$ pip install simple_plugins

>>> from simple_plugins import PluginMount

>>> class BaseHttpResponse(object):
...     """Mount point is not registered as a plugin"""
...
...     status_code = None
...
...     __metaclass__ = PluginMount
...
...     class Meta:
...         id_field = 'status_code'
...
...     def __repr__(self):
...         return "<%s: %s>" % (self.__class__.__name__, self.status_code)
...

>>> class OK(BaseHttpResponse):
...     status_code = 200
...

>>> class BaseRedirection(BaseHttpResponse):
...     """'Base*' classes are not registered as plugins"""
...     pass
...

>>> class MovedPermanently(BaseRedirection):
...     status_code = 301
...

>>> class NotModified(BaseRedirection):
...     status_code = 304
...

>>> class BadRequest(BaseHttpResponse):
...     status_code = 400
...

>>> class NotFound(BaseHttpResponse):
...     status_code = 404
...

# All plugin info
>>> BaseHttpResponse.plugins.keys()
['valid_ids', 'instances_sorted_by_id', 'id_to_class', 'instances',
 'classes', 'class_to_id', 'id_to_instance']

# Plugin info can be accessed using either dict...
>>> BaseHttpResponse.plugins['valid_ids']
set([304, 400, 404, 200, 301])

# ... or object notation
>>> BaseHttpResponse.plugins.valid_ids
set([304, 400, 404, 200, 301])

>>> BaseHttpResponse.plugins.classes
set([<class '__main__.NotFound'>, <class '__main__.OK'>,
     <class '__main__.NotModified'>, <class '__main__.BadRequest'>,
     <class '__main__.MovedPermanently'>])

>>> BaseHttpResponse.plugins.id_to_class[200]
<class '__main__.OK'>

>>> BaseHttpResponse.plugins.id_to_instance[200]
<OK: 200>

>>> BaseHttpResponse.plugins.instances_sorted_by_id
[<OK: 200>, <MovedPermanently: 301>, <NotModified: 304>, <BadRequest: 400>, <NotFound: 404>]

# Unregister the `NotFound` plugin
>>> NotFound._unregister_plugin()
>>> BaseHttpResponse.plugins.instances_sorted_by_id
[<OK: 200>, <MovedPermanently: 301>, <NotModified: 304>, <BadRequest: 400>]

# Coerce the passed value into the right instance
>>> BaseHttpResponse.coerce(200)
<OK: 200>