Flask not activating debug mode

Question

I am getting started with flask, I am trying to follow some tutorials, but I have been unable to run Flask app in debug mode.

I tried the simplest code I found:

from flask import Flask
app = Flask(__name__)

app.debug = True
# I have also tried with a configuration
# app.config.from_object('config')
# file with constant
# DEBUG = True

@app.route('/')
def hello_world():
    return 'Hello World!'

Then I run

export FLASK_APP=hello_world.py
flask run

But I allways get this output

 * Serving Flask app "hello_world.py"
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: off
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

When I run print(app.debug) I get False

This is the output of pip freeze:

click==7.1.2
Flask==1.1.2
itsdangerous==1.1.0
Jinja2==2.11.2
MarkupSafe==1.1.1
Werkzeug==1.0.1

And I have python 3.8.2

Answer 1

I have tried the below steps and it worked for me.

Have added these lines of codes to my app.py file.

if __name__ == "__main__":
    app.run(debug=True)

Then I ran the program from the Terminal using the command line

python3 app.py

and it worked.

Please find the below screenshot

Answer 2

Try This:

When you run,

export FLASK_APP=hello_world.py

Run this command after the above,

export FLASK_DEBUG=1

Finally,

flask run

I hope this would start the debug mode.

Answer 3

if you are using windows just type the following in your terminal :
in PowerShell:

$env:FLASK_ENV = "development"
flask run

in command prompt :

C:\path\to\app>set FLASK_ENV=development
flask run

and for mac you probably need to run this :

$ export FLASK_ENV=development
$ flask run

enjoy !!