
from 3.1 to 3.4.
PORTING YOUR INLINE PYTHON CODE FROM 2 TO 3
First of all, follow the Python guide from 2 to 3:
https://docs.python.org/3/howto/pyporting.html
For Perl integration:
- Non-utf8-flagged Perl strings will be Python bytes, utf8-flagged Perl strings will be Python string
- __cmp__ is no more supported in Python 3 and has been replaced by "rich comparison" (i.e. __eq__, __le__, etc.).
Since booleans in Perl are integers, renaming __cmp__ to __eq__ is often enough while wrapping a Perl object in Python.
- perl.require, perl.use and perl.eval accept either bytes or strings.
SOURCE REPOSITORY
The Github repository for this project is at <https://github.com/niner/inline-python-pm>.
Pull requests are welcome.
AUTHOR
Neil Watkiss <NEILW@cpan.org>
Brian Ingerson <INGY@cpan.org> is the author of Inline, Inline::C and Inline::CPR. He was
responsible for much encouragement and many suggestions throughout the development of
Inline::Python.
Eric Wilhelm provided support for 'new-style' classes in version 0.21. Many thanks, Eric!
Stefan Seifert <NINE@cpan.org> fixed some bugs and is current co-maintainer.
COPYRIGHT
Copyright (c) 2001, Neil Watkiss.
All Rights Reserved. This module is free software. It may be used, redistributed and/or
modified under the same terms as Perl itself.
(see http://www.perl.com/perl/misc/Artistic.html)