BeautifulSoup基本用法

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cnhkzyy 2022-07-04 20:10:05 博主文章分类：爬虫 ©著作权

文章标签 html xml 父节点 文章分类 Html/CSS 前端开发

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BeautifulSoup是Python的一个HTML或XML的解析库，可以用它来方便地从网页提取数据（以下为崔庆才的爬虫书的学习笔记）

一. 安装方式

#安装beautifulsoup4
pip install beautifulsoup4

#安装lxml
pip install lxml

二. 基本语法

1. 节点选择器：基本用法

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 are 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>
"""

假如想要获取上述html中的title节点及其文本内容，请看以下语法：

引入并初始化beautifulsoup

from bs4 import BeautifulSoup

soup = BeautifulSoup(html, 'lxml')

初始化对于一些不标准的html，可以自动更正格式，如补全标签等等

获取title节点，查看它的类型

print(soup.title)
print(type(soup.title))


#输出结果
<title>The Dormouse's story</title>
<class 'bs4.element.Tag'>

获取到的title节点，正是节点加文本内容

获取title节点文本内容

print(soup.title.string)


#输出结果
The Dormouse's story

如果想获取其他信息，比如节点的名字及其属性，这些也比较方便

获取title节点的名字

print(soup.title.name)


#输出结果
title

获取p节点的多个属性和某一属性

p节点有多个属性，比如class和name等，可以调用attrs获取所有属性

#获取多个属性
print(soup.p.attrs)

#输出结果：
{'class': ['title'], 'name': 'dromouse'}


#获取某个属性：方法一
print(soup.p.attrs['name']

#输出结果：
dromouse


#获取某个属性：方法二
print(soup.p['name']

#输出结果：
dromouse


#获取单个属性需要注意的地方
print(soup.p['class'])

#输出结果：
['title']

需要注意的是，有的返回的是字符串，有的返回的是字符串组成的列表。比如，name属性的值是唯一的，返回的结果就是单个字符串，而对于class，一个节点的元素可能有多个class，所以返回的是列表。另外，这里的p节点是第一个p节点

嵌套选择或层级选择

如果多个节点层级嵌套在一起，可以通过层级关系依次选择，比如要选择title节点及其内容，之前我们是soup.title，现在可以这样操作：soup.head.title

html = """
<html><head><title>The Dormouse's story</title></head>
<body>
"""

print(soup.head.title)
print(type(soup.head.title))
print(soup.head.title.string)


#输出结果：
<title>The Dormouse's story</title>
<class 'bs4.element.Tag'>
The Dormouse's story

2. 节点选择器：高级用法

父节点和祖先节点

如果要获取某个节点元素的父节点，可以调用parent属性

html = """
<html>
<head>
<title>The Dormouse's story</title>
</head>
<body>
<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">
<span>Elsie</span>
</a>
</p>
<p class="story>...</p>
"""

from bs4 import BeautifulSoup

soup = BeautifulSoup(html, 'lxml')
print(soup.a.parent)


#输出结果：

<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">
<span>Elsie</span>
</a>
</p>

这里我们选择的是第一个a节点的父节点元素，很明显，它的父节点是p节点，输出结果便是p节点及其内部的内容

如果想要获取所有的祖先元素，可以调用parents属性：

html = """
<html>
<body>
<p class="story">
<a href="http://example.com/elsie" class="sister" id="link1">
<span>Elsie</span>
</a>
</p>
"""

from bs4 import BeautifulSoup
soup = BeautifulSoup(html, 'lxml')
print(type(soup.a.parents))
print(list(enumerate(soup.a.parents)))


#运行结果：
<class 'generator'>
[(0, <p class="story">
<a class="sister" href="http://example.com/elsie" id="link1">
<span>Elsie</span>
</a>
</p>), (1, <body>
<p class="story">
<a class="sister" href="http://example.com/elsie" id="link1">
<span>Elsie</span>
</a>
</p>
</body>), (2, <html>
<body>
<p class="story">
<a class="sister" href="http://example.com/elsie" id="link1">
<span>Elsie</span>
</a>
</p>
</body></html>), (3, <html>
<body>
<p class="story">
<a class="sister" href="http://example.com/elsie" id="link1">
<span>Elsie</span>
</a>
</p>
</body></html>)]

这里为什么出现了两个html开头的文本呢？是因为parents遍历的顺序是p—body—html—[document]

子节点和子孙节点

选取节点元素知乎，如果想要获取它的直接子节点，可以调用contents属性：

html = """
<html>
<head>
<title>The Dormouse's story</title>
</head>
<body>
<p class="story">
    Once upon a time there were three little sisters; and their names were
    <a href="http://example.com/elise" class="sister" id="link1">
<span>Elise</span>
</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>
"""

可以看到，返回结果是列表形式。p节点里既包含文本，又包含节点

from bs4 import BeautifulSoup
soup = BeautifulSoup(html, 'lxml')
print(soup.p.contents)


#运行结果：
['\n    Once upon a time there were three little sisters; and their names were\n    ', <a class="sister" href="http://example.com/elise" id="link1">
<span>Elise</span>
</a>, '\n', <a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>, '\nand\n', <a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>, '\nand they lived at the bottom of a well.\n']

span节点作为p节点的孙子节点，并没有单独列出，而是包含在a中被列出，说明contents属性得到的结果是直接子节点的列表

同样，我们可以调用children属性得到相应的结果：

from bs4 import BeautifulSoup
soup = BeautifulSoup(html, 'lxml')
print(soup.p.children)
for i, child in enumerate(soup.p.children):
    print(i, child)


#运行结果：
<list_iterator object at 0x000000000303F7B8>
0 
    Once upon a time there were three little sisters; and their names were
    
1 <a class="sister" href="http://example.com/elise" id="link1">
<span>Elise</span>
</a>
2 

3 <a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>
4 
and

5 <a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>
6 
and they lived at the bottom of a well.

如果还想获得所有的子孙节点的话，可以调用descendants属性：

from bs4 import BeautifulSoup
soup = BeautifulSoup(html, 'lxml')
print(soup.p.descendants)
for i, child in enumerate(soup.p.descendants):
    print(i, child)


#运行结果：
<generator object Tag.descendants at 0x000000000301F228>
0 
    Once upon a time there were three little sisters; and their names were
    
1 <a class="sister" href="http://example.com/elise" id="link1">
<span>Elise</span>
</a>
2 

3 <span>Elise</span>
4 Elise
5 

6 

7 <a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>
8 Lacie
9 
and

10 <a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>
11 Tillie
12 
and they lived at the bottom of a well.

遍历输出可以看到，这次输出的结果就包含了span节点，descendants会递归查询所有子节点，得到所有的子孙节点

兄弟节点

如果想获取兄弟节点，应该怎么办呢？

html = """
<html>
<body>
<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">
<span>Elsie</span>
</a>
            Hello
<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>
"""

from bs4 import BeautifulSoup
soup = BeautifulSoup(html, 'lxml')
print('Next Sibling', soup.a.next_sibling)
print('Prev Sibling', soup.a.previous_sibling)
print('Next Siblings', list(enumerate(soup.a.next_siblings)))
print('Prev Siblings', list(enumerate(soup.a.previous_siblings)))


#输出结果：
Next Sibling 
            Hello

Prev Sibling 
            Once upon a time there were three little sisters; and their names were

Next Siblings [(0, '\n            Hello\n'), (1, <a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>), (2, '\n            and\n'), (3, <a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>), (4, '\n            and they lived at the bottom of a well.\n')]
Prev Siblings [(0, '\n            Once upon a time there were three little sisters; and their names were\n')]

next_sibling和previous_sibling分别获取节点的下一个和上一个兄弟元素，next_siblings和previous_siblings则分别返回后面和前面的兄弟节点

3. 方法选择器

find_all()：查询所有符合条件的元素

html = '''
<div class="panel">
<div class="panel-heading">
<h4>Hello</h4>
</div>
<div class="panel-body">
<ul class="list" id="list-1">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>
<ul class="list list-small" id="list-2">
<li class="element">Foo</li>
<li class="element">Bar</li>
</ul>
</div>
</div>
'''

from bs4 import BeautifulSoup
soup = BeautifulSoup(html, 'lxml')
print(soup.find_all(name='ul'))
print(type(soup.find_all(name='ul')[0]))



#运行结果：
[<ul class="list" id="list-1">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>, <ul class="list list-small" id="list-2">
<li class="element">Foo</li>
<li class="element">Bar</li>
</ul>]
<class 'bs4.element.Tag'>

利用find_all方法查询ul节点，返回结果是列表类型，长度为2，每个元素都是bs4.element.Tag类型

还可以进行嵌套查询，获取li节点的文本内容

for ul in soup.find_all(name='ul'):
    print(ul.find_all(name='li'))
    for li in ul.find_all(name='li'):
        print(li.string)


#输出结果：
[<li class="element">Foo</li>, <li class="element">Bar</li>, <li class="element">Jay</li>]
Foo
Bar
Jay
[<li class="element">Foo</li>, <li class="element">Bar</li>]
Foo
Bar

除了根据节点名查询，还可以传入一些属性来查询

html = '''
<div class="panel">
<div class="panel-heading">
<h4>Hello</h4>
</div>
<div class="panel-body">
<ul class="list" id="list-1" name="elements">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>
<ul class="list list-small" id="list-2">
<li class="element">Foo</li>
<li class="element">Bar</li>
</ul>
</div>
</div>
'''

from bs4 import BeautifulSoup
soup = BeautifulSoup(html, 'lxml')
print(soup.find_all(attrs={'id': 'list-1'}))
print(soup.find_all(attrs={'name': 'elements'}))


#输出结果：
[<ul class="list" id="list-1" name="elements">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>]
[<ul class="list" id="list-1" name="elements">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>]

对于一些常用的属性，比如id和class等，可以不用attrs来传递。比如，要查询id为list-1的节点，可以直接传入id这个参数。还是上面的文本，我们换一种方式来查询：

from bs4 import BeautifulSoup
soup = BeautifulSoup(html, 'lxml')
print(soup.find_all(id='list-1'))
print(soup.find_all(class_='element'))


#输出结果：
[<ul class="list" id="list-1" name="elements">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>]
[<li class="element">Foo</li>, <li class="element">Bar</li>, <li class="element">Jay</li>, <li class="element">Foo</li>, <li class="element">Bar</li>]

text参数可以用来匹配节点的文本，传入的形式可以是字符串，可以是正则表达式对象

html = '''
<div class="panel">
<div class="panel-body">
<a>Hello, this is a link</a>
<a>Hello, this is a link, too</a>
</div>
</div>
'''

from bs4 import BeautifulSoup
import re

soup = BeautifulSoup(html, 'lxml')
print(soup.find_all(text=re.compile('link')))


#输出结果：
['Hello, this is a link', 'Hello, this is a link, too']

find()：返回单个元素，也就是第一个匹配的元素

html = '''
<div class="panel">
<div class="panel-heading">
<h4>Hello</h4>
</div>
<div class="panel-body">
<ul class="list" id="list-1">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>
<ul class="list list-small" id="list-2">
<li class="element">Foo</li>
<li class="element">Bar</li>
</ul>
</div>
</div>
'''

from bs4 import BeautifulSoup
soup = BeautifulSoup(html, 'lxml')
print(soup.find(name='ul'))
print(type(soup.find(name='ul')))
print(soup.find(class_='list'))


#输出结果：
<ul class="list" id="list-1">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>
<class 'bs4.element.Tag'>
<ul class="list" id="list-1">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>

其他的查询方法

find_parents()和find_parent()：前者返回所有祖先节点，后者返回直接父节点

find_next_siblings()和find_next_sibling()：前者返回后面所有的兄弟节点，后者返回后面第一个兄弟节点

find_previous_siblings()和find_previous_sibling()：前者返回前面所有的兄弟节点，后者返回前面第一个兄弟节点

find_all_next()和find_next()：前者返回节点后所有符合条件的节点，后者返回第一个符合条件的节点

find_all_previous()和find_previous()：前者返回节点前所有符合条件的节点，后者返回第一个符合条件的节点

3. CSS选择器

使用CSS选择器时，只需要调用select()方法，传入相应的CSS选择器即可

html = '''
<div class="panel">
<div class="panel-heading">
<h4>Hello</h4>
</div>
<div class="panel-body">
<ul class="list" id="list-1">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>
<ul class="list list-small" id="list-2">
<li class="element">Foo</li>
<li class="element">Bar</li>
</ul>
</div>
</div>
'''

from bs4 import BeautifulSoup
soup = BeautifulSoup(html, 'lxml')
print(soup.select('.panel .panel-heading'))
print(soup.select('ul li'))
print(soup.select('#list-2 .element'))
print(type(soup.select('ul')[0]))


#输出结果：
[<div class="panel-heading">
<h4>Hello</h4>
</div>]
[<li class="element">Foo</li>, <li class="element">Bar</li>, <li class="element">Jay</li>, <li class="element">Foo</li>, <li class="element">Bar</li>]
[<li class="element">Foo</li>, <li class="element">Bar</li>]
<class 'bs4.element.Tag'>

嵌套选择

select()方法同样支持嵌套选择。例如，先选择所有ul节点，再遍历每个ul节点

from bs4 import BeautifulSoup
soup = BeautifulSoup(html, 'lxml')
for ul in soup.select('ul'):
    print(ul.select('li'))


#输出结果：
[<li class="element">Foo</li>, <li class="element">Bar</li>, <li class="element">Jay</li>]
[<li class="element">Foo</li>, <li class="element">Bar</li>]

可以看到，这里正常输出了所有ul节点下所有li节点组成的列表

获取属性

from bs4 import BeautifulSoup
soup = BeautifulSoup(html, 'lxml')
for ul in soup.select('ul'):
    print(ul['id'])
    print(ul.attrs['id'])


#输出结果：
list-1
list-1
list-2
list-2

可以看到，直接传入中括号和属性名，或通过attrs属性获取属性值，都可以成功

获取文本

要获取文本，可以用前面所讲的string属性或者get_text()方法

from bs4 import BeautifulSoup
soup = BeautifulSoup(html, 'lxml')
for li in soup.select('li'):
    print('Get Text:', li.get_text())
    print('String:', li.string)


#输出结果：
Get Text: Foo
String: Foo
Get Text: Bar
String: Bar
Get Text: Jay
String: Jay
Get Text: Foo
String: Foo
Get Text: Bar
String: Bar