They are probably just checking headers such as user agent and cookies. Would copy whatever your normal browser sends and put it in the urllib.request. If that doesn’t work, then it is likely more sophisticated.
$ curl -s -I 'https://www.sfgate.com/' -H 'User-Agent: curl/7.54.1' | head -1
HTTP/2 403
$curl -s -I 'https://www.sfgate.com/' -H 'User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:109.0) Gecko/20100101 Firefox/113.0' | head -1
HTTP/2 200
One "trick" is that Firefox (and I assume Chrome?) allow you to copy a request as curl - then you can just see if that works in the terminal, and if it does you can binary search for the required headers.
