A simple python plugin system using a custom metaclass

plugin.py

	# a simple Python plugin loading system
	# see http://stackoverflow.com/questions/14510286/plugin-architecture-plugin-manager-vs-inspecting-from-plugins-import

	class PluginMount(type):
	"""
	A plugin mount point derived from:
	http://martyalchin.com/2008/jan/10/simple-plugin-framework/
	Acts as a metaclass which creates anything inheriting from Plugin
	"""

	def __init__(cls, name, bases, attrs):
	"""Called when a Plugin derived class is imported"""

	if not hasattr(cls, 'plugins'):
	# Called when the metaclass is first instantiated
	cls.plugins = []
	else:
	# Called when a plugin class is imported
	cls.register_plugin(cls)

	def register_plugin(cls, plugin):
	"""Add the plugin to the plugin list and perform any registration logic"""

	# create a plugin instance and store it
	# optionally you could just store the plugin class and lazily instantiate
	instance = plugin()

	# save the plugin reference
	cls.plugins.append(instance)

	# apply plugin logic - in this case connect the plugin to blinker signals
	# this must be defined in the derived class
	instance.register_signals()


	class Plugin(object):
	"""A plugin which must provide a register_signals() method"""
	__metaclass__ = PluginMount


	class MyPlugin(Plugin):
	def register_signals(self):
	print "Class created and registering signals"

	def other_plugin_stuff(self):
	print "I can do other plugin stuff"


	for plugin in Plugin.plugins:
	plugin.other_plugin_stuff()