python 如何获取页面所有a标签下href的值

# -*- coding:utf-8 -*-
#python 2.7
#http://tieba.baidu.com/p/2460150866
#标签操作 
 
from bs4 import BeautifulSoup
import urllib.request
import re 
 
#如果是网址，可以用这个办法来读取网页
#html_doc = "http://tieba.baidu.com/p/2460150866"
#req = urllib.request.Request(html_doc)  
#webpage = urllib.request.urlopen(req)  
#html = webpage.read() 
 
html="""
html>head>title>The Dormouse's story/title>/head>
body>
p class="title" name="dromouse">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" rel="external nofollow"  rel="external nofollow"  class="sister" id="xiaodeng">!-- Elsie -->/a>,
a href="http://example.com/lacie" rel="external nofollow"  rel="external nofollow"  class="sister" id="link2">Lacie/a> and
a href="http://example.com/tillie" rel="external nofollow"  class="sister" id="link3">Tillie/a>;
a href="http://example.com/lacie" rel="external nofollow"  rel="external nofollow"  class="sister" id="xiaodeng">Lacie/a>
and they lived at the bottom of a well./p>
p class="story">.../p>
"""
soup = BeautifulSoup(html, 'html.parser')   #文档对象 
 
#查找a标签,只会查找出一个a标签
#print(soup.a)#a class="sister" href="http://example.com/elsie" rel="external nofollow"  rel="external nofollow"  id="xiaodeng">!-- Elsie -->/a>
 
for k in soup.find_all('a'):
    print(k)
    print(k['class'])#查a标签的class属性
    print(k['id'])#查a标签的id值
    print(k['href'])#查a标签的href值
    print(k.string)#查a标签的string 
    

soup = BeautifulSoup(html, 'html.parser')   #文档对象
#查找a标签,只会查找出一个a标签
for k in soup.find_all('a'):
    print(k)
    print(k['class'])#查a标签的class属性
    print(k['id'])#查a标签的id值
    print(k['href'])#查a标签的href值
    print(k.string)#查a标签的string

 html = urlopen(url)
 soup = BeautifulSoup(html, 'html.parser')
 t1 = soup.find_all('a')
 print t1
 href_list = []
 for t2 in t1:
    t3 = t2.get('href')
    href_list.append(t3)

# coding=utf-8 
from bs4 import BeautifulSoup 
import requests 
# 定义一个获取url页面下label标签的attr属性的函数 
def getHtml(url, label, attr): 
    response = requests.get(url) 
    response.encoding = 'utf-8' 
    html = response.text 
    soup = BeautifulSoup(html, 'html.parser'); 
    for target in soup.find_all(label):
 
        try: 
            value = target.get(attr)
 
        except: 
            value = ''
 
        if value: 
            print(value)
 
url = 'https://baidu.com/' 
label = 'a' 
attr = 'href' 
getHtml(url, label, attr)