Trying to speed up convert mongo into dataframe

cdplib/db_handlers/MongodbHandler.py

@@ -320,13 +320,13 @@ class MongodbHandler:
             if index % chunksize == 0:
                 frames.append(pd.DataFrame(records))
                 records = []
-                
+
         if records:
             frames.append(pd.DataFrame(records))
         return_df = pd.concat(frames, axis=0, sort=False)
 
         if index is not None:
-                df.set_index(index, inplace=True)
+                return_df.set_index(index, inplace=True)
 
         self._log.info(('{} Rows were fetched from {}. DataFrame conversion is done, took {} seconds').format(len(return_df.index), collection_name if collection_name is not None else 'the database', time.time()-start_time))