__floordiv__ in module fraction fails with TypeError instead of returning NotImplemented when modulo is a class without __rtruediv__ or __mul__.

Code sample:

class Foo(object):
    def __rdivmod__(self, other):
        return 'rdivmod works'

from fractions import Fraction
a = Fraction(1,1)
b = Foo()
print(divmod(1, b))
print(divmod(a, b))



__divmod__ in Fraction is inherited from class Real (numbers.py):
    def __divmod__(self, other):
        return (self // other, self % other)

So __floordiv__ and __mod__ are called. 

    def __floordiv__(a, b):
        """a // b"""
        return math.floor(a / b)

    def __mod__(a, b):
        """a % b"""
        div = a // b
        return a - b * div

__floordiv__ if fractions.py makes a true division, and __mod__ makes multiplication.



The following code will fix the problem:


    def __divmod__(self, other):
        if isinstance(a, numbers.Complex):
            return (self // other, self % other)
        else:
            return NotImplemented