def intersection(l1, l2):
    """
    Compute intersect point of two lines l1 and l2
    l1: line
    l2: line
    return: Intersect Point
    """
    x1, y1, x2, y2 = l1.point
    x3, y3, x4, y4 = l2.point
    a1, b1 = y2 - y1, x1 - x2
    c1 = a1 * x1 + b1 * y1
    a2, b2 = y4 - y3, x3 - x4
    c2 = a2 * x3 + b2 * y3
    det = a1 * b2 - a2 * b1
    assert det, "lines are parallel"
    return (1. * (b2 * c1 - b1 * c2) / det, 1. * (a1 * c2 - a2 * c1) / det)