What I mean is, if I go to "www.yahoo.com/thispage", and yahoo has set up a filter to redirect /thispage to /thatpage. So whenever someone goes to /thispage, s/he will land on /thatpage.
If I use httplib/requests/urllib, will it know that there was a redirection? What error pages?
Some sites redirect user to /errorpage whenever the page cannot be found.
It depends on how they are doing the redirection. The "right" way is to return a redirected HTTP status code (301/302/303). The "wrong" way is to place a refresh meta tag in the HTML.
If they do the former, requests will handle it transparently. Note that any sane error page redirect will still have an error status code (e.g. 404) which you can check as response.status_code.
When I use python requests to check a site, if the site redirects me to another page, will I know?