如何在 flask 中运行 app.run() 之前的代码？

Question

I'm new on flask.I configured a server with flask+gunicorn.

the code file called test.py like this:

from flask import Flask
app = Flask(__name__)

@app.route('/')
def test():
    return aa+"world!"

if __name__ == '__main__':
    aa = "hello"
    app.run()

run it using： gunicorn -b 0.0.0.0:8080 test:app

I got a mistake： NameError: name 'aa' is not defined.

I want some codes like variable aa runing before gunicorn.

How to do that？

Answer 1

Put in a small block just before your @app.route and you dont need the last block in the question

 @app.before_first_request
 def _declareStuff():
     global aa
     aa='hello'

Answer 2

Just declare aa outside of " __main__ ", in the global scope of the file.

from flask import Flask
app = Flask(__name__)

@app.route('/')
def test():
    return aa+"world!"

aa = "hello"

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

The code in the if __name__ == '__main__': block executes only if the Python code is run as a script, eg, from the command line. Gunicorn imports the file, so in that case the code in __main__ will not be executed.

---

Note that if it is your intention to modify the value of aa then different requests can produce different results depending on how many requests each gunicorn worker process has handled. eg:

from flask import Flask
app = Flask(__name__)

@app.route('/')
def test():
    global counter
    counter += 1
    return "{} world! {}".format('aa', counter)

counter = 0

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

Run the above script with more than one worker ( gunicorn -w 2 ... ) and make several requests to the URL. You should see that the counter is not always contiguous.

Answer 3

As of Flask 2.2, the @app.before_first_request decorator suggested by Vipluv in their answer is deprecated and will be removed in 2.3.

Deprecated since version 2.2: Will be removed in Flask 2.3. Run setup code when creating the application instead.

The equivalent can be done by manually pushing the app context , as suggested by Enkum :

# In place of something like this
@app.before_first_request
def create_tables():
    db.create_all()
    ...

# USE THIS INSTEAD
with app.app_context():
    db.create_all()