User defined __mul__ method is not commutative

Question

I wrote a class to represent vectors in Python (as an exercise) and I\'m having problems with extending the built-in operators.

I defined a __mul__ meth

Answer 1

If you want commutativity for different types you need to implement __rmul__(). If implemented, it is called, like all __r*__() special methods, if the operation would otherwise raise a TypeError. Beware that the arguments are swapped:

class Foo(object):
    def __mul_(self, other):
        ''' multiply self with other, e.g. Foo() * 7 '''
    def __rmul__(self, other):
        ''' multiply other with self, e.g. 7 * Foo() '''

Answer 2

I believe you are looking for __rmul__