code: def sims_by_id(self, docid):
          
          result = self.id2sims.get(docid, None)
          if result is None:
              self.qindex.num_best = self.topsims
              sims = self.qindex.similarity_by_id(self.id2pos[docid])
              result = self.sims2scores(sims)
          return result
docs: Find the most similar documents to the (already indexed) document with `docid`.