def __missing__(self, key):
        if self.default_factory is None:
            raise KeyError(key)
        else:
            ret = self[key] = self.default_factory(name=key)
            return ret
def __enter__(self):
        entering = not transaction_states[self.using]
        transaction_states[self.using].begin()
        self._no_monkey.__enter__(self)
        if entering:
            on_commit(transaction_states[self.using].commit, self.using)