how to extract page-URL using BeautifulSoup

[bhaktanishant at gmail.com]

I want to extract the page-url. for example:
if i have this code

import urllib2
from bs4 import BeautifulSoup
link = "http://www.google.com"
page = urllib2.urlopen(link).read()
soup = BeautifulSoup(page)

then i can extract title of page by:

title = soup.title

but i want to know that how to extract page-URL from "soup" that will be "http://www.google.com"