app.py

from flask import Flask        #import flask

#The app object
app = Flask(__name__)          #create an instance of the app taking in the script name

#route
@app.route('/')                #decorates the first view function
def hello_world():
    """Print 'Hello, world!' as the response body."""
    return 'Hello, world!'
if __name__ == '__main__':
    app.run(debug=True)