def get_box(pts):
    """Returns tight fitting bounding box (axis aligned) around set of points
    """
    assert len(pts)
    it = iter(pts)
    ll = list(next(it))
    ur = list(ll[:])
    for pt in it:
        if pt[0] < ll[0]:
            ll[0] = pt[0]
        if pt[1] < ll[1]:
            ll[1] = pt[1]
        if pt[0] > ur[0]:
            ur[0] = pt[0]
        if pt[1] > ur[1]:
            ur[1] = pt[1]
    return tuple(ll), tuple(ur)