How to call a function before starting the flask app?

Asked Jan 11 '22 at 12:10

Active Jan 11 '22 at 12:10

Viewed 34 times

I want to execute a function before my flask app starts and this is what I did for achieving my goal.

# flask_app.py

def dummy_func():
    print('some dummy text')

def create_app() -> Flask:
    app = Flask(__name__)
    # doing somethings
    dummy_func()
    return app

if __name__ == '__main__':
    app = create_app()
    app.run()

With this example, everything works fine but it calls dummy_func() two times and I don't want this to happen.

# flask run
 * Serving Flask app 'run' (lazy loading)
 * Environment: development
 * Debug mode: on
some dummy text
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
 * Restarting with stat
 * Debugger is active!
 * Debugger PIN: 136-570-428
some dummy text

And my question is why it has happened and how can I fix that?

asked Jan 11 '22 at 12:10

Iman Hosseini Pour

Isn't it the case of just moving the function call to the line between `app = create_app()` and `app.run()`? – accdias Jan 11 '22 at 12:15
"Restarting with stat" sounds like a good point where to start the research – Marco Jan 11 '22 at 12:21
1

WSGI servers are usually using worker processes. When one is spawned it will rerun the code and get a new `app` instance. In development there is usually a master and one worker, in a production setup there can be multiple workers. You can to take this into account. – Klaus D. Jan 11 '22 at 12:23
You probably want the [before_first_request](https://flask.palletsprojects.com/en/2.0.x/api/#flask.Flask.before_first_request) hook. – brunns Jan 11 '22 at 12:43
@accdias I did that but it didn't work. – Iman Hosseini Pour Jan 11 '22 at 18:10
@brunns No, I don't want that – Iman Hosseini Pour Jan 11 '22 at 18:13

How to call a function before starting the flask app?

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