Returns the cross product of two Vectors

def cross(vec1, vec2):
        """Returns the cross product of two Vectors"""
        if isinstance(vec1, Vector3) and isinstance(vec2, Vector3):
            vec3 = Vector3()
            vec3.x = (vec1.y * vec2.z) - (vec1.z * vec2.y)
            vec3.y = (vec1.z * vec2.x) - (vec1.x * vec2.z)
            vec3.z = (vec1.x * vec2.y) - (vec1.y * vec2.x)
            return vec3
        else:
            raise TypeError("vec1 and vec2 must be Vector3's")