Fixed #27513 -- Made Signal.send()/send_robust() a tiny bit faster.

django/dispatch/dispatcher.py

@@ -185,14 +185,13 @@ class Signal(object):
 
         Returns a list of tuple pairs [(receiver, response), ... ].
         """
-        responses = []
         if not self.receivers or self.sender_receivers_cache.get(sender) is NO_RECEIVERS:
-            return responses
+            return []
 
-        for receiver in self._live_receivers(sender):
-            response = receiver(signal=self, sender=sender, **named)
-            responses.append((receiver, response))
-        return responses
+        return [
+            (receiver, receiver(signal=self, sender=sender, **named))
+            for receiver in self._live_receivers(sender)
+        ]
 
     def send_robust(self, sender, **named):
         """
@@ -218,12 +217,12 @@ class Signal(object):
         receiver. The traceback is always attached to the error at
         ``__traceback__``.
         """
-        responses = []
         if not self.receivers or self.sender_receivers_cache.get(sender) is NO_RECEIVERS:
-            return responses
+            return []
 
         # Call each receiver with whatever arguments it can accept.
         # Return a list of tuple pairs [(receiver, response), ... ].
+        responses = []
         for receiver in self._live_receivers(sender):
             try:
                 response = receiver(signal=self, sender=sender, **named)

django/test/signals.py

@@ -8,7 +8,7 @@ from django.core.signals import setting_changed
 from django.db import connections, router
 from django.db.utils import ConnectionRouter
 from django.dispatch import Signal, receiver
-from django.utils import timezone
+from django.utils import six, timezone
 from django.utils.functional import empty
 
 template_rendered = Signal(providing_args=["template", "context"])
@@ -127,9 +127,9 @@ def file_storage_changed(**kwargs):
 def complex_setting_changed(**kwargs):
     if kwargs['enter'] and kwargs['setting'] in COMPLEX_OVERRIDE_SETTINGS:
         # Considering the current implementation of the signals framework,
-        # stacklevel=5 shows the line containing the override_settings call.
+        # this stacklevel shows the line containing the override_settings call.
         warnings.warn("Overriding setting %s can lead to unexpected behavior."
-                      % kwargs['setting'], stacklevel=5)
+                      % kwargs['setting'], stacklevel=5 if six.PY2 else 6)
 
 
 @receiver(setting_changed)