Celery: How to ignore task result in chord or chain?

Question

I'm using celery, I have several tasks which needed to be executed in order.

For example I have this task:

@celery.task
def tprint(word):
    print word

And I want to do something like this:

>>> chain(tprint.s('a') | tprint.s('b'))()

Then I get TypeError: tprint() takes exactly 1 argument (2 given).

The same with chord, in this situation which I need a task to be executed after a group of tasks:

>>> chord([tprint.s('a'), tprint.s('b')])(tprint.s('c'))

So how to deal with this situation? I don't care the result of each task, but they need to be executed in order.

---

Add a second parameter won't work:

@celery.task
def tprint(word, ignore=None):
    print word

>>> chain(tprint.s('a', 0) | tprint.s('b'))()

This will print out 'a' and 'None'.

Answer 1

There is a built-in functionality to ignore result in chaining and others - immutable subtask. You can use .si() shortcut instead of .s() or .subtask(immutable=True)

More details here: http://docs.celeryproject.org/en/master/userguide/canvas.html#immutability