what export FLASK_APP=app.py does code example

Example 1: run flask app from command line

# For bash do this:
set FLASK_APP=<app_name>

# For powershell do this:
$env FLASK_APP=<app_name>

# Run it like this
flask run

Example 2: run flask app from script

# I am assuming that you have configured the app name as "app"

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