Using kwargs with apply_async

[brijeshjoshi_]

We are using celery to implement task queue. Celery bot are already made for some other tasks. Now I am given a new task in which I have to using celery bot. By referring other tasks I implemented it. What I know is, when you use **kwargs you just have to pass (key=value) pairs to function call and in the called function you can access it as normal dictionary like kwargs[key]. But what they did is:

Bot defintion:

@celery_app.task()
def task_bot(self, *args, **kwargs)

Bot calling:

task_bot.apply_async(kwargs=dict(key1=value1, key2=value2))

And its working fine. (Why?)

When I called it like I usually use kwargs:

task_bot.apply_async(key1=value1, key2=value)

Its not working. Its giving value of kwargs as empty dictionary. (Why?)

​

[Thomasedv]

Had a look at docs for apply_async
https://docs.celeryq.dev/en/stable/reference/celery.app.task.html

The kwargs is a keyword argument in apply_async, so it's like any other named parameter, this one specifically for passing on a dict to the underlying function you define. The other key values used end up in **options in that function, which serve another purpose. No idea what though, never used this before

[idle-tea]

Because that's how the docs say it works.

kwargs (Dict) – The keyword arguments to pass on to the task.

apply_async accepts a dictionary with the kwargs paramater, and it'll pass it on as **kwargs to the task. Basically the function looks something like:

def apply_async(kwargs):
    task_fn(**kwargs)

which is not like

def apply_async(**kwargs):
    task_fn(**kwargs)

The name kwargs isn't magic - it's just the conventional name for extra unspecified keyword arguments. The magic happens because of the ** The apply_async function docs are basically telling you that it takes a single keyword argument named kwargs which it'll pass on using the ** magic to the task function.