docs: def unwrap_err(self) -> E:
          """
          Returns the error value in a :class:`Result`.
  
          Returns:
              The error value in the :class:`Result` if it is a
              :meth:`Result.Err` value.
  
          Raises:
              ``ValueError`` with the message provided by the success value
               if the :class:`Result` is a :meth:`Result.Ok` value.
  
          Examples:
              >>> try:
              ...     Ok(1).unwrap_err()
              ... except ValueError as e:
              ...     print(e)
              1
              >>> Err('Oh No').unwrap_err()
              'Oh No'
          """
          if self._is_ok:
              raise ValueError(self._val)
          return cast(E, self._val)