class Vec2D(tuple):
  """A 2 dimensional vector class, used as a helper class
  for implementing turtle graphics.
  ....
  """
  def __new__(cls, x, y):
      return tuple.__new__(cls, (x, y))
  def __add__(self, other):
      return Vec2D(self[0]+other[0], self[1]+other[1])
  def __mul__(self, other):
      if isinstance(other, Vec2D):
          return self[0]*other[0]+self[1]*other[1]
      return Vec2D(self[0]*other, self[1]*other)
  def __rmul__(self, other):
      if isinstance(other, int) or isinstance(other, float):
          return Vec2D(self[0]*other, self[1]*other)

v = Vec2D(0.1, 0.0)

a = 10 * v
b = 10.0 * v
c = v * 10

print "a:", a
print "b:", b
print "c:", c