segments and intersect

line_segment_intersect.py

def line_segment_intersection(p1, p2, p3, p4):
    d = (p2[0] - p1[0]) * (p4[1] - p3[1]) - (p2[1] - p1[1]) * (p4[0] - p3[0])
    if d == 0.0:
        return None

    intersect = [0.0, 0.0]
    u = ((p3[0] - p1[0]) * (p4[1] - p3[1]) - (p3[1] - p1[1]) * (p4[0] - p3[0])) / d
    v = ((p3[0] - p1[0]) * (p2[1] - p1[1]) - (p3[1] - p1[1]) * (p2[0] - p1[0])) / d
    if u < 0.0 or u > 1.0 or v < 0.0 or v > 1.0:
        return None

    px = p1[0] + u * (p2[0] - p1[0])
    py = p1[1] + u * (p2[1] - p1[1])
    if px == p1[0] and py == p1[1] or \
       px == p2[0] and py == p2[1] or \
       px == p3[0] and py == p3[1] or \
       px == p4[0] and py == p4[1]:
       return None

    return (px, py)