Provided by: python-straight.plugin-doc_1.4.1-3_all 
NAME
straightplugin - straight.plugin Documentation
GETTING STARTED
Install
pip install straight.plugin
That was super easy.
Decide on a Namespace
You’ll want to decide on a namespace within your package where you’ll keep your own
plugins and where other developers can add more plugins for your package to use.
For example, if you’re writing a log filtering library named logfilter you may choose
logfilter.plugins as a package to hold your plugins, so you’ll create the empty package as
you would any other python package. However, the only contents of
logfilter/plugins/__init__.py will be a little bit of special code telling python this is
a namespace package.
# This file will not be needed in Python 3.3
from pkgutil import extend_path
__path__ = extend_path(__path__, __name__)
Now, any modules you place in this package are plugin modules able to be loaded by
straight.plugin.
from straight.plugin import load
plugins = load("logfilter.plugins")
If you’ll be using more plugins than writing them, you should read more about the loaders
available and how they work.
Write a Plugin
Writing a plugin is even easier than loading them. There are two important plugin types to
learn: Module plugins and class Plugins. Every module in your namespace package is a
module plugin. Every class they define is a class plugin.
When you load module plugins, you get all of them.
When you load class plugins, you filter them by a common base and only get those class
plugins which inherit it.
Module plugins are simple and usually define a few functions with names expected by
whoever is loading and using the plugins.
# This is a module plugin
def add_extra(data):
if 'x' in data and 'y' in data:
data['z'] = x * y
# This was a fairly useless plugin
Class plugins are only a little longer, but can be a bit more controlled to work with.
They depend on a common class the plugins inherit, and this would be defined by the
project loading and using the plugins.
# This is a class plugin
class RstContentParser(ContentPlugin):
"""Parses any .rst files in a bundle."""
extensions = ('.rst',)
def parse(self, content_file):
src = content_file.read()
return self.parse_string(src)
def parse_string(self, src):
parts = publish_parts(source=src, writer_name='html')
return parts['html_body']
You can fit as many class plugins inside a module plugin as you want, and to load them
instead of the modules you simply pass a subclasses parameter to load().
from straight.plugin import load
plugins = load("jules.plugins", subclasses=ContentPlugin)
The resulting set of plugins are all the classes found which inherit from ContentPlugin.
You can do whatever you want with these, but there are some helpful tools to make it
easier to work with Class plugins.
You can easily create instances of all the classes, which gives you a set of Instance
plugins.
instances = plugins.produce()
You can even pass initialization parameters to produce() and they’ll be used when creating
instances of all the classes. You can see the API docs for the PluginManager to see the
other ways you can work with groups of plugins.
WRITING PLUGINS
Plugins can exist inside your existing packages or in special namespace packages, which
exist only to house plugins.
The only requirement is that any package containing plugins be designated a “namespace
package”, which is currently performed in Python via the pkgutil.extend_path utility, seen
below. This allows the namespace to be provided in multiple places on the python
sys.path, where import looks, and all the contents will be combined.
Use a namespace package
This allows multiple packages installed on your system to share this name, so they may
come from different installed projects and all combine to provide a larger set of plugins.
Example
# logfilter/__init__.py
from pkgutil import extend_path
__path__ = extend_path(__path__, __name__)
# logfilter/hide_extra.py
from logfilter import Skip
def filter(log_entry):
level = log_entry.split(':', 1)[0]
if level != 'EXTRA':
return log_entry
else:
raise Skip()
Using the plugin
In our log tool, we might load all the modules in the logfilter namespace, and then use
them all to process each entry in our logs. We don’t need to know all the filters ahead
of time, and other packages can be installed on a user’s system providing additional
modules in the namespace, which we never even knew about.
from straight.plugin import load
class Skip(Exception):
pass
plugins = load('logfilter')
def filter_entry(log_entry):
for plugin in plugins:
try:
log_entry = plugin.filter(log_entry)
except Skip:
pass
return log_entry
Distributing Plugins
If you are writing plugins inside your own project to use, they’ll be distributed like any
other modules in your package. There is no extra work to do here.
However, if you want to release and distribute plugins on their own, you’ll need to tell
your setup.py about your namespace package.
setup(
# ...
namespace_packages = ['logfilter.plugins']
)
This will make sure when your plugins are installed alongside the original project, both
are importable, even though they came from their own distributions.
You can read more about this at the Distribute documentation on namespace packages.
PLUGIN LOADERS
Currently, three simple loaders are provided.
• The ModuleLoader simply loads the modules found
• The ClassLoader loads the subclasses of a given type
• The ObjectLoader loads arbitrary objects from the modules
ClassLoader
The recommended loader is the ClassLoader, used to load all the classes from all of the
modules in the namespace given. Optionally, you can pass a subclasses parameter to load(),
which will filter the loaded classes to those which are a sub-class of any given type.
For example,
import os
from straight.plugin.loaders import ClassLoader
from myapp import FileHandler
plugins = ClassLoader().load('myplugins', subclasses=FileHandler)
for filename in os.listdir('.'):
for handler_cls in plugins:
handler = handler_cls(filename)
if handler.valid():
handler.process()
However, it is preferred that you use the load() helper provided.
from straight.plugin import load
plugins = load('myplugins', subclasses=FileHandler)
This will automatically use the ClassLoader when given a subclasses argument.
ModuleLoader
Before anything else, straight.plugin loads modules. The ModuleLoader is used to do this.
from straight.plugin.loaders import ModuleLoader
plugins = ModuleLoader().load('myplugins')
A note about PEP-420:
Python 3.3 will support a new type of package, the Namespace Package. This allows
language-level support for the namespaces that make straight.plugin work and when 3.3
lands, you can create addition plugins to be found in a namespace. For now, continue to
use the pkgutil boilerplate, but when 3.3 is released, straight.plugin already supports
both forms of namespace package!
ObjectLoader
If you need to combine multiple plugins inside each module, you can load all the objects
from the modules, rather than the modules themselves.
from straight.plugin.loaders import ObjectLoader
plugins = ObjectLoader().load('myplugins')
STRAIGHT PLUGIN API
Loaders
straight.plugin.loaders.unified_load(namespace, subclasses=None, recurse=False)
Provides a unified interface to both the module and class loaders, finding modules
by default or classes if given a subclasses parameter.
class straight.plugin.loaders.Loader(*args, **kwargs)
Base loader class. Only used as a base-class for other loaders.
class straight.plugin.loaders.ModuleLoader(recurse=False)
Performs the work of locating and loading straight plugins.
This looks for plugins in every location in the import path.
class straight.plugin.loaders.ObjectLoader(recurse=False)
Loads classes or objects out of modules in a namespace, based on a provided
criteria.
The load() method returns all objects exported by the module.
class straight.plugin.loaders.ClassLoader(recurse=False)
Loads classes out of plugin modules which are subclasses of a single given base
class.
PluginManager
class straight.plugin.manager.PluginManager(plugins)
call(methodname, *args, **kwargs)
Call a common method on all the plugins, if it exists.
first(methodname, *args, **kwargs)
Call a common method on all the plugins, if it exists. Return the first
result (the first non-None)
pipe(methodname, first_arg, *args, **kwargs)
Call a common method on all the plugins, if it exists. The return value of
each call becomes the replaces the first argument in the given argument list
to pass to the next.
Useful to utilize plugins as sets of filters.
produce(*args, **kwargs)
Produce a new set of plugins, treating the current set as plugin factories.
GLOSSARY
distribution
Separately installable sets of Python modules as stored in the Python package
index, and installed by distutils or setuptools.
definition taken from PEP 382 text
module An importable python namespace defined in a single file.
namespace package
Mechanism for splitting a single Python package across multiple directories on
disk. One or more distributions (see distribution) may provide modules which exist
inside the same namespace package.
definition taken from PEP 382 text
package
A Python package is a module defined by a directory, containing a __init__.py file,
and can contain other modules or other packages within it.
package/
__init__.py
subpackage/
__init__.py
submodule.py
see also, namespace package
vendor package
Groups of files installed by an operating system’s packaging mechanism (e.g. Debian
or Redhat packages install on Linux systems).
definition taken from PEP 382 text
Straight Plugin is very easy.
Straight Plugin provides a type of plugin you can create from almost any existing Python
modules, and an easy way for outside developers to add functionality and customization to
your projects with their own plugins.
Using any available plugins is a snap.
from straight.plugin import load
plugins = load('theproject.plugins', subclasses=FileHandler)
handlers = plugins.produce()
for line in open(filename):
print handlers.pipe(line)
And, writing plugins is just as easy.
from theproject import FileHandler
class LineNumbers(FileHandler):
def __init__(self):
self.lineno = 0
def pipe(line):
self.lineno += 1
return "%04d %s" % (self.lineno, line)
Plugins are found from a namespace, which means the above example would find any
FileHandler classes defined in modules you might import as theproject.plugins.default or
theproject.plugins.extra. Through the magic of namespace packages, we can even split these
up into separate installations, even managed by different teams. This means you can ship
a project with a set of default plugins implementing its behavior, and allow other
projects to hook in new functionality simply by shipping their own plugins under the same
namespace.
Get started and learn more, today
MORE RESOURCES
• Full Documentation: http://readthedocs.org/docs/straightplugin/
• Mailing List: https://groups.google.com/forum/#!forum/straight.plugin
• genindex
• modindex
• search
AUTHOR
Calvin Spealman
COPYRIGHT
2019, Calvin Spealman