def _lookup_required_session(self, key):
session = self.session_handler.do_get_session(key)<EOL>if (not session):<EOL><INDENT>msg = ("<STR_LIT>"<EOL>"<STR_LIT>" + str(key) + "<STR_LIT>")<EOL>raise ValueError(msg)<EOL><DEDENT>return session<EOL>
:returns: SimpleSession