Python: BeautifulSoup库入门

文章背景：进行网络爬虫时，通过Requests模块获取网页的全部内容，借助BeautifulSoup模块从网页中提取内容。本文对BeautifulSoup模块的使用进行简单的介绍。

例子中用到的HTML页面地址：https://python123.io/ws/demo.html

代码语言：javascript复制

<html>
 <head>
  <title>
   This is a python demo page
  </title>
 </head>
 <body>
  <p class="title">
   <b>
    The demo python introduces several python courses.
   </b>
  </p>
  <p class="course">
   Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:
   <a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">
    Basic Python
   </a>
   and
   <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">
    Advanced Python
   </a>
   .
  </p>
 </body>
</html>

标签树：

BeautifulSoup库是解析、遍历、维护标签树的功能库。

1 BeautifulSoup库的解析器2 BeautifulSoup类的基本元素3 基于bs4库的HTML内容遍历方法3.1 标签树的下行遍历3.2 标签树的上行遍历3.3 标签树的平行遍历4 bs4库的prettify()方法

1 BeautifulSoup库的解析器

代码语言：javascript复制

soup = BeautifulSoup('<html>data</html>','html.parser')

2 BeautifulSoup类的基本元素

代码语言：javascript复制

<p class="title"> ... </p>

3 基于bs4库的HTML内容遍历方法

3.1 标签树的下行遍历

代码语言：javascript复制

from bs4 import BeautifulSoup
import requests
r = requests.get("https://python123.io/ws/demo.html")
demo = r.text
soup = BeautifulSoup(demo, 'html.parser')
soup.body.contents

代码语言：javascript复制

['n',
 <p class="title"><b>The demo python introduces several python courses.</b></p>,
 'n',
 <p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:
 <a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a> and <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>.</p>,
 'n']

代码语言：javascript复制

len(soup.body.contents)

代码语言：javascript复制

# 遍历儿子节点
for child in soup.body.children: 
    print(child)

代码语言：javascript复制

# 遍历子孙节点
for child in soup.body.descendants: 
    print(child)

3.2 标签树的上行遍历

代码语言：javascript复制

from bs4 import BeautifulSoup
import requests
r = requests.get("https://python123.io/ws/demo.html")
demo = r.text
soup = BeautifulSoup(demo, 'html.parser')
soup.title.parent

代码语言：javascript复制

<head><title>This is a python demo page</title></head>

代码语言：javascript复制

for parent in soup.a.parents:
    if parent is None:
        print(parent)
    else:
        print(parent.name)

代码语言：javascript复制

p
body
html
[document]

遍历所有先辈节点，包括soup本身。

3.3 标签树的平行遍历

平行遍历发生在同一个父节点下的各个节点之间。

代码语言：javascript复制

from bs4 import BeautifulSoup
import requests
r = requests.get("https://python123.io/ws/demo.html")
demo = r.text
soup = BeautifulSoup(demo, 'html.parser')
soup.a.next_sibling

代码语言：javascript复制

' and '

代码语言：javascript复制

soup.a.previous_sibling

代码语言：javascript复制

'Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:rn'

代码语言：javascript复制

# 遍历后续节点
for sibling in soup.a.next_siblings:
    print(sibling)

代码语言：javascript复制

# 遍历前续节点
for sibling in soup.a.previous_siblings:
    print(sibling)

4 bs4库的prettify()方法

代码语言：javascript复制

from bs4 import BeautifulSoup
import requests
r = requests.get("https://python123.io/ws/demo.html")
demo = r.text
soup = BeautifulSoup(demo, 'html.parser')
soup.prettify()

代码语言：javascript复制

'<html>n <head>n  <title>n   This is a python demo pagen  </title>n </head>n <body>n  <p class="title">n   <b>n    The demo python introduces several python courses.n   </b>n  </p>n  <p class="course">n   Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:n   <a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">n    Basic Pythonn   </a>n   andn   <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">n    Advanced Pythonn   </a>n   .n  </p>n </body>n</html>'

.prettify()方法为HTML文本<>及其内容增加'n'。

参考资料：

[1] 中国大学MOOC: Python网络爬虫与信息提取（https://www.icourse163.org/course/BIT-1001870001）

编程算法 html https 网络安全爬虫

0 人点赞