code: def review_score(self, reviewer, product):
          
          return self._g.retrieve_review(reviewer, product).score
docs: Find a review score from a given reviewer to a product.
  
          Args:
            reviewer: Reviewer i.e. an instance of :class:`ria.bipartite.Reviewer`.
            product: Product i.e. an instance of :class:`ria.bipartite.Product`.
  
          Returns:
            A review object representing the review from the reviewer to the product.