How do I set a callback in celery

Question

I want to add callback to a function so that when it returns it can call a regular python function,

My Task

@celery.task                                                                                                                            
def add(x, y):                                                                                                                         
    return x + y 

How I want to use it:

from __future__ import print_function
delay.add(2, 3 ,callback=lambda x: print x) 

Instead of the lambda it can be any function that its not defined in the celery tasks but where the task is called from.

Answer 1

You can only link tasks in this case:

add.apply_async((2, 3), link=other_task.s())

which is the same as:

(add.s(2, 3) | other_task.s())()

Waiting for the task to complete makes the task synchronous, so the call you want would be equivalent to:

(lambda x: print(x))(add.delay(2, 3).get())

Which would block the current process until the task returns. If you don't want the process to block then you would have to write a dedicated thread to wait for results and calling your callbacks.

Or you can use eventlet/gevent and pretty much write normal code.