1# Copyright 2013 The Distro Tracker Developers 

2# See the COPYRIGHT file at the top-level directory of this distribution and 

3# at https://deb.li/DTAuthors 


5# This file is part of Distro Tracker. It is subject to the license terms 

6# in the LICENSE file found in the top-level directory of this 

7# distribution and at https://deb.li/DTLicense. No part of Distro Tracker, 

8# including this file, may be copied, modified, propagated, or distributed 

9# except according to the terms contained in the LICENSE file. 

10"""Classes to build a plugin mechanism.""" 



13class PluginRegistry(type): 

14 """ 

15 A metaclass which any class that wants to behave as a registry can use. 


17 When classes derived from classes which use this metaclass are 

18 instantiated, they are added to the list :attr:`plugins`. 

19 The concrete classes using this metaclass are free to decide how to use 

20 this list. 


22 This metaclass also adds an :meth:`unregister_plugin` classmethod to all 

23 concrete classes which removes the class from the list of plugins. 

24 """ 

25 def __init__(cls, name, bases, attrs): # noqa 

26 if not hasattr(cls, 'plugins'): 

27 cls.plugins = [] 

28 else: 

29 cls.plugins.append(cls) 


31 cls.unregister_plugin = classmethod( 

32 lambda cls: cls.plugins.remove(cls) 

33 )