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##############################################################################
#
# Copyright (c) 2003 Zope Corporation and Contributors.
# All Rights Reserved.
#
# This software is subject to the provisions of the Zope Public License,
# Version 2.1 (ZPL). A copy of the ZPL should accompany this distribution.
# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
# FOR A PARTICULAR PURPOSE.
#
##############################################################################
"""ExtensionClass
Extension Class exists to support types derived from the old ExtensionType
meta-class that preceeded Python 2.2 and new-style classes.
As a meta-class, ExtensionClass provides the following features:
- Support for a class initialiser:
>>> from ExtensionClass import ExtensionClass, Base
>>> class C(Base):
... def __class_init__(self):
... print 'class init called'
... print self.__name__
... def bar(self):
... return 'bar called'
class init called
C
>>> c = C()
>>> int(c.__class__ is C)
1
>>> int(c.__class__ is type(c))
1
- Making sure that every instance of the meta-class has Base as a base class:
>>> class X:
... __metaclass__ = ExtensionClass
>>> Base in X.__mro__
1
- Provide an inheritedAttribute method for looking up attributes in
base classes:
>>> class C2(C):
... def bar(*a):
... return C2.inheritedAttribute('bar')(*a), 42
class init called
C2
>>> o = C2()
>>> o.bar()
('bar called', 42)
This is for compatability with old code. New code should use super
instead.
The base class, Base, exists mainly to support the __of__ protocol.
The __of__ protocol is similar to __get__ except that __of__ is called
when an implementor is retrieved from an instance as well as from a
class:
>>> class O(Base):
... def __of__(*a):
... return a
>>> o1 = O()
>>> o2 = O()
>>> C.o1 = o1
>>> c.o2 = o2
>>> c.o1 == (o1, c)
1
>>> C.o1 == o1
1
>>> int(c.o2 == (o2, c))
1
We accomplish this by making a class that implements __of__ a
descriptor and treating all descriptor ExtensionClasses this way. That
is, if an extension class is a descriptor, it's __get__ method will be
called even when it is retrieved from an instance.
>>> class O(Base):
... def __get__(*a):
... return a
...
>>> o1 = O()
>>> o2 = O()
>>> C.o1 = o1
>>> c.o2 = o2
>>> int(c.o1 == (o1, c, type(c)))
1
>>> int(C.o1 == (o1, None, type(c)))
1
>>> int(c.o2 == (o2, c, type(c)))
1
$Id: __init__.py 40218 2005-11-18 14:39:19Z andreasjung $
"""
from _ExtensionClass import *
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