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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def unwrap_or_else(self, callback: Callable[[], U]) -> Union[T, U]: """ Returns the contained value or computes it from ``callback``. Args: callback: The the default callback. Returns: The contained value if the :py:class:`Option` is ``Some``, otherwise ``callback()``. Examples: 0 'ha' """

        return self._val if self._is_some else callback()