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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 update_count(self):
 """ updates rating count and rating average """

        node_rating_count = self.node.rating_count
        node_rating_count.rating_count = self.node.rating_set.count()
        node_rating_count.rating_avg = self.node.rating_set.aggregate(rate=Avg('value'))['rate']

        # if all ratings are deleted the value will be None!
        if node_rating_count.rating_avg is None:
            # set to 0 otherwise we'll get an exception
            node_rating_count.rating_avg = 0

        node_rating_count.save()