[New-bugs-announce] [issue13264] Monkeypatching using metaclass

[Artem Tomilov]

New submission from Artem Tomilov <scraplesh at gmail.com>:

from abc import ABCMeta

class Meta(ABCMeta):
    def __instancecheck__(cls, instance):
        # monkeypatching class method
        cls.__subclasscheck__ = super(Meta, cls).__subclasscheck__
        return super(Meta, cls).__instancecheck__(instance)

    def __subclasscheck__(cls, sub):
        return cls in sub.mro()

class A(object):
    __metaclass__ = Meta

class B(object): pass

# registering class 'B' as a virtual subclass of 'A'
A.register(B)

>>> issubclass(B, A)
False
>>> isinstance(B(), A) # => method __subclasscheck__ is now monkeypatched
True
>>> issubclass(B, A) # => desire to get 'True' because 'B' is a virtual subclass
False

----------
components: None
messages: 146366
nosy: Artem.Tomilov
priority: normal
severity: normal
status: open
title: Monkeypatching using metaclass
type: behavior
versions: Python 2.7

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue13264>
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