def METHOD_NAME(self, backup):
    """
    Restore a previous state saved with repr()
    This function allows you to "snapshot" the current values of
    the configuration and reload them later on. Any missing
    default values will be added on top of the restored config.
    Returns True if new keys from the default config have been added,
    False if no keys have been added (backup contains all default keys)
    >>> c = JsonConfig()
    >>> c.a.b = 10
    >>> backup = repr(c)
    >>> print(c.a.b)
    10
    >>> c.a.b = 11
    >>> print(c.a.b)
    11
    >>> c._restore(backup)
    False
    >>> print(c.a.b)
    10
    """
    self._data = json.loads(backup)
    # Add newly-added default configuration options
    if self._default is not None:
        return self._merge_keys(self._default)
    return False