Python 2.6 / 3.0: Determining if a method is inherited

[Pekka Laukkanen]

2008/10/5 Fuzzyman <fuzzyman at gmail.com>:
> I may well be being dumb (it has happened before), but I'm struggling
> to fix some code breakage with Python 2.6.
>
> I have some code that looks for the '__lt__' method on a class:
>
> if hasattr(clr, '__lt__'):
>
> However - in Python 2.6 object has grown a default implementation of
> '__lt__', so this test always returns True.
>
>>>> class X(object): pass
> ...
>>>> X.__lt__
> <method-wrapper '__lt__' of type object at 0xa15cf0>
>>>> X.__lt__ == object.__lt__
> False
>
> So how do I tell if the X.__lt__ is inherited from object? I can look
> in the '__dict__' of the class - but that doesn't tell me if X
> inherits '__lt__' from a base class other than object. (Looking inside
> the method wrapper repr with a regex is not an acceptable answer...)

I don't have Python 2.6 available, but if __lt__ on it works similarly
as __str__ on Python 2.5, you might be able to achieve this either
with inspect.ismethod or by checking methods' im_class attribute
directly:

>>> class C(object):
...     pass
...
>>> class D(object):
...     def __str__(self):
...         return ''
...
>>> class E(D):
...     pass
...
>>> import inspect
>>> inspect.ismethod(C().__str__)
False
>>> inspect.ismethod(D().__str__)
True
>>> inspect.ismethod(E().__str__)
True
>>>
>>> C().__str__.im_class
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'method-wrapper' object has no attribute 'im_class'
>>> D().__str__.im_class
<class '__main__.D'>
>>> E().__str__.im_class
<class '__main__.E'>


Cheers,
    .peke