def _pointsFromList(L):
    """
    given a list of coordinates [x0, y0, x1, y1....]
    produce a list of points [(x0,y0), (y1,y0),....]
    """
    P = []
    a = P.append
    for i in range(0, len(L), 2):
        a((L[i], L[i + 1]))
    return P
