The callable() function doesn't respect when __call__ is a descriptor.

gistfile1.txt

class Wrapper(object):

    def __init__(self, wrapped):
        self.__wrapped__ = wrapped

    @property
    def __call__(self):
        return self.__wrapped__.__call__

>>> wrapper = Wrapper(None)

>>> hasattr(wrapper, '__call__')
False

>>> getattr(wrapper, '__call__')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "callable.py", line 8, in __call__
    return self.__wrapped__.__call__
AttributeError: 'NoneType' object has no attribute '__call__'

>>> wrapper.__call__
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "callable.py", line 8, in __call__
    return self.__wrapped__.__call__
AttributeError: 'NoneType' object has no attribute '__call__'

>>> wrapper()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "callable.py", line 8, in __call__
    return self.__wrapped__.__call__
AttributeError: 'NoneType' object has no attribute '__call__'

>>> callable(wrapper)
True