CODEWITHSUNDEEP
pythonflask
KexAri
KexAri

Reputation: 3977

I don't need the run() method in a Flask application?

I have a Flask application setup on my linode with a directory structure like so:

|--------flask-test
|----------------app
|-----------------------static
|-----------------------templates
|-----------------------venv
|-----------------------__init__.py
|-----------------------main.py

my __init__.py is:

# __init__.py
from flask import Flask
from main import main
app = Flask(__name__)
app.register_blueprint(main)
app.run()

and main.py like so:

# main.py
from flask import Blueprint

main = Blueprint('main',__name__)
@main.route("/")
def hello():
    return "Hello World!"

@main.route("/england/")
def england():
    return "Hello England!"

If I run the app locally there are no issues. If I go to my server address in the web browser I get an internal server error. However if I remove the line: app.run from __init__.py it works fine. Why is this? Why do I not need the run method?

Upvotes: 5

Views: 3314

Answers (2)

Cfreak
Cfreak

Reputation: 19319

You should do

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

The reason is that Apache or NGINX or some other web server loads your app directly on the server but app.run() runs flask's internal web-server so you can test your app.

EDIT: Since someone came by and upvoted this very old answer (thanks!) I will point out that there is no reason to include this convention. Flask includes a run command for testing.

Instead of the old way:

python yourapp.py

you now do:

flask --app yourapp run

Or if you name the main controller of your app "app.py" you can commit the --app flag.

Upvotes: 10

Graham Dumpleton
Graham Dumpleton

Reputation: 58563

It is a bit odd to have app.run() inside of the __init__.py file, normally it would be in a separate application script you run, where it would be written as:

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

This way app.run() is only called when that script is executed as the application.

This is necessary because you do not want app.run() called when hosting under a WSGI server such as mod_wsgi or gunicorn. When using such WSGI servers, even if reusing the same script file as holder of the WSGI application entrypoint, __name__ wouldn't be set to __main__ but the basename of the script file. This ensures that app.run() isn't called where it is the separate WSGI server which is running the web server component.

Upvotes: 5

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