Flask App Routing

Introduction to Flask App Routing

Routing is a core concept in Flask that allows you to map URLs to functions. When users visit a specific URL in your web application, Flask uses routing to determine which piece of code should handle the request and what response to return.

Understanding Routes in Flask

In Flask, routes are defined using the @app.route() decorator. This decorator associates a URL pattern with a Python function. When a user navigates to that URL, the corresponding function executes and returns content, usually HTML or text.

Creating a Basic Route

Let's consider a simple example where you define a route for the home page:

from flask import Flask

app = Flask(__name__)

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

Here, visiting / triggers the home() function, displaying a welcome message.

Routes with Variable Rules

Flask also supports dynamic routes that accept variables as part of the URL. These variables are captured and passed to the view function as parameters. For example:

@app.route('/user/<username>')
def show_user(username):
    return f'User: {username}'

If you visit /user/Alice, the page will display "User: Alice". This feature enables personalized and dynamic content.

Using Variable Converters

To enforce the type of variables in routes, Flask provides converters like int, float, and path. For instance:

@app.route('/post/<int:post_id>')
def show_post(post_id):
    return f'Post ID: {post_id}'

This route only matches URLs where post_id is an integer, improving URL handling accuracy.

Handling HTTP Methods in Routes

By default, routes respond to GET requests. You can allow other HTTP methods such as POST or DELETE by specifying them in the route decorator:

@app.route('/submit', methods=['GET', 'POST'])
def submit():
    if request.method == 'POST':
        return 'Form submitted!'
    else:
        return 'Please submit the form.'

This flexibility is essential for building interactive web applications.

Summary

Flask’s routing system is simple yet powerful, enabling you to create static and dynamic routes easily. Understanding how to use routes, variable rules, converters, and HTTP methods effectively will help you build organized and scalable Flask web applications.