scalar production of vec2d gives error about cymunk HOT 1 CLOSED

The reason of this behavior is that the Vec2d class uses pythons magic function (__mul__...) format but cython magic functions behave differently.
See http://cython.readthedocs.io/en/latest/src/userguide/special_methods.html#arithmetic-methods.

There are no "right side of operation" functions (rmul, rsub,...) like in python. but the same arithmetic function is called for the right side with self set to the left value and other to the right if the magic function of the left side returns NotImplemented

A fix for the __mul__ function could look like this:

    def __mul__(self, other):
        if not isinstance(self, Vec2d):
            self, other = other, self
        if isinstance(other, Vec2d):
            return Vec2d(self.x * other.x, self.y * other.y)
        if (hasattr(other, "__getitem__")):
            return Vec2d(self.x*other[0], self.y*other[1])
        else:
            return Vec2d(self.x*other, self.y*other)

I could prepare a PR with "cythonized" magic functions some when the next days.

from cymunk.