Only get len once

Author: blueyed

pytest_django/fixtures.py

@@ -345,12 +345,13 @@ def _assert_num_queries(config, num, exact=True):
     verbose = config.getoption('verbose') > 0
     with CaptureQueriesContext(connection) as context:
         yield
-        failed = num != len(context) if exact else num < len(context)
+        num_queries = len(context)
+        failed = num != num_queries if exact else num < num_queries
         if failed:
             msg = "Expected to perform {} queries {}{}".format(
                 num,
                 '' if exact else 'or less ',
-                'but {} were done'.format(len(context))
+                'but {} were done'.format(num_queries)
             )
             if verbose:
                 sqls = (q['sql'] for q in context.captured_queries)