def METHOD_NAME(self, key, value):
    """Change the state of the instance data with the given \
    ``key`` and the provided ``value``.
    Wrapping with a decorator is probably not necessary.
    :param key: A ``str`` containing the key to update
    :param value: A value to change the ``key`` to
    :return: None
    """
    if key not in VALID_KEYS:
        raise InvalidState
    self._data[key] = value