You also need to implement __rmul__. When the initial call to int.__mul__(7, v) fails, Python will next try type(v).__rmul__(v, 7).
def __rmul__(self, lhs):
return self * lhs # Effectively, turn 7 * v into v * 7
As Rawing points out, you could simply write __rmul__ = __mul__ for this definition. __rmul__ exists to allow for non-commutative multiplication where simply deferring to __mul__ with the operands reversed isn't sufficient.
For instance, if you were writing a Matrix class and wanted to support multiplication by a nested list, e.g.,
m = Matrix(...) # Some 2 x 2 matrix
n = [[1, 2], [3,4]]
p = n * m
Here, the list class wouldn't know how to multiple a list by a Matrix instance, so when list.__mul__(n, m) fails, Python would next try Matrix.__rmul__(m, n). However, n * m and m * n are two different results in general, so Matrix.__rmul__(m, n) != Matrix.__mul__(m, n); __rmul__ has to do a little extra work to generate the right answer.
