第0009题：一个HTML文件，找出里面的链接。
在Beautiful Soup 4.2.0 文档里面有现成的例子。
html_doc = """
<html><head><title>The Dormouse's story</title></head>
<body>
<p class="title"><b>The Dormouse's story</b></p>
<p class="story">Once upon a time there were three little sisters; and their names were
<a href="http://example.com/elsie" class="sister" id="link1">Elsie</a>,
<a href="http://example.com/lacie" class="sister" id="link2">Lacie</a> and
<a href="http://example.com/tillie" class="sister" id="link3">Tillie</a>;
and they lived at the bottom of a well.</p>
<p class="story">...</p>
"""
from bs4 import BeautifulSoup
soup = BeautifulSoup(html_doc)
for link in soup.find_all('a'):
print(link.get('href'))
还有一个办法是HTMLParser库:
* handle_starttage(tag, attrs)
* handle_startendtage(tag, attrs)
* handle_endtage(tag)
* tag是html标签，
* attrs是(属性，值)元组的list
* HTMLParser自动将tag和attrs都转为小写
def handle_starttag(self, tag, attrs):
#print "Encountered the beginning of a %s tag" % tag
if tag == "a":
if len(attrs) == 0: pass
else:
for (variable, value) in attrs:
if variable == "href":
self.links.append(value)
