Errors in web applications

Usually, when a Python WSGI web application crashes, you get a traceback in the Terminal and an empty path in your browser.

That doesn't make it very easy to debug what's going on and unless you explicitly check your Terminal, it might be easy to miss that your page is not showing up because it actually crashed.

Luckily, the Python standard library provides some basic debugging tools for web applications that make it possible to report crashes into the browser so you can see them and fix them without having to jump away from your browser.

How to do it...

The cgitb module provides tools to format an exception and its traceback as HTML, so we can leverage it to implement a WSGI middleware that can wrap any web application to provide better error reporting in the browser:

import cgitb
import sys

class ErrorMiddleware:
    """Wrap a WSGI application to display errors in the browser"""
    def __init__(self, app):
        self.app = app

    def __call__(self, environ,...