Troubleshooting HTTP 404 Errors with Python's urllib

Encountering HTTP 404 errors when trying to access web pages with Python's urllib module can be frustrating. This guide will walk through some common causes and solutions for debugging 404 errors.

The 404 status code indicates that the requested URL cannot be found on the server. There are a few possible reasons you might encounter 404 errors with urllib:

Typos in the URL

Double check that the URL you are trying to access is typed correctly without any typos. For example:

import urllib.request

url = 'https//www.example.com' # Typo - missing ':' after https
response = urllib.request.urlopen(url)

This would fail with a 404 error because of the missing colon.

Incorrect URL Path

Verify that the page or endpoint you are trying to access exists on the target server. For example, accessing /invalidpath could 404 if that path is not defined.

Resources Moved or Deleted

The page you are trying to reach may have been removed or relocated on the server, causing a 404. Check with the website maintainers if the URL previously worked.

Handling 404s

You can handle 404 errors gracefully in your Python code instead of crashing:

import urllib.error
import urllib.request

try:
  response = urllib.request.urlopen("http://www.example.com/missing")
except urllib.error.HTTPError as e:
  print(e.code) # Print error code
  print(e.read()) # Print error response body

This will print 404 and the HTML error page while allowing your program to continue.

In summary, double checking the URL, path, and availability of resources can help resolve 404 issues with Python's urllib. Proper exception handling allows you to account for 404s in your code.