docs: def is_strict_subclass (value, klass):
      """Check that `value` is a subclass of `klass` but that it is not actually
      `klass`. Unlike issubclass(), does not raise an exception if `value` is
      not a type.
  
      """
      return (isinstance (value, type) and
              issubclass (value, klass) and
              value is not klass)