Flask is a simple web framework based on Werkzeug. It's easy to build HTTP GET/POST requests. If you have a scenario where you want to develop a RESTful server, Flask can solve your problem fast. The official website of Flask is http://flask.pocoo.org. You can install Flask using pip. Type this command:

    $ pip install Flask

For testing, we can create a simple-to-handle HTTP GET request. Create a Python file, called ch04_flask.py. Write the following program:

from flask import Flask 
app = Flask(__name__) 
 
@app.route("/") 
def hello(): 
    return "Hello,Flask!" 
 
@app.route('/ads/<int:ads_id>') 
def show_post(ads_id):     
    return 'Adversiting id %d' % ads_id 

This program will handle HTTP GET requests: / and /ads/<id>.

To run the program, you can type this command:

    $ FLASK_APP=ch04_flask.py flask run

It shows a running web server on a specific port, by default 5000. Now you can open a browser and navigate to http://localhost:5000 and try again to navigate to http://localhost:5000/ads/10. You can see the sample browser and program output here:

For further information about Flask development, I recommend you read the Flask documentation at http://flask.pocoo.org/docs/. Some program samples are provided to help you get started.