Django + Celery: How to run a task after subtasks from different scheduled Tasks are finished

Question

I'm currently building a webapp with Django and Celery. I have one task (sometask) that adds an unknown number of other tasks(othertask) in a for loop to the queue. Now I don't understand how I can run another Task(task3) after sometask with all the subtasks are done.

I understand that you can chain tasks for example, but if I chain othertask to sometask it will run before the subtasks are done. Could someone please give me some input on how to get it done the way I described?

Example of my tasks.py

@shared_task(bind = True) 
def sometask(self):
    for whatever:
       othertask.delay()
    return "done"

@shared_task(bind = True) 
def othertask(self):
    pass

@shared_task(bind = True) 
def task3(self):
    pass

Celery.py:

app.conf.beat_schedule = {
   'weekly':{
       'task': 'webapp.tasks.sometask',
       'schedule': crontab(minute=0, hour=23, day_of_week='sat'),
   }
}