extensions for linux 0.4

extensions is a simple plugin system inspired from setuptools entry points. It allows an application to define and/or use plugins.<br /><br />How to define a plugin<br /><br />A plugin can be any callable object . It has to be registered through the extensions registry.<br /><br />For example, let's take a simple function that calculates the average of some numbers, and let's save it into a file called extensions.py in a package called myapp:<br /><br />def average(*args):<br /> return sum(args) / len(args)<br /><br />This function can be registered in the plugin system using the register function. Plugins have a name and belong to a group. For our example, the group can be myapp.operator and the name average:<br /><br />from extensions import register<br /><br /># usage : register(group, name, location)<br />register('myapp.operator', 'average', 'myapp.extensions:average')<br /><br />The third parameter gives the location of the callable, with the form module_name:attrs, where module_name is the full name of the module, and attrs the attributes in the module.<br /><br />Notice that the group name includes the name of the package, which is a good practice to avoid collisions since the group names are global to all applications that use extensions.<br /><br />Using a configuration file<br /><br />There's another way to register your plugins by using a configuration file. You can write a ini-like file, using groups for sections title, and name = location for the values.<br /><br />For example, if you create a operators.cfg file with this content:<br /><br />[myapp.operator]<br /><br />average = myapp.extensions:average<br /><br />You will be able to load it using register_file:<br /><br />from extensions import register_file<br /><br />register_file('operators.cfg')<br /><br />This function will scan your file and register the plugins for you.<br /><br />How to use a plugin<br /><br />Iterate over registered plugins<br /><br />extensions provides a get function that allows you to iterate over all registered plugins for a given group:<br /><br />from extensions import get<br /><br />for plugin in get(group='myapp.operator'):<br /> print plugin.name<br /><br />You can also give the name to the function:<br /><br />for plugin in get(group='myapp.operator', name='average'):<br /> print plugin.name<br /><br />Or even iterate over all plugins:<br /><br />from itertools import islice<br /><br />for plugin in islice(get(), 5):<br /> print plugin.name<br /><br />The Plugin object<br /><br />The objects returned by the get function are Plugin class instances.<br /><br />The Plugin class provides one method called load, that returns the registered object, so you can use it<br /><br /># let's get the plugin `average` of the group `myapp.operator`<br />plugin = get(group='myapp.operator', name='average').next()<br /><br /># let's load it<br />func = plugin.load()<br /><br /># let's use it now<br />average = func(1, 2, 3)<br /><br />Plugin also provides a name and a group attribute, that corresponds to the name of the registered plugin, and to its group.<br /><br />Distribute your plugins<br /><br />If you want to distribute your plugins, you just have to import the module that registers the plugins into your setup.py file:<br /><br />from distutils.core import setup<br />from myapp import plugins # registers the plugins<br /><br />setup(name='myapp', version='1.0'<br /> packages=['myapp'])<br /><br />This will register the plugins when the package is installed by creating a special file called PLUGINS into the .egg-info directory created when your package is installed.<br /><br />Compatibility with setuptools entry points<br /><br />extensions is fully compatible with setuptools entry points. So you can iterate and use entry points defined in third-party applications that are installed in your Python.<br /><br />If you want to iterate through setuptools entry points, use the consume_entry_points option when you call the get function:<br /><br />plugins = get(consume_entry_points=True)<br /><br />This will iterate over extensions plugins and setuptools entry points.<br /><br />#md5=e498fe6da146aefb677c3e8a210fbb29

Requirements:	No special requirements
Platforms:	*nix, Linux
Keyword:	Called,  Entry,  Extensions,  Extensions Linux,  Function,  Getgroup Myappoperator,  Group,  Import,  Iterate,  Let039s,  Linux,  Package,  Plugin,  Plugins,  Points,  Print,  Register,  Registered,  Setuptools
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