@classmethod
def get_backend(cls):
    """
        Return name of currently active backend.
        if no backend has been loaded, loads and returns name of default backend.

        :raises passlib.exc.MissingBackendError:
            if no backends are available.

        :returns:
            name of active backend
        """
    if not cls.__backend:
        cls.set_backend()
        assert cls.__backend, 'set_backend() failed to load a default backend'
    return cls.__backend
