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 deserialize(self, value):
        value = decode(value).strip()
        expanded = path.expand_path(value)
        validators.validate_required(value, self._required)
        validators.validate_required(expanded, self._required)
        if not value or expanded is None:
            return None
        return _ExpandedPath(value, expanded)