rotate points

rotate.py

import math

def rotate_vector(v, angle, anchor):
    """Rotate a vector `v` by the given angle, relative to the anchor point."""
    x, y = v

    x = x - anchor[0]
    y = y - anchor[1]
    # Here is a compiler optimization; inplace operators are slower than
    # non-inplace operators like above. This function gets used a lot, so
    # performance is critical.

    cos_theta = math.cos(math.radians(angle))
    sin_theta = math.sin(math.radians(angle))

    nx = x*cos_theta - y*sin_theta
    ny = x*sin_theta + y*cos_theta

    nx = nx + anchor[0]
    ny = ny + anchor[1]
    return [nx, ny]

print rotate_vector((1,0),45,(0,0))