using class methods as celery tasks

Question

I’m trying to use the methods of class as the django-celery tasks, marking it up using @task decorator. The same situation is discribed here, asked by Anand Jeyahar.
It’s something like this

class A:
    @task
    def foo(self, bar):
        ...

def main():
    a = A()
    ...
    # what i need
    a.foo.delay(bar) # executes as celery task 
    a.foo(bar) # executes locally

The problem is even if i use class instance like this a.foo.delay(bar) it says, that foo needs at least two arguments, which meens that self pointer misses.

More information:

I can’t convert class to module because of inheritance
Methods are strongly depended on class members, so i can’t make them static
Marking class as the task with @task decorator makes the class a task itself, and it could be possible to execute the methods from run() method, using some argument as a key for method selection, but it’s not exactly what i want.
Creating an instance of class and passing it as self argument to methods changes the way i execute the methods not as celery taks, but as usual methods (i.e. while testing)
I’ve tried to find out how i can register the task dinamically, from constructor for example, but celery shares the code between the workers, so that’s why it seems to be impossible.

Thanks for your help!

Asked By: Thorin Schiffer

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Source

Answer 1

Celery has experimental support for using methods as tasks since version 3.0.

The documentation for this is in celery.contrib.methods, and also mentions some caveats you should be aware of:

https://docs.celeryproject.org/en/3.1/reference/celery.contrib.methods.html

Be aware: support for contrib.methods removed from Celery since 4.0

Answered By: asksol

Answer 2

When you have:

    a = A()

you can do:

    A.foo.delay(a, param0, .., paramN)

Cheers

Answered By: mihaicc

Answer 3

For me the only one that works is celery.current_app because just this passes self to the method.

So this should look like this:

from celery import current_app
from celery.contrib.methods import task_method

class A:
@current_app.task(filter=task_method, name='A.foo')
def foo(self, bar):
    ...

The name must be used if you have method with the same name in different classes.

Answered By: Johnny Wellington

Answer 4

Jeremy Satterfield has a clean and straight forward tutorial to write class based tasks if that’s what you want to accomplish. You can check it here.

The magic is basically extending celery.Task class including a run() method, like something like this:

from celery import Task

class CustomTask(Task):
    ignore_result = True

    def __init__(self, arg):
        self.arg = arg

    def run(self):
        do_something_with_arg(self.arg)

and then run the task like this:

your_arg = 3

custom_task = CustomTask()
custom_task.delay(your_arg)

I am not sure if ignore_result = True part is necessary or not.

Answered By: Gokhan Sari

Answer 5

I ran into a similar situation and decided to wrap class methods within a simple function that would redirect its parameters to an instance of the class and it’s execution of such methods:

class A:
    def foo(self, bar):
       # do this

a = A()

@app.task
def a_wrapper(bar):
    return a.foo(bar)

# probably in a different size with an import in-place:

a_wrapper.delay(bar)

Answered By: Wilmer Gonzalez

using class methods as celery tasks

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