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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 _model_class_from_pk(definition_cls, definition_pk):
 """ Helper used to unpickle MutableModel model class from their definition pk. """

    try:
        return definition_cls.objects.get(pk=definition_pk).model_class()
    except definition_cls.DoesNotExist:
        pass