def test_append(self):
        """
        L{MemCacheProtocol.append} behaves like a L{MemCacheProtocol.set}
        method: it returns a L{Deferred} which is called back with C{True} when
        the operation succeeds.
        """
        return self._test(
            self.proto.append(b"foo", b"bar"),
            b"append foo 0 0 3\r\nbar\r\n", b"STORED\r\n", True)

        L{MemCacheProtocol.append} behaves like a L{MemCacheProtocol.set}
        method: it returns a L{Deferred} which is called back with C{True} when
        the operation succeeds.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_memcache.py