from flask import Flask

app = Flask(__name__)

@app.route("/")
def index():
    return "
Hello!
"

if __name__ == "__main__":
    from waitress import serve
    serve(app, host="0.0.0.0", port=8080)

Here is what the above code is Doing:
1. We’re creating a new Flask object.
2. We’re using the route decorator to tell Flask what URL should trigger our function.
3. We’re defining a function, index(), which is going to return the string “Hello, world!”.
4. We’re adding a bit of code at the bottom of the script to make sure that the application is run when the script is executed.