<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _reload(self, force=False):
 """Reloads the configuration from the file and environment variables. Useful if using `os.environ` instead of this class' `set_env` method, or if the underlying configuration file is changed externally. """

        self._config_map = dict()
        self._registered_env_keys = set()
        self.__reload_sources(force)
        self.__load_environment_keys()
        self.verify()
        self._clear_memoization()