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 __exit__(self, exc_type, exc_val, exc_tb):
        connection = connections[get_tenant_database_alias()]

        connection.set_tenant(self._previous_tenant.pop())