def is_set(self, key: Union[str, ConfigVar, ConfigVarWithConfig]) -> bool:
        """Returns whether the config key has any explicit value set/defined."""
        if isinstance(key, (ConfigVar, ConfigVarWithConfig)):
            key = key.key()
        assert isinstance(key, str), key
        return self.get(key, default=...) is not ...
Returns whether the config key has any explicit value set/defined.
electrum/simple_config.py