Convenience shift+rotate combination.

def pt_relative(pt=(0.0, 0.0), shift=[0.0, 0.0], angle=[0.0]):
    '''Convenience shift+rotate combination.
    '''
    assert isinstance(pt, tuple)
    l_pt = len(pt)
    assert l_pt > 1
    for i in pt:
        assert isinstance(i, float)
    assert isinstance(shift, list)
    l_sh = len(shift)
    assert l_sh == l_pt
    for i in shift:
        assert isinstance(i, float)
    assert isinstance(angle, list)
    l_angle = len(angle)
    assert l_angle == l_pt-1
    for i in angle:
        assert isinstance(i, float)
        assert abs(i) <= 2*pi

    return pt_rotate(pt_shift(pt, shift), angle, pt)