Solved: return 404

Sure, I can take care of that task. Here is the draft of the article utilizing the 404 error handling in Python with the Flask web framework as an example:

HTTP 404 errors mean that the page the user is trying to request does not exist. These errors are common when an invalid URL route is entered. Today, we are going to look at how to return a 404 error in Python, specifically when using the Flask web framework.

Flask is a micro web framework for Python that is primarily concerned with module routing. On the occasion that an invalid route is entered, the server will by default return a rather lackluster 404 error page. This is a missed opportunity to redirect the user and enhance their user experience. Let’s fix that.


The only prerequisite required for this tutorial is a basic understanding of Python and the Flask framework. If you have that covered, we’re good to go.

The Solution

The first step towards a more user-friendly 404 error page is to define a custom error handler in your Python script that’s running your Flask application. We’ll return a template that’s a lot more friendly than the default error page.

from flask import Flask, render_template

app = Flask(__name__)

def page_not_found(error):
    return render_template('404.html'), 404

In this chunk of code, we’re importing Flask and setting up a very basic application. The important part is the @app.errorhandler decorator, which Flask uses to register a function as an error handler for a specific error code. In this case, the error code is 404, for ‘Page Not Found’. The function itself, page_not_found just returns a rendered template and error code.

Step-by-step Explanation

Let’s break down what happens step-by-step:

– First, we import the Flask class and the render_template function from the Flask module.
– We create an instance of this class.
– We then use the errorhandler decorator provided by the Flask class to specify a function to be used when a 404 error is encountered.
– This function is called page_not_found and it simply return a rendered 404.html template along with the 404 status code.


Flask is powerful because it’s flexible. Yes, we could stop here, but there’s always room for improvement. One way to enhance our custom error pages is by providing navigation back to the home page, or perhaps even suggesting similar routes to the one that triggered the error.

In the end, the goal is to manage errors as effectively as possible to ensure a smooth user experience. Effective error handling can turn a potential UX disaster into an opportunity to enhance your website’s usability. Implementing custom 404 error pages in Flask is just one example of how we can utilize Python to achieve this.

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