<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _get_database(self, database_name):
 """ Get PyMongo client pointing to the current database. :return: MongoDB client of the current database. :raise DataSourceError """

        try:
            return self._client[database_name]
        except InvalidName as ex:
            raise DataSourceError("Cannot connect to database %s!"
                                  % self._database) from ex