Why is there no circular import error here?

[dariuscosden]

I'm using this repo as the base for my celery implementation in a project. In my project, I am getting circular import errors, but here there aren't. Shouldn't there be?

You have __init__.py, which imports auth from the views folder. auth in turn has some authentication functions, one of which (register) imports the send_email celery task from emails.py. Finally, emails.py imports celery from __init__.py, therefore making it a circular import.

Am I missing something here? I have a very similar setup and I am getting circular import errors.

[miguelgrinberg]

I'm not sure if we are looking at the same thing, but __init__.py does not import auth in the global scope, it does so inside the create_app() function. That is not the same. Imports in the global scope run very early, by putting the import of auth inside create_app() it is delayed until everything else has been imported.

[dariuscosden]

I thought so too, however in my case I still get a circular import error. Here is a very simplified structure for reference:

./init.py

def create_app():
    app = Flask(__name__)

    # Api
    with app.app_context():
        import server.api.post as post_api
        app.register_blueprint(post_api.bp)

    # Rest of stuff

# Celery
def init_celery(app=None):
    app = app or create_app()

    celery = Celery(broker=app.config["CELERY_BROKER_URL"])
    celery.conf.update(app.config)

    class ContextTask(celery.Task):
        """Make celery tasks work with Flask app context"""

        def __call__(self, *args, **kwargs):
            with app.app_context():
                return self.run(*args, **kwargs)

    celery.Task = ContextTask
    return celery

celery_client = init_celery()

./api/post/init.py

from flask import Blueprint
from server.celery_app import do_background_stuff

bp = Blueprint("post", __name__)

@bp.route("/api/v1/posts", methods=["POST"])
def posts():
    do_background_stuff.delay(10)

./celery_app.py

from server import celery_client

@celery_client.task()
def do_background_stuff():
    print('test')

The issue is ./__init__.py importing api.post, which imports do_background_stuff, and that one imports celery_client from ./__init__.py. It's the same structure as this repo isn't it? And the import is inside of the create_app() function as well. Why do you think I'm getting a circular import error?

Edit
Here is the error for reference

ImportError: cannot import name 'celery_client' from partially initialized module 'server' (most likely due to a circular import) (/server/server/__init__.py)

[miguelgrinberg]

I can't really help with the information that I have. Seems like a pretty standard circular import problem though. If your import is inside create_app() then you must be calling this function too early, before all other imports have executed.

[dariuscosden]

Seems to be the case. I temporarily resolved it by importing the celery task on the line right before where I call it but this isn't what I'd call a solution. I'm going to look into it more. I'll close this issue as it doesn't relate to this repo at this point. Thanks a lot for your answers though!