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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 undo(self):
 """ Raises IndexError if more than one group is open, otherwise closes it and invokes undo_nested_group. """

        if self.grouping_level() == 1:
            self.end_grouping()
        if self._open:
            raise IndexError
        self.undo_nested_group()
        self.notify()