Document that return values of the task handlers (on_success, on_failure,

on_retry) is ignored.

celery/task/base.py

@@ -345,6 +345,8 @@ class Task(object):
         :param args: Original arguments for the retried task.
         :param kwargs: Original keyword arguments for the retried task.
 
+        The return value of this handler is ignored.
+
         """
         pass
 
@@ -357,6 +359,8 @@ class Task(object):
         :param task_id: Unique id of the failed task.
         :param args: Original arguments for the task that failed.
         :param kwargs: Original keyword arguments for the task that failed.
+        
+        The return value of this handler is ignored.
 
         """
         pass
@@ -371,6 +375,8 @@ class Task(object):
         :param args: Original arguments for the executed task.
         :param kwargs: Original keyword arguments for the executed task.
 
+        The return value of this handler is ignored.
+
         """
         pass