python網(wǎng)絡爬蟲精解之Beautiful Soup的使用說明
一、Beautiful Soup的介紹
Beautiful Soup是一個強大的解析工具，它借助網(wǎng)頁結構和屬性等特性來解析網(wǎng)頁。
它提供一些函數(shù)來處理導航、搜索、修改分析樹等功能，Beautiful Soup不需要考慮文檔的編碼格式。Beautiful Soup在解析時實際上需要依賴解析器，常用的解析器是lxml。
二、Beautiful Soup的使用
test03.html測試實例：
<!DOCTYPE html>
<html>
<head>
<meta content="text/html;charset=utf-8" http-equiv="content-type" />
<meta content="IE=Edge" http-equiv="X-UA-Compatible" />
<meta content="always" name="referrer" />
<link rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="stylesheet" type="text/css" />
<title>百度一下，你就知道 </title>
</head>
<body link="#0000cc">
<div id="wrapper">
<div id="head">
<div class="head_wrapper">
<div id="u1">
<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trnews">新聞 </a>
<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trhao123">hao123 </a>
<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trmap">地圖 </a>
<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trvideo">視頻 </a>
<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trtieba">貼吧 </a>
<a class="bri" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_briicon" style="display: block;">更多產(chǎn)品 </a>
</div>
</div>
</div>
</div>
</body>
</html>
1、節(jié)點選擇器
我們之前了解到，一個網(wǎng)頁是由若干個元素節(jié)點組成的，通過提取某個節(jié)點的具體內容，就可以獲取到界面呈現(xiàn)的一些數(shù)據(jù)。使用節(jié)點選擇器能夠簡化我們獲取數(shù)據(jù)的過程，在不使用正則表達式的前提下，精準的獲取數(shù)據(jù)。
from bs4 import BeautifulSoup
file = open("./test03.html",'rb')
html = file.read()
soup = BeautifulSoup(html,'lxml')
print(soup.head)
print(soup.head.title)
print(soup.a)
【運行結果】
<head>
<meta content="text/html;charset=utf-8" http-equiv="content-type"/>
<meta content="IE=Edge" http-equiv="X-UA-Compatible"/>
<meta content="always" name="referrer"/>
<link rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="stylesheet" type="text/css"/>
<title>百度一下，你就知道 </title>
</head>
<title>百度一下，你就知道 </title>
<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trnews">新聞 </a>
分析：
第一條打印數(shù)據(jù)為獲取網(wǎng)頁的head節(jié)點；
第二條打印內容是獲取head節(jié)點中title節(jié)點，獲取該節(jié)點使用了一個嵌套選擇，因為title節(jié)點是嵌套在head節(jié)點里面的；
第三條打印內容是獲取a節(jié)點，在源碼中我們看到有許多條a節(jié)點，而只匹配到第一個a節(jié)點就結束了。當有多個節(jié)點時，這種選擇方式指只會選擇第一個匹配的節(jié)點，其他后面節(jié)點會忽略。
2、提取信息
一般我們需要的數(shù)據(jù)位于節(jié)點名、屬性值、文本值中，以下代碼展示了如何獲取這三個地方的數(shù)據(jù)：
from bs4 import BeautifulSoup
file = open("./test03.html",'rb')
html = file.read()
soup = BeautifulSoup(html,'lxml')
print(soup.body.name)
print(soup.body.a.attrs['class'])
print(soup.body.a.attrs['href'])
print(soup.body.a.string)
【運行結果】
body
['mnav']
http://news.baidu.com
新聞
分析：
第一條獲取body節(jié)點名；
第二條獲取a節(jié)點class屬性值；
第三條獲取a節(jié)點href屬性值；
第四條獲取a節(jié)點的文本值；
3、關聯(lián)選擇
（1）子節(jié)點和子孫節(jié)點
子節(jié)點可以調用contents屬性和children屬性，子孫節(jié)點可以調用descendants屬性，他們返回結果都是生成器類型，通過for循環(huán)輸出匹配到的信息。
from bs4 import BeautifulSoup
file = open("./test03.html",'rb')
html = file.read()
soup = BeautifulSoup(html,'lxml')
# print(soup.body.contents)
for i,content in enumerate(soup.body.contents):
print(i,content)
【運行結果】
0
1 <div id="wrapper">
<div id="head">
<div class="head_wrapper">
<div id="u1">
<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trnews">新聞 </a>
<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trhao123">hao123 </a>
<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trmap">地圖 </a>
<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trvideo">視頻 </a>
<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trtieba">貼吧 </a>
<a class="bri" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_briicon" style="display: block;">更多產(chǎn)品 </a>
</div>
</div>
</div>
</div>
2
（2）父節(jié)點和祖先節(jié)點
獲取某個節(jié)點的父節(jié)點可以調用parent屬性，例如獲取實例中title節(jié)點的父節(jié)點：
file = open("./test03.html",'rb')
html = file.read()
soup = BeautifulSoup(html,'lxml')
print(soup.title.parent)
【運行結果】
<head>
<meta content="text/html;charset=utf-8" http-equiv="content-type"/>
<meta content="IE=Edge" http-equiv="X-UA-Compatible"/>
<meta content="always" name="referrer"/>
<link rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="stylesheet" type="text/css"/>
<title>百度一下，你就知道 </title>
</head>
同理，如果是想要獲取節(jié)點的祖先節(jié)點，則可調用parents屬性。
（3）兄弟節(jié)點
調用next_sibling獲取節(jié)點的下一個兄弟元素；
調用previous_sibling獲取節(jié)點的上一個兄弟元素；
調用next_siblings取節(jié)點的下一個兄弟節(jié)點；
調用previous_siblings獲取節(jié)點的上一個兄弟節(jié)點；
4、方法選擇器
find_all（）
查找所有符合條件的元素，其使用方法如下：
find_all(name,attrs,recursive,text,**kwargs)
（1）name
根據(jù)節(jié)點名來查詢元素，例如查詢實例中a標簽元素：
from bs4 import BeautifulSoup
file = open("./test03.html",'rb')
html = file.read()
soup = BeautifulSoup(html,'lxml')
print(soup.find_all(name = "a"))
for a in soup.find_all(name = "a"):
print(a)
【運行結果】
[<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trnews">新聞 </a>, <a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trhao123">hao123 </a>, <a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trmap">地圖 </a>, <a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trvideo">視頻 </a>, <a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trtieba">貼吧 </a>, <a class="bri" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_briicon" style="display: block;">更多產(chǎn)品 </a>]
<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trnews">新聞 </a>
<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trhao123">hao123 </a>
<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trmap">地圖 </a>
<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trvideo">視頻 </a>
<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trtieba">貼吧 </a>
<a class="bri" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_briicon" style="display: block;">更多產(chǎn)品 </a>
（2）attrs
在查詢時我們還可以傳入標簽的屬性，attrs參數(shù)的數(shù)據(jù)類型是字典。
from bs4 import BeautifulSoup
file = open("./test03.html",'rb')
html = file.read()
soup = BeautifulSoup(html,'lxml')
print(soup.find_all(name = "a",attrs = {"class":"bri"}))
【運行結果】
[<a class="bri" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_briicon" style="display: block;">更多產(chǎn)品 </a>]
可以看到，在加上class=“bri”屬性時，查詢結果就只剩一條a標簽元素。
（3）text
text參數(shù)可以用來匹配節(jié)點的文本，傳入的可以是字符串，也可以是正則表達式對象。
import re
from bs4 import BeautifulSoup
file = open("./test03.html",'rb')
html = file.read()
soup = BeautifulSoup(html,'lxml')
print(soup.find_all(name = "a",text = re.compile('新聞')))
【運行結果】
[<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trnews">新聞 </a>]
只包含文本內容為“新聞”的a標簽。
find（）
find（）的使用與前者相似，唯一不同的是，find進匹配搜索到的第一個元素，然后返回單個元素，find_all（）則是匹配所有符合條件的元素，返回一個列表。
5、CSS選擇器
使用CSS選擇器時，調用select（）方法，傳入相應的CSS選擇器；
例如使用CSS選擇器獲取實例中的a標簽
from bs4 import BeautifulSoup
file = open("./test03.html",'rb')
html = file.read()
soup = BeautifulSoup(html,'lxml')
print(soup.select('a'))
for a in soup.select('a'):
print(a)
【運行結果】
[<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trnews">新聞 </a>, <a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trhao123">hao123 </a>, <a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trmap">地圖 </a>, <a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trvideo">視頻 </a>, <a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trtieba">貼吧 </a>, <a class="bri" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_briicon" style="display: block;">更多產(chǎn)品 </a>]
<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trnews">新聞 </a>
<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trhao123">hao123 </a>
<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trmap">地圖 </a>
<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trvideo">視頻 </a>
<a class="mnav" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_trtieba">貼吧 </a>
<a class="bri" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" name="tj_briicon" style="display: block;">更多產(chǎn)品 </a>
獲取屬性
獲取上述a標簽中的href屬性
from bs4 import BeautifulSoup
file = open("./test03.html",'rb')
html = file.read()
soup = BeautifulSoup(html,'lxml')
for a in soup.select('a'):
print(a['href'])
【運行結果】
http://news.baidu.com
https://www.hao123.com
http://map.baidu.com
http://v.baidu.com
http://tieba.baidu.com
//www.baidu.com/more/
獲取文本
獲取上述a標簽的文本內容，使用get_text()方法，或者是string獲取文本內容
from bs4 import BeautifulSoup
file = open("./test03.html",'rb')
html = file.read()
soup = BeautifulSoup(html,'lxml')
for a in soup.select('a'):
print(a.get_text())
print(a.string)
【運行結果】
新聞
新聞
hao123
hao123
地圖
地圖
視頻
視頻
貼吧
貼吧
更多產(chǎn)品
更多產(chǎn)品
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