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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 choice_default_invalidator(self, obj):
 """Invalidated cached items when the Choice changes."""

        invalid = [('Question', obj.question_id, True)]
        for pk in obj.voters.values_list('pk', flat=True):
            invalid.append(('User', pk, False))
        return invalid