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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 follow_model(self, model):
 """ Follow a particular model class, updating associated Activity objects automatically. """

        if model:
          self.models_by_name[model.__name__.lower()] = model
          signals.post_save.connect(create_or_update, sender=model)
          signals.post_delete.connect(self.remove_orphans, sender=model)