python里的get_page函数

import urllib2
def get_page(url):
    return urllib2.urlopen(url).read()
 
def get_next_target(page):
    start_link = page.find('<a href=')
    if start_link == -1:
        return None, 0
    start_quote = page.find('"', start_link)
    end_quote = page.find('"', start_quote + 1)
    url = page[start_quote + 1:end_quote]
    return url, end_quote
 
def print_all_links(page):
    while True:
        url, endpos = get_next_target(page)
        if url:
            print url
            page = page[endpos:]
        else:
            break