get data in web

import urllib
u = urllib.urlopen('http://learnprobyjack.pe.hu/')
data = u.read()
def urlfinder(html,string):
    #condition
    i = 0
    if html.find(string) == -1:
        print 'Web site khong co muc "' + string + 'nay'
        return 0
    if (html.find(string) != -1) or (html.find(string) != 0):
        while i >= 0:
            if html[html.find(string)+len(string)+i] == '<' and html[html.find(string)+len(string)+i+1] == '/':
                return html[html.find(string)+len(string)+1:html.find(string)+len(string)+i]
                break
            i = i + 1
print urlfinder(data,'number')