code: def index_documents(self, fresh_docs, model):
          
          docids = fresh_docs.keys()
          vectors = (model.docs2vecs(fresh_docs[docid] for docid in docids))
          logger.info("adding %i documents to %s" % (len(docids), self))
          self.qindex.add_documents(vectors)
          self.qindex.save()
          self.update_ids(docids)
docs: Update fresh index with new documents (potentially replacing old ones with
          the same id). `fresh_docs` is a dictionary-like object (=dict, sqlitedict, shelve etc)
          that maps document_id->document.