BuautifulSoup4库详解

1、BeautifulSoup4库简介

What is beautifulsoup ?

答：一个可以用来从HTML 和 XML中提取数据的网页解析库，支持多种解析器（代替正则的复杂用法）

2、安装

pip3 install beautifulsoup4

3、用法详解

（1）、解析器性能分析（第一个参数markup-要解析的目标代码，第二个参数为解析器）

（2）、使用方法（独孤九剑）

1、总诀式：

#author: "xian"
#date: 2018/5/7
#以下为爱丽丝梦游仙境的部分代码
html = """
<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>
"""
#小试牛刀
from bs4 import BeautifulSoup #从bs4库导入BeautifulSoup类

soup = BeautifulSoup(html,'lxml') #构造名为soup的对象
print(soup.prettify()) #prettify修饰()方法：格式化代码也就是让各位小伙伴释放眼睛压力哈哈！
print(soup.a) #选中a标签
print(soup.a['class'])#打印a标签名为class的属性值
print(soup.a.name) #打印a 标签的名字 soup.a.parent.name 找到a标签的老子
print(soup.a.string) #小伙伴们猜猜看这是干什么？    答：打印a标签的文本
print(soup.find_all('a')) #找到所有的a标签
print(soup.find(id="link3"))#找到id属性值为link3的标签

#找链接
for link in soup.find_all('a'):
    print(link.get('href')) #遍历所有名为a的标签并得到其链接
#找文本
print(soup.a.get_text()) #获取a标签的文本当然小伙伴们可以任意指定想要的内容

#上面的输出
'''<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 class="sister" href="http://example.com/elsie" id="link1">
    Elsie
   </a>
   ,
   <a class="sister" href="http://example.com/lacie" id="link2">
    Lacie
   </a>
   and
   <a class="sister" href="http://example.com/tillie" id="link3">
    Tillie
   </a>
   ;
and they lived at the bottom of a well.
  </p>
  <p class="story">
   ...
  </p>
 </body>
</html>
<a class="sister" href="http://example.com/elsie" id="link1">Elsie</a>
['sister']
a
Elsie
[<a class="sister" href="http://example.com/elsie" id="link1">Elsie</a>, <a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>, <a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>]
<a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>
http://example.com/elsie
http://example.com/lacie
http://example.com/tillie'''

其他的小伙伴们可以根据需要获取想要的内容，掌握方法即可，具体可参见官网：https://www.crummy.com/software/BeautifulSoup/bs4/doc.zh/

2、破剑式

 1 #author: "xian"
 2 #date: 2018/5/7
 3 html = """
 4 <html>
 5     <head>
 6         <title>The Dormouse's story</title>
 7     </head>
 8     <body>
 9         <p class="story">
10             Once upon a time there were three little sisters; and their names were
11             <a href="http://example.com/elsie" class="sister" id="link1">
12                 <span>Elsie</span>
13             </a>
14             <a href="http://example.com/lacie" class="sister" id="link2">Lacie</a>
15             and
16             <a href="http://example.com/tillie" class="sister" id="link3">Tillie</a>
17             and they lived at the bottom of a well
18         </p>
19         <p class="story">...</p>
20 """
21 #子节点及子孙节点（老子节点与祖宗节点的选择）的选择
22 from bs4 import BeautifulSoup
23 
24 soup = BeautifulSoup(html,'lxml')
25 print(soup.p.contents) #contents方法将得到的结果以列表形式输出
26 print(soup.p.children) #是一个迭代器对象，需要用for循环才能得到器内容 children 只后期子节点
27 for i,child in enumerate(soup.p.children): #enumerate() 函数用于将一个可遍历的数据对象(如列表、元组或字符串)组合为一个索引序列，同时列出数据和数据下标，一般用在 for 循环当中。
28     print(i,child) #接受index 和内特
29 print(soup.p.descendants)  #descendants 获取所有的儿子和孙子后代节点
30 for i,child in enumerate(soup.p.descendants):
31     print(i,child)
32 
33 #上面的输出结果
34 '''['
            Once upon a time there were three little sisters; and their names were
            ', < a
35 class ="sister" href="http://example.com/elsie" id="link1" >
36 < span > Elsie < / span >
37 < / a >, '
', < a class ="sister" href="http://example.com/lacie" id="link2" > Lacie < / a >, '
            and
            ', < a class ="sister" href="http://example.com/tillie" id="link3" > Tillie < / a >, '
            and they lived at the bottom of a well
        ']
38 < list_iterator object at 0x00000156B2E76EF0 >
39 0
40             Once upon a time there were three little sisters; and their names were
41 
42 
43 1 < a class ="sister" href="http://example.com/elsie" id="link1" >
44 < span > Elsie < / span >
45 < / a >
46 2
47 
48 
49 3 < a class ="sister" href="http://example.com/lacie" id="link2" > Lacie < / a >
50 4
51             and
52 
53 
54 5 < a class ="sister" href="http://example.com/tillie" id="link3" > Tillie < / a >
55 6
56             and they lived at the bottom of a well
57 
58 
59 < generator object descendants at 0x00000156B08910F8 >
60 0
61 
62 Once upon a time there were three little sisters; and their names were
63 
64 
65 
66 1 < a class ="sister" href="http://example.com/elsie" id="link1" >
67 < span > Elsie < / span >
68 < /a >
69 2
70 
71 
72 3 < span > Elsie < / span >
73 4 Elsie
74 5
75 
76 
77 6
78 
79 
80 7 < a class ="sister" href="http://example.com/lacie" id="link2" > Lacie < / a >
81 8 Lacie
82 9
83             and
84 
85 
86 10 < a class ="sister" href="http://example.com/tillie" id="link3" > Tillie < / a >
87 11 Tillie
88 12
89         and they lived at the bottom of a well'''
90 
91 
92 #老子节点和祖宗节点方法介绍 children -- parent / descendants -- parents 小伙伴们模仿上面的可是动手试试
93 #兄弟节点的获取 方法为：next_siblings：获取当前对象后面的兄弟节点 previous_siblings:获取当前对象前面的兄弟节点，小伙伴们可以试试

3、破刀式

 1 #author: "xian"
 2 #date: 2018/5/7
 3 #搜索文档内容 find_all() 和find()
 4 html = """
 5 <html><head><title>The Dormouse's story</title></head>
 6 
 7 <p class="title"><b>The Dormouse's story</b></p>
 8 
 9 <p class="story">Once upon a time there were three little sisters; and their names were
10 <a href="http://example.com/elsie" class="sister" id="link1">Elsie</a>,
11 <a href="http://example.com/lacie" class="sister" id="link2">Lacie</a> and
12 <a href="http://example.com/tillie" class="sister" id="link3">Tillie</a>;
13 and they lived at the bottom of a well.</p>
14 
15 <p class="story">...</p>
16 """
17 from bs4 import BeautifulSoup
18 import re
19 
20 soup = BeautifulSoup(html,'lxml')
21 #(1)、find_all( name , attrs , recursive , text , **kwargs )
22 #name参数用法详解（text参数的使用同name类似如soup.find_all(text=["Tillie", "Elsie", "Lacie"])只返回内容，小伙伴们可查阅官方文档：https://www.crummy.com/software/BeautifulSoup/bs4/doc.zh/）
23 print(soup.find_all('head')) #查找head标签
24 print(soup.find_all(id='link2')) #查找id='link2'的标签
25 print(soup.find_all(href=re.compile("(w+)"))) #查找所有包含href属性包含字母数字的标签
26 print(soup.find_all(href=re.compile("(w+)"), id='link1')) #多重过滤
27 #搜索指定名字的属性时可以使用的参数值包括 字符串 , 正则表达式 , 列表, True
28 
29 #attrs参数用法详解
30 print(soup.find_all(attrs={'id':'link2'})) #attrs参数以key-value形式传入值 /返回列表类型
31 
32 #（2）find( name , attrs , recursive , text , **kwargs )用法同find_all 类似只不过它只返回一个值，小伙伴们可以查找官方用法
33 
34 #（3）其他方法汇总：(小伙伴们了解即可具体碰到查文档)
35 #find_parents() 和find_parent() 返回祖宗节点 和 返回老子节点
36 #find_next_siblings() 和 find_next_sibling() 返回后面所有的兄弟节点 和 返回后面第一个兄弟节点
37 #find_previous_siblings() 和 find_previous_sibling() 返回前面所有的兄弟节点 和 返回前面第一个兄弟节点
38 #find_all_next() 和 find_next() 返回节点后满足条件所有的节点 和 返回第一个满足条件的节点
39 #find_all_previous() 和 find_previous() 返回节点前满足条件所有的节点 和 返回第一个满足条件的节点
40 
41 #上面的输出结果：
42 '''
43 [<head><title>The Dormouse's story</title></head>]
44 [<a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>]
45 [<a class="sister" href="http://example.com/elsie" id="link1">Elsie</a>, <a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>, <a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>]
46 [<a class="sister" href="http://example.com/elsie" id="link1">Elsie</a>]
47 [<a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>]
48 <class 'bs4.element.ResultSet'>
49 '''

4、破枪式

 1 #author: "xian"
 2 #date: 2018/5/7
 3 #CSS选择器详解（通过select()传入css选择器即可成功选择）
 4 html = """
 5 <html><head><title>The Dormouse's story</title></head>
 6 <body>
 7 <p class="title"><b>The Dormouse's story</b></p>
 8 
 9 <p class="story">Once upon a time there were three little sisters; and their names were
10 <a href="http://example.com/elsie" class="sister" id="link1">Elsie</a>,
11 <a href="http://example.com/lacie" class="sister" id="link2">Lacie</a> and
12 <a href="http://example.com/tillie" class="sister" id="link3">Tillie</a>;
13 and they lived at the bottom of a well.</p>
14 
15 <p class="story">...</p>
16 """
17 from bs4 import BeautifulSoup
18 
19 soup = BeautifulSoup(html,'lxml')
20 print(soup.select('.title')) #选择class属性为title的标签 css选择器使用请小伙伴们查看官网
21 #再来一例
22 print(soup.select('p a#link1'))# 选择p标签下的a下的id属性为link1的标签
23 print(soup.select('a')[1]) #做一个切片拿到第二个a标签
24 #获取内容
25 print(soup.select('a')[1].get_text()) 
26 
27 #上面的输出：
28 '''
29 [<p class="title"><b>The Dormouse's story</b></p>]
30 [<a class="sister" href="http://example.com/elsie" id="link1">Elsie</a>]
31 <a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>
32 laci
33 '''

通过以上的实验，小伙伴们对bs4库是否有了一定的了解，赶紧行动起来，试试学习的效果吧！

总结：

1.建议小伙伴使用lxml解析器

2.多用find_all()和find()

3.css的select()方法掌握下

4.多练习，勤能补拙，孰能生巧，才能渐入化境！