Celery beat args: list vs. tuple

Question

The Celery docs describe how you can pass positional arguments to your beat-scheduled tasks as a list or tuple.

I have a task that takes a single argument, a list of integers:

@shared_task
def schedule_by_ids(ids):
  ...

My celerybeat schedule looks like this:

CELERYBEAT_SCHEDULE = {
    'schedule_by_ids': {
        'task': 'myproj.app.tasks.schedule_by_ids',
        'schedule': crontab(minute='*/10', hour='8-21'),
        'args': ([1,]),
    },
}

My task fails with an "int is not iterable" TypeError. According the my monitor (celery flower) the args are passed as [1].

When I make the args a list, like [[1]], the arg shows up in the monitor as [[1]] and it works fine.

My questions are: How is it passing the args when it is a tuple? Why?

Answer 1

([1,])

That's not a tuple. That's just [1,] in grouping parentheses. If you want a 1-element tuple, you need to put a comma in it like so, to distinguish it from just a parenthesized expression:

([1,],)

I suspect you may have misplaced the comma, and you meant to do this:

([1],)