lars van gemerden wrote:
> Hi all,
>
> i was writing a function to determine the common base class of a number
> classes:
>
> def common_base(classes):
> if not len(classes):
> return None
> common = set(classes.pop().mro())
> for cls in classes:
> common.intersection_update(cls.mro())
> while len(common) > 1:
> cls1 = common.pop()
> cls2 = common.pop()
> if issubclass(cls1, cls2):
> common.add(cls1)
> elif issubclass(cls2, cls1):
> common.add(cls2)
> return common.pop()
>
> and ran common_base(int, float), hoping to get numbers.Number.
>
> this did not work because abstract base classes are not always in the
> mro() of classes.
>
> My question is: is there a way to obtain the abc's of a class or otherwise
> a way to make the function above take abc's into account (maybe via a
> predefined function)?
The abstract base classes may run arbitrary code to determine the subclass
relationship:
>>> from abc import ABCMeta
>>> import random
>>> class Maybe(metaclass=ABCMeta):
... @classmethod
... def __subclasshook__(cls, C):
... print("processing", C)
... return random.choice((False, True))
...
>>> isinstance(1.1, Maybe)
processing <class 'float'>
True
>>> isinstance(1.1, Maybe)
True
>>> isinstance(1, Maybe)
processing <class 'int'>
False
>>> issubclass(float, Maybe)
True
You'd have to check every pair of classes explicitly and might still miss
(for example) numbers.Number as the module may not have been imported.
I think you are out of luck.
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