Flask Routing in Python with Basic Examples: String, Integer and Float Values


Flask, a lightweight and versatile web framework for Python, is celebrated for its ease of use and flexibility, making it an ideal choice for developers embarking on web application projects. At the heart of Flask’s simplicity and power lies its routing system, a fundamental aspect that enables developers to connect client requests to server responses with remarkable efficiency. Flask routing is the mechanism by which specific URL patterns are matched with corresponding Python functions within the application, effectively dictating how the application responds to various client requests. This article delves into the intricacies of Flask routing, offering insights into its operation and utility in web development.

Routing in Flask is not just a mere pathway for handling URLs but a gateway to creating dynamic, user-centric web applications. It stands out for its ability to handle both static and dynamic URLs, allowing developers to pass parameters through URL paths directly into view functions. This feature is a testament to Flask’s adaptability, catering to a range of web development needs from simple web pages to complex RESTful APIs. Furthermore, Flask’s routing system is elegantly designed with decorators, making code not only more readable but also easier to maintain and debug.

An essential aspect of Flask routing is its support for various HTTP methods, enabling the development of applications that can respond differently to GET, POST, and other request types. This flexibility is crucial for creating modern web applications that interact with databases and third-party services. Additionally, the framework’s built-in development server and debugger aid in efficient troubleshooting and testing of routes, enhancing the development experience.

This article aims to provide a comprehensive overview of Flask routing, from its basic syntax and usage to more advanced features like dynamic URL rules and HTTP method handling. Whether you’re a seasoned developer or just starting out, understanding Flask routing is key to harnessing the full potential of this powerful framework in your web development endeavors.

What is Flask Routing:

Flask routing is a fundamental aspect of the Flask web framework, a lightweight and flexible Python framework used for developing web applications. Essentially, routing in Flask involves mapping the URLs of web requests to specific Python functions, known as view functions, within the application. This mechanism is crucial because it determines how a Flask application responds to a client’s request for a specific endpoint or URL. Each route in Flask is defined using the @app.route() decorator, which is placed above the view function. The decorator takes the URL path as an argument, thereby linking the URL to the corresponding function. This design allows developers to easily define how their application responds to different URLs, making it straightforward to create both static and dynamic web pages. Dynamic routing is one of Flask’s strengths, as it supports variable rules in URL paths, enabling the passing of parameters to view functions directly from the URL. For instance, a route like @app.route(‘/user/<username>’) dynamically accepts a username, making the application more interactive and adaptable. Flask’s routing system is both powerful and user-friendly, offering a seamless way to control the flow of web traffic within an application, and is a key reason for Flask’s popularity in the web development community.

Properties of Flask Routing:

Flask routing, a core feature of the Flask web framework, possesses several distinctive properties that make it highly effective and popular for web application development. Here’s a detailed look into these properties:

Simplicity and Readability: Flask’s routing mechanism is straightforward. By using Python decorators, specifically @app.route(), it links URLs to corresponding Python functions (view functions) in an easily readable and maintainable manner. This simplicity reduces the learning curve for new developers and enhances code clarity.

Dynamic URL Routing: One of Flask’s powerful features is its support for dynamic URLs. It allows parts of the URL to be variable, which are then passed as arguments to the view functions. For example, in a route like @app.route(‘/user/<username>’), the <username> part is dynamic, enabling the function to handle requests for any user by that parameter.

HTTP Method Support: Flask routes can be configured to respond to different HTTP methods, such as GET, POST, PUT, and DELETE. This is crucial for RESTful API development, where the method type dictates the operation performed.

URL Building: Flask’s url_for() function generates URLs to a specific function, which is useful for dynamic URL generation. This is particularly helpful in templates where you need to insert URLs that might change over time.

Blueprints for Scalability: For larger applications, Flask offers Blueprints. These are templates for Flask routes that allow for scalability and better organization. Blueprints enable the separation of different parts of an application, like authentication, admin, and main application logic, into distinct components.

Error Handling: Flask provides options to handle HTTP errors elegantly. Custom error pages for different HTTP status codes (like 404 Not Found) can be defined using routing, improving the user experience.

Decorator Flexibility: Besides @app.route(), Flask allows for custom decorators, giving developers the flexibility to add additional functionality like authentication checks, logging, or request preprocessing to routes.

Secure and Customizable: Flask ensures security in routing, such as avoiding trailing slashes ambiguity. Also, developers have the freedom to customize routing behavior to suit their application’s needs.

In summary, Flask routing’s properties of simplicity, dynamic URL handling, method support, and scalability, among others, contribute to its versatility and popularity in building efficient and maintainable web applications.

Built-in function in Flask Routing

Flask, a lightweight Python web framework, offers a built-in routing mechanism that is both powerful and user-friendly. The centerpiece of Flask’s routing system is the @app.route() decorator, a built-in function that connects URL patterns to Python functions in your application. This decorator is the primary tool for defining routes in a Flask application, making it simple and intuitive to map client requests to server responses.

The @app.route() function takes the URL path as a primary argument. This path is a string that specifies the URL rule, helping Flask to identify which function to execute when a specific URL is accessed. For example, @app.route(‘/home’) maps the URL ‘/home’ to a view function that follows the decorator. This allows for easy creation and management of both static and dynamic web pages.

Flask routing also supports dynamic URL parameters. By using variable parts in the route definition, such as @app.route(‘/user/<username>’), Flask can handle URLs that differ only in certain variable sections. These variable sections in the URL are then passed to the view function as arguments, enabling the function to perform operations based on these dynamic parameters.

In addition to URL mapping, the @app.route() function allows specifying HTTP methods like GET, POST, PUT, and DELETE, which are essential for creating RESTful applications. By default, routes only respond to GET requests, but this can be altered by providing a methods argument to the route decorator, for example, @app.route(‘/submit’, methods=[‘POST’]).

Another built-in function in Flask’s routing system is url_for(). This function generates URLs to specific functions, which is extremely helpful in templates for generating dynamic links. It works by accepting the name of a view function and, optionally, some arguments; it then returns the corresponding URL path defined in the application’s routes.

Flask’s routing mechanism, primarily through its @app.route() decorator and supporting functions, provides a seamless and efficient way to direct web traffic within an application. Its simplicity, coupled with powerful features like dynamic URL patterns and HTTP methods handling, makes it a cornerstone of the Flask framework.

if you don’t know how to install and run the Python Flask application then read my previous article.

Python Flask web framework Installation and Hello World Application

Some Basic Examples of Flask Routing:

Basic example print message using Python Flask Routing:

Steps to Run the Application

Save this code in a file named

Open your terminal or command prompt.

Navigate to the directory where is located.

Run the application by typing python

Open a web browser and go to

This will display the message “Welcome to the Programming Digest Home Page!” in your browser, demonstrating a basic Flask route. This example is as straightforward as it gets with Flask, perfect for understanding the fundamental concept of routing in Flask.

Flask Routing in Python

How to use integer value in Python Flask Routing

To use an integer value in Flask routing, you can define dynamic routes that accept integer parameters. Flask allows you to specify parts of the URL as variable sections, which can be captured and passed to your view function as arguments. For integer values, you specify the variable part in the route with <int:variable_name>.

How to Test

Save this script in a file, say

Run the script using Python (python

Open a web browser and visit, replacing 5 with any integer you wish to square.

This route will calculate the square of the integer you pass in the URL and display the result. The <int:number> in the route tells Flask to expect an integer value and pass it to the square function as the number parameter. This feature is incredibly useful for creating dynamic web applications that respond to user input directly through the URL.

Flask Routing in Python

How to use float value in Python Flask Routing

Using a float value in Flask routing is similar to using an integer value, but with the key difference that you specify the variable part of the URL to be a float. This is done by using <float:variable_name> in the route definition. This allows the route to accept floating-point numbers as part of the URL and pass them to the view function.

Testing the Application

Save this script in a file, for example,

Run the script using Python by executing python in your terminal.

Open a web browser and navigate to, replacing 60.7 with any float value of your choice.

This route will calculate and display half of the float value you pass in the URL. The <float:number> part in the route tells Flask that this segment of the URL is a floating-point number and should be passed to the half function as the number parameter. This capability is particularly useful for creating dynamic routes in your Flask application that can handle and process floating-point numbers directly from the URL.

Flask Routing in Python

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