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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 add_done_callback(self, callback):
 """ Add a callback to run after the task completes. The callable must take 1 argument which will be the completed Task. :param callback: a callable that takes a single argument which will be the completed Task. """

        if self._done is None or self._done.is_set():
            raise ValueError('Task has already finished')
        if callable(callback):
            self.callbacks.append(callback)