• Distutils
• PluginSystem

example

        class MyCmd(sdist):

            # this is a regular user option
            manifest_makers = ['svn', 'template', 'hg']

            # this manages all extensions
            extensions = Extensible('manifest_makers')

            def run(self):
                # this will build the filelist by running the plugins
                self.extensions.run('manifest_makers')


        dist = Distribution()
        cmd = MyCmd(dist)
        cmd.ensure_finalized()
        cmd.run()

Notice that self.extensions.load(self) is implicitely called by Command.

code

"""Extendable command"""
import os
import pkg_resources

class Extensible(object):

    def __init__(self, *options):
        self.options = options
        self._ext = {}

    def load(self, cmd):
        for opt in self.options:
            ep = ExtensionPoint(cmd, opt)
            ep.load()
            self._ext[opt] = ep

    def run(self, name):
        self._ext[name].run()

class ExtensionPoint(object):

    def __init__(self, cmd, name):
        self.name = name
        self.cmd = cmd
        self.entries = []

    def load(self, name=None):
        if name is None:
            name = self.cmd.get_command_name()
            entry_point = 'distutils.%s:%s' % (name, self.name)
        else:
            entry_point = name
        self._entries = [entry for entry in [self._load(ep) for ep in
                         pkg_resources.iter_entry_points(entry_point)]
                         if entry is not None]

    def _load(self, entry_point):
        values = getattr(self.cmd, self.name)
        if not isinstance((list, tuple), values):
            values = [values]
        entry_point = entry_point.load()
        if entry_point.name not in values:
            return None
        return entry_point

    def run(self):
        for ep in self._entries:
            entry_point(self.cmd, self.name)

    def apply(self, name=None):
        self.load(name)
        self.run()