def test_postPathToPrePath(self):
        """
        As path segments from the request are traversed, they are taken from
        C{postpath} and put into C{prepath}.
        """
        request = DummyRequest([b"foo", b"bar"])
        root = Resource()
        child = Resource()
        child.isLeaf = True
        root.putChild(b"foo", child)
        self.assertIdentical(child, getChildForRequest(root, request))
        self.assertEqual(request.prepath, [b"foo"])
        self.assertEqual(request.postpath, [b"bar"])

        As path segments from the request are traversed, they are taken from
        C{postpath} and put into C{prepath}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_resource.py