Return the key referring to this object

        The default value is the lower case version of the class name

        :rtype: str

def _key_name(self):  # type: () -> str
        """Return the key referring to this object

        The default value is the lower case version of the class name

        :rtype: str
        """
        if self._key is not None:
            return self._key

        return self.__class__.__name__.lower()