urljoin
from urlparse import urljoin
urljoin("http://www.asite.com/folder/currentpage.html", "anotherpage.html")
'http://www.asite.com/folder/anotherpage.html'
urljoin("http://www.asite.com/folder/currentpage.html", "folder2/anotherpage.html")
'http://www.asite.com/folder/folder2/anotherpage.html'
urljoin("http://www.asite.com/folder/currentpage.html", "/folder3/anotherpage.html")
'http://www.asite.com/folder3/anotherpage.html'
urljoin("http://www.asite.com/folder/currentpage.html", "../finalpage.html")
'http://www.asite.com/finalpage.html'
勤學如春起之苗,不見其增,日有所長。綴學如磨刀之石,不見其損,日有所虧。