Pass another object to the main flask application

Question

I got a doubt about how to pass an object to a flask app in the correct way.

The idea is simple.

I wan to create an api for my application, which means that http requests processed by my flask application will trigger methods in my main application.

For that, I need flask to be aware of my other process, one way or another.

Currently, I have something like :

if __name__ == '__main__':
    Logger = MyProcess()
    app.run()

I need to be able to do something like that :

@app.route('/nb_trendy')
def nb_trendy():

    res = Logger.get_trendy()
    return jsonify(res)

which means that I either need to either give a handle on Logger to app, or directly define Logger inside app.

But in each of the solutions I can find, I need to create a class that inherits app, to either override __init__() and takes objects as parameters, or modify the run() method.

the current way I would do it is though :

class MyFlask(Flask):
    def __init__():
        Flask.__init__()
        Logger = MyProcess()

Is this also the way you would do it, or is there a better way to do this?

Thanks!

Here is a more general version of this question: Web API in Flask

Answer 1

Take a look at application factories, which should do what you're looking for. You'd create a factory that returned your Flask app that you'd send the logger to - something like this:

def create_app(logger_instance):
    app = Flask(__name__)
    app.config['LOGGER'] = logger_instance
    return app

And then in your runserver.py, you'd create and pass in the logger:

from yourapp import create_app
if __name__ == '__main__':
    logger = MyProcess()
    app = create_app(logger)
    app.run()

Once that's done, your app can refer to the logger inside app.config['LOGGER'].

Answer 2

You might want to use flask app context for this

from flask import _app_ctx_stack 

def getLogger():
    appContext = _app_ctx_stack.top
    logger = getattr(appContext, "Logger", None)
    if logger is None:
        logger = MyProcess()
        appContext.Logger = logger
    return logger

....

@app.route('/nb_trendy')
def nb_trendy():
    logger = getLogger()
    res = logger.get_trendy()
    return jsonify(res)

more insight from Armin on that: https://speakerdeck.com/mitsuhiko/advanced-flask-patterns