Here’s a quick way you can combine Dramatiq and APScheduler to automatically schedule tasks to execute at certain times.

Install Dramatiq and APScheduler using pipenv:

pipenv install dramatiq apscheduler

Next, declare a task and decorate it with @cron. We’ll define the cron function afterwards. In a module called tasks.py, add the following code:

import dramatiq

from cron import cron
from datetime import datetime


@cron("* * * * *")  # Run once a minute
@dramatiq.actor
def print_current_datetime():
    print(datetime.now())

Then define the decorator in cron.py:

import importlib

from apscheduler.triggers.cron import CronTrigger

JOBS = []


def cron(crontab):
    """Wrap a Dramatiq actor in a cron schedule.
    """
    trigger = CronTrigger.from_crontab(crontab)

    def decorator(actor):
        module_path = actor.fn.__module__
        func_name = actor.fn.__name__
        JOBS.append((trigger, module_path, func_name))
        return actor

    return decorator

JOBS is where the job definitions are stored. When we run the scheduler from the command line, we’ll iterate over this list and register jobs based on entries made here.

cron just builds a cron trigger and adds a job definition to JOBS.

Now that we have all the components in place, we just need a way to run a scheduler from the command line. In a file called run_cron.py add the following:

import cron
import logging
import signal
import sys
import tasks  # imported for its side-effects

from apscheduler.schedulers.blocking import BlockingScheduler

logging.basicConfig(
    format="[%(asctime)s] [PID %(process)d] [%(threadName)s] [%(name)s] [%(levelname)s] %(message)s",
    level=logging.DEBUG,
)

# Pika is a bit noisy w/ Debug logging so we have to up its level.
logging.getLogger("pika").setLevel(logging.WARNING)


def main():
    scheduler = BlockingScheduler()
    for trigger, module_path, func_name in cron.JOBS:
        job_path = f"{module_path}:{func_name}.send"
        job_name = f"{module_path}.{func_name}"
        scheduler.add_job(job_path, trigger=trigger, name=job_name)

    def shutdown(signum, frame):
        scheduler.shutdown()

    signal.signal(signal.SIGINT, shutdown)
    signal.signal(signal.SIGTERM, shutdown)

    scheduler.start()
    return 0


if __name__ == "__main__":
    sys.exit(main())

Here we set up logging, instantiate a blocking scheduler and register all the jobs that were declared in tasks.py – which is why we import it in the first place, if we didn’t, then the code that registers the jobs would never run. Finally, we add a signal handler to shut down the scheduler whenever the process receives a SIGINT or a SIGTERM.

Run rabbitmq-server then python run_cron.py and dramatiq tasks in a separate terminal and you’re done! You should see your workers print the current time once a minute.