"The purpose of callable is to report whether an instance is callable or not"

I am totally with you so far until you get to: "and that information is available on the instance's class, via the presence of __call__". I don't understand why this assumption must be made. The following class is totally valid and callable (in the sense that I can use function call syntax on instances):

class C(object):
    @property
    def __call__(self):
        return lambda: None


Also, I don't understand why you would mention __iter__, __iter__ respects the descriptor protocol also:


>>> class C(object):
...     @property
...     def __iter__(self):
...         return lambda: iter(range(10))
... 
>>> it = iter(C())
>>> next(it)
0
>>> next(it)
1
>>> next(it)
2