Warning message while running Flask

Question

While I am running Flask code from my command line, a warning is appearing:

Serving Flask app \"hello_flask\" (lazy loading)
* Environment: production
  WARN         


        

Answer 1

I was typing flask run and then saw this message after that I solve this issue with these:

1- Add this text in your myproject/.flaskenv :
FLASK_APP=myapp.py
FLASK_ENV=development
also you should type "pip3 install python-dotenv" for using this file .flaskenv

2-in your project folder type in terminal your flask command which one you use :
flask-3 run

Answer 2

As of Flask 1.x, the default environment is set to production.

To use the development environment, create a file called .flaskenv and save it in the top-level (root) of your project directory. Set the FLASK_ENV=development in the .flaskenv file. You can also save the FLASK_APP=myapp.py.

Example:

myproject/.flaskenv:

FLASK_APP=myapp.py
FLASK_ENV=development

Then you just execute this on the command line:

flask run

That should take care of the warning.

Answer 3

As stated in the Flask documentation:

While lightweight and easy to use, Flask’s built-in server is not suitable for production as it doesn’t scale well and by default serves only one request at a time.

Given that a web application is expected to handle multiple concurrent requests from multiple users, Flask is warning you that the development server will not do this (by default). It recommends using a Web Server Gateway Interface (WSGI) server (numerous possibilities are listed in the deployment docs with further instructions for each) that will function as your web/application server and call Flask as it serves requests.