def direction_correct(points, i1, i2, i3):
p1, p2, p3 = points[i1], points[i2], points[i3]
d = Point.direction(p1, p2, p3)
return (d > 0 or d == 0 and p1.dist_to_point(p2) > p1.dist_to_point(p3))
def left_points(points, p1, p2):
'''Points at the left of vector p1->p2 and p1, p2'''
return ([p1] +
list(filter(lambda p: Point.direction(p1, p2, p) < 0, points)) +
[p2])