Troubleshooting 403 Errors with Python Requests Despite Setting User-Agent

When making requests to certain web APIs or websites with Python's requests module, you may encounter 403 Forbidden errors even after explicitly setting a User-Agent header. This frustrating error suggests access is prohibited whether due to missing authentication, blocked IP, or suspicion of spamming or abuse.

Before assuming the worst, first ensure the User-Agent mimics a real desktop browser's typical user agent string. For example:

headers = {'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36'}

Some APIs may be restricting access based on IP address ranges, blocking all requests from cloud providers/data centers. Try routing requests through a residential proxy or VPN to determine if this is the cause.

For sites utilizing Cloudflare protection, setting a CF-Connecting-IP header to your outbound IP address may help prove you are not a spam bot.

In some cases the target website may have an allowance for a certain number of requests per day before cutting off access. Slowing request rate and verifying with the provider if quotas or limits are in place can avoid unpredictable 403s.

Ultimately, explicitly registering API keys for services, using appropriate authorization mechanisms, or whitelisting server IP addresses may be necessary steps to get out of 403-jail. The error doesn't always indicate something wrong on your end!