1. Introduction

In the realm of web development, Flask, a micro web framework in Python, has become a popular choice due to its simplicity and flexibility. This tutorial is designed to deepen your understanding of Flask, focusing specifically on routing and URL mapping.

By the end of this tutorial, you will learn:
- How to define routes in Flask
- How to create views for those routes
- How URL mapping works in Flask

It is recommended that you have a basic understanding of Python programming and have Flask installed on your local environment.

2. Step-by-Step Guide

One of the first things to understand in Flask is the concept of routes. Routes are essentially the different URLs that your application responds to. Each route is associated with a function, which Flask calls a view function.

In Flask, you define a route with a decorator, @app.route(), where app is your Flask application instance.

Defining a Route

Here's a simple example of a Flask application with one route:

from flask import Flask
app = Flask(__name__)

@app.route('/')
def home():
    return "Hello, Flask!"

In this code, @app.route('/') is a decorator that tells Flask to call the following function (home()) whenever a user visits the main ('/') URL of your application.

URL Mapping

URL mapping is the process of associating a URL and HTTP method (like GET or POST) with a specific function in your application. In Flask, this is done automatically when you define a route.

Here are a few tips to keep in mind:
- Routes are matched in the order they are defined.
- It's recommended to define your routes in a logical and organized way.

3. Code Examples

Basic Route

Here is an example of a basic route:

from flask import Flask
app = Flask(__name__)

@app.route('/')
def home():
    return "Welcome to the Homepage!"

In this example, when you visit the main URL ('/') of your application, Flask will call the home() function and return "Welcome to the Homepage!" as the response.

Route with Variable

Routes can also include variables. Here's an example:

@app.route('/user/<username>')
def show_user_profile(username):
    return 'User %s' % username

This route will respond to any URL of the form '/user/[username]'. The specified [username] will be passed as a string to the show_user_profile function.

4. Summary

In this tutorial, we have covered Flask routing and URL mapping. We have learned how to define routes, create views for those routes, and understand how URL mapping works in Flask.

For further learning, you can explore Flask's documentation or other online resources. You can also experiment with creating your own routes and functions in a Flask application.

5. Practice Exercises

To reinforce your understanding, here are some practice exercises:

1. Create a Flask application with three routes: '/', '/hello', and '/user/[username]'. The '/' route should return "Main page", the '/hello' should return "Hello, World!", and the '/user/[username]' should return "User: [username]", where [username] is a variable.

2. Create a Flask application with a route that responds to both GET and POST requests.

Solutions for these exercises are available online. It's recommended to try solving them on your own before looking at the solutions. This will help you gain a practical understanding of Flask routing and URL mapping.