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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 restore_walker(self, dumped_state):
 """Restore a stream walker that was previously serialized. Since stream walkers need to be tracked in an internal list for notification purposes, we need to be careful with how we restore them to make sure they remain part of the right list. Args: dumped_state (dict):
 The dumped state of a stream walker from a previous call to StreamWalker.dump() Returns: StreamWalker: The correctly restored StreamWalker subclass. """


        selector_string = dumped_state.get(u'selector')
        if selector_string is None:
            raise ArgumentError("Invalid stream walker state in restore_walker, missing 'selector' key", state=dumped_state)

        selector = DataStreamSelector.FromString(selector_string)

        walker = self.create_walker(selector)
        walker.restore(dumped_state)
        return walker