Can't get Celery run_every property to work

Question

I'm trying to create some Celery Periodic Tasks, and a few of them need to have the ability to change the run_every time at runtime. The Celery documentation says I should be able to do this by turning the run_every attribute into a property (http://packages.python.org/celery/faq.html#can-i-change-the-interval-of-a-periodic-task-at-runtime).

Here is what I'm doing:

class ParseSomeStuffTask(PeriodicTask):

    def run(self, **kwargs):
        # Do stuff

    @property
    def run_every(self):
        if datetime.now().weekday() in [1, 2, 3]:
            return timedelta(minutes=15)
        else:
            return timedelta(seconds=40)

Unfortunately, when I turn on celerybeat, I get the following error:

[Thu Sep 09 15:44:40 2010: CRITICAL/828]: celerybeat raised exception : 'datetime.timedelta' object has no attribute 'is_due'

It then shuts down. The Celery documentation doesn't really go into what to return when making run_every a property, and I haven't had any luck searching Google. Celery changelogs say its been able to change a Periodic Task's interval at runtime since version 1.0.0.

Dev. Environment:

• Python 2.6.5
• Django 1.2.1
• Celery 2.0.2

Answer 1

Celery 2.0 supports different schedule behaviors. There's celery.task.schedules.schedule and celery.task.schedules.crontab.

You have to return one of these, or make your own subclass of schedule.

from celery.task.schedules import schedule

@property
def run_every(self):
    if datetime.now().weekday() in [1, 2, 3]:
        return schedule(timedelta(minutes=15))
    else:
        return schedule(timedelta(seconds=40))

The run_every attribute will be automatically converted at instantiation, but not later.