I think the answer is that when we take a link from here 'http://www.python.org/ for example , it looks like this <a href="/about/>about</a>.
So if i take the href part which is /about/ here and use urljoin to join this string (of course with .html) to the main url which is 'http://python.org/' here. Correct?!
Of course i should delete those / and / from /about/ first.