How do I fix 'Popped wrong app context' in Flask with APScheduler - python-3.x

Question

I'm adding background tasks with APScheduler on runtime depending on an API call. In other words, there are no background tasks when the app, starts. When user makes call on an API, tasks are added on runtime. But I'm getting an error that says:
AssertionError: Popped wrong app context
The application works just fine if I comment out the lines where background tasks are scheduled.
My app structure is as follows:
/project
manage.py
requirements.txt
/app
/models
/routes
/utils
/api
config.py
__init__.py
My manage.py file looks like this:
app = create_app('dev')
app.app_context().push()
manager = Manager(app)
migrate = Migrate(app, db, render_as_batch=True)
manager.add_command('db', MigrateCommand)
with app.app_context():
scheduler = BackgroundScheduler()
scheduler.start()
#manager.command
def run():
app.run()
atexit.register(lambda: scheduler.shutdown())
if __name__ == '__main__':
manager.run()
init.py inside app folder is:
from flask import Flask
from flask_restful import Api
from flask_sqlalchemy import SQLAlchemy
from email_scheduler.routes.routes import set_routes
from .config import config_by_name
# from app.models.task import TaskModel
db = SQLAlchemy()
def create_app(config_name):
app = Flask(__name__)
app.config.from_object(config_by_name[config_name])
api = Api(app)
set_routes(api)
from email_scheduler.models.api_models import TaskModel, User
db.init_app(app)
with app.app_context():
db.create_all()
return app
My api.py file is:
class SignUp(Resource):
def clean_scheduling_time(self, schedule_time):
day = schedule_time.split(' ')[0].lower()[:3]
hour, mins = schedule_time.split(' ')[1].split(':')
return day, hour, mins
def post(self):
args = user_parser.parse_args()
username, password = args.get('username'), args.get('password')
schedule_time, email_to = args.get('schedule_time'), args.get('email_to')
if username is None or password is None:
abort(400) # missing arguments
from email_scheduler.models.api_models import User
if User.query.filter_by(username=username).first() is not None:
abort(400) # existing user
user = User(username=username, schedule_time=schedule_time.split(' ')[1], email_to=email_to)
user.hash_password(password)
user.save_to_db()
from manage import scheduler
from email_scheduler.utils.utils import send_email
day, hour, mins = self.clean_scheduling_time(args.get('schedule_time'))
trigger = CronTrigger(day_of_week=day, hour=int(hour), minute=int(mins))
scheduler.add_job(send_email, trigger=trigger)
print(scheduler.get_jobs())
return make_response(jsonify({'username': username}), 200)
What's weird is that even though I get this error on the terminal, the task somehow gets scheduled and is run. And if I take out the code from api that schedules the tasks, the API runs just fine. What am I doing wrong?

Answer 1

The problem is in your manage.py file.
You're running the following line globally:
app.app_context().push()
Which you correctly need for the worker to have access to app context. Move it inside the function that the worker calls.
Ie NOT this:
app = create_app()
app.app_context().push()
def your_async_fn():
# your code for the worker...
But this:
def your_async_fn():
app = create_app()
app.app_context().push()
# your code for the worker...