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Python: BeautifulSoup库入门

Python入门 BeautifulSoup
2023-06-13 09:12:58 时间

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

<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

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

2 BeautifulSoup类的基本元素 

<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 
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
['\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']
len(soup.body.contents)
5
# 遍历儿子节点
for child in soup.body.children: 
    print(child)
# 遍历子孙节点
for child in soup.body.descendants: 
    print(child)
3.2 标签树的上行遍历
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
<head><title>This is a python demo page</title></head>
for parent in soup.a.parents:
    if parent is None:
        print(parent)
    else:
        print(parent.name)
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。 

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
' and '
soup.a.previous_sibling
'Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:\r\n'
# 遍历后续节点
for sibling in soup.a.next_siblings:
    print(sibling)
# 遍历前续节点
for sibling in soup.a.previous_siblings:
    print(sibling)

4 bs4库的prettify()方法

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()
'<html>\n <head>\n  <title>\n   This is a python demo page\n  </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 Python\n   </a>\n   and\n   <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">\n    Advanced Python\n   </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）

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