@acquire<EOL><INDENT>def touch(self, conn, key, exptime):<DEDENT>
assert self._validate_key(key)<EOL>_cmd = b'<STR_LIT:U+0020>'.join([b'<STR_LIT>', key, str(exptime).encode('<STR_LIT:utf-8>')])<EOL>cmd = _cmd + b'<STR_LIT:\r\n>'<EOL>resp = yield from self._execute_simple_command(conn, cmd)<EOL>if resp not in (const.TOUCHED, const.NOT_FOUND):<EOL><INDENT>raise ClientException('<STR_LIT>', resp)<EOL><DEDENT>return resp == const.TOUCHED<EOL>
The command is used to update the expiration time of
        an existing item without fetching it.

        :param key: ``bytes``, is the key to update expiration time
        :param exptime: ``int``, is expiration time. This replaces the existing
        expiration time.
        :return: ``bool``, True in case of success.