Raymond Hettinger <raymond.hettin...@gmail.com> added the comment:
Here's an example in PEP 3119 that appears to work but actually bypasses the
method:
from abc import ABCMeta, abstractmethod
class Sized(metaclass=ABCMeta):
@abstractmethod
def __hash__(self):
return 0
@classmethod
def __instancecheck__(cls, x):
print('Called')
return hasattr(x, "__len__")
@classmethod
def __subclasscheck__(cls, C):
return hasattr(C, "__bases__") and hasattr(C, "__len__")
$ python3.10 -i demo_3119.py
>>> isinstance([], Sized)
True
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<https://bugs.python.org/issue45791>
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