Python: 运用BeautifulSoup抓取网页的链接

程序实现的原理很简单，就是先把网页提取出来，再提取a标签，过滤出href。
方法1：

html = urllib2.urlopen(url).read()
#    html - unicode(html, 'gb2312', 'ignore').encode('utf-8', 'ignore')
content = BS(html).findAll('a')
    
myfile = open(localfile, 'w')
pat = re.compile(r'href="([^"]*)"')
pat2 = re.compile(r'http')
    
for item in content:
    h = pat.search(str(item))
    href = h.group(1)
    if pat2.search(href):
        ans = href
    else:
        ans = url + href

方法2：

 def extractlinks(html):
    soup = BS(html)
    anchors = soup.findAll('a')
    links = []
    for a in anchors:
        links.append(a['href'])
   return links

方法3：

base_url = "http://www.hao123.com"
html = urllib2.urlopen(base_url).read()
soup = BS(html)
urls = soup.findAll('a')
links = []
for url in urls:
    links.append(url["href"])

for i in range(len(links)):
    print links[i]