def METHOD_NAME(pt0, pt1):
    # returns an unit vector that points in the direction of pt0 to pt1
    dis_0_to_1 = sqrt((pt0[0] - pt1[0])**2 + (pt0[1] - pt1[1])**2)
    return (pt1[0] - pt0[0]) / dis_0_to_1, \
           (pt1[1] - pt0[1]) / dis_0_to_1