python爬虫---从零开始（四）BeautifulSoup库
BeautifulSoup是什么？
BeautifulSoup是一个网页解析库，相比urllib、Requests要更加灵活和方便，处理高校，支持多种解析器。
利用它不用编写正则表达式即可方便地实现网页信息的提取。
BeautifulSoup的安装：直接输入pip3 install beautifulsoup4即可安装。4也就是它的最新版本。
BeautifulSoup的用法：
解析库：
| 解析器 | 使用方法 | 优势 | 不足 |
| Python标准库 | BeautifulSoup(markup,"html.parser") | python的内置标准库、执行速度适中、文档容错能力强 | Python2.7.3 or 3.2.2之前的版本容错能力较差 |
| lxml HTML解析库 | BeautifulSoup(markup,"lxml") | 速度快、文档容错能力强 | 需要安装C语言库 |
| lxml XML解析库 | BeautifulSoup(markup,"xml") | 速度快、唯一支持XML的解析器 | 需要安装C语言库 |
| html5lib | BeautifulSoup(markup,"html5lib") | 最好的容错性、以浏览器的方式解析文档、生成HTML5格式的文档 | 速度慢、不依赖外部扩展 |
基本使用：
html = """
<html><head><title>The Dormouse's story</head>
<body>
<p class="title" name="dromouse"><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/lacle" class="sister" id="link2">Lacie</a> and
<a href ="http://example.com/title" class="sister" id="link3">Title</a>; and they lived at the boottom of a well.</p>
<p class="story">...</p>
""" from bs4 import BeautifulSoup
soup = BeautifulSoup(html,'lxml')
print(soup.prettify())
print(soup.title.string)
我们可以看到，html这次参数是一段html代码，但是该代码并不完成，我们来看下下面的运行结果。
我们可以看到结果，BeautifulSoup将我们的代码自动补全了，并且帮我们自动格式化了html代码。
标签选择器：
选择元素
html = """
<html><head><title>The Dormouse's story</head>
<body>
<p class="title" name="dromouse"><b>The Dormouse's story</b></p>
<p class="story">Once upon a time there were three little sisters;and thier names were
<a href ="http://example.com/elsie" class="sister" id="link1"><!-- Elsie --></a>
<a href ="http://example.com/lacle" class="sister" id="link2">Lacie</a> and
<a href ="http://example.com/title" class="sister" id="link3">Title</a>; and they lived at the boottom of a well.</p>
<p class="story">...</p>
""" from bs4 import BeautifulSoup
soup = BeautifulSoup(html,'lxml')
print(soup.title)
print(type(soup.title))
print(soup.head)
print(soup.p)
我们先来看下运行结果
我们可以到看，.title方法将整个title标签全部提取出来了， .head也是如此的，但是p标签有很多，这里会默认只取第一个标签
获取名称 ：
#!/usr/bin/env python
# -*- coding: utf-8 -*- html = """
<html><head><title>The Dormouse's story</head>
<body>
<p class="title" name="dromouse"><b>The Dormouse's story</b></p>
<p class="story">Once upon a time there were three little sisters;and thier names were
<a href ="http://example.com/elsie" class="sister" id="link1"><!-- Elsie --></a>
<a href ="http://example.com/lacle" class="sister" id="link2">Lacie</a> and
<a href ="http://example.com/title" class="sister" id="link3">Title</a>; and they lived at the boottom of a well.</p>
<p class="story">...</p>
""" from bs4 import BeautifulSoup
soup = BeautifulSoup(html,'lxml')
print(soup.title.name)
输出结果为title 。.name方法获取该标签的名称（并非name属性的值）
获取属性：
#!/usr/bin/env python
# -*- coding: utf-8 -*- html = """
<html><head><title>The Dormouse's story</head>
<body>
<p class="title" name="dromouse"><b>The Dormouse's story</b></p>
<p class="story">Once upon a time there were three little sisters;and thier names were
<a href ="http://example.com/elsie" class="sister" id="link1"><!-- Elsie --></a>
<a href ="http://example.com/lacle" class="sister" id="link2">Lacie</a> and
<a href ="http://example.com/title" class="sister" id="link3">Title</a>; and they lived at the boottom of a well.</p>
<p class="story">...</p>
""" from bs4 import BeautifulSoup
soup = BeautifulSoup(html,'lxml')
print(soup.p.attrs['name'])
print(soup.p['name'])
我们尝试运行以后会发现，结果都为dromouse，也就是说两中方式都可以娶到name属性的值，但是只匹配第一个标签。
获取内容：
#!/usr/bin/env python
# -*- coding: utf-8 -*- html = """
<html><head><title>The Dormouse's story</head>
<body>
<p class="title" name="dromouse"><b>The Dormouse's story</b></p>
<p class="story">Once upon a time there were three little sisters;and thier names were
<a href ="http://example.com/elsie" class="sister" id="link1"><!-- Elsie --></a>
<a href ="http://example.com/lacle" class="sister" id="link2">Lacie</a> and
<a href ="http://example.com/title" class="sister" id="link3">Title</a>; and they lived at the boottom of a well.</p>
<p class="story" name="pname">...</p>
""" from bs4 import BeautifulSoup
soup = BeautifulSoup(html,'lxml')
print(soup.p.string)
输入标签.string方法即可取到该标签下的内容，得到的输出结果为：
我们可以看到我们获取到的是第一个p标签下的文字内容。
嵌套获取：
#!/usr/bin/env python
# -*- coding: utf-8 -*- html = """
<html><head><title>The Dormouse's story</head>
<body>
<p class="title" name="dromouse"><b>The Dormouse's story</b></p>
<p class="story">Once upon a time there were three little sisters;and thier names were
<a href ="http://example.com/elsie" class="sister" id="link1"><!-- Elsie --></a>
<a href ="http://example.com/lacle" class="sister" id="link2">Lacie</a> and
<a href ="http://example.com/title" class="sister" id="link3">Title</a>; and they lived at the boottom of a well.</p>
<p class="story" name="pname">...</p>
""" from bs4 import BeautifulSoup
soup = BeautifulSoup(html,'lxml')
print(soup.head.title.string)
运行结果为：
我们可以嵌套其子节点继续选择获取标签的内容。
获得子节点和子孙节点：
#!/usr/bin/env python
# -*- coding: utf-8 -*- html = """
<html><head><title>The Dormouse's story</head>
<body>
<p class="title" name="dromouse"><b>The Dormouse's story</b></p>
<p class="story">Once upon a time there were three little sisters;and thier names were
<a href ="http://example.com/elsie" class="sister" id="link1"><!-- Elsie --></a>
<a href ="http://example.com/lacle" class="sister" id="link2">Lacie</a> and
<a href ="http://example.com/title" class="sister" id="link3">Title</a>; and they lived at the boottom of a well.</p>
<p class="story" name="pname">...</p>
""" from bs4 import BeautifulSoup
soup = BeautifulSoup(html,'lxml')
print(soup.body.contents)
获取的结果为一个类型的数据，换行符也占用一个位置，我们来看一下输出结果：
另外还有一个方法也可以获得子节点.children也可以获取子节点：
#!/usr/bin/env python
# -*- coding: utf-8 -*- html = """
<html><head><title>The Dormouse's story</head>
<body>
<p class="title" name="dromouse"><b>The Dormouse's story</b></p>
<p class="story">Once upon a time there were three little sisters;and thier names were
<a href ="http://example.com/elsie" class="sister" id="link1"><!-- Elsie --></a>
<a href ="http://example.com/lacle" class="sister" id="link2">Lacie</a> and
<a href ="http://example.com/title" class="sister" id="link3">Title</a>; and they lived at the boottom of a well.</p>
<p class="story" name="pname">...</p>
""" from bs4 import BeautifulSoup
soup = BeautifulSoup(html,'lxml')
print(type(soup.body.children))
for i,child in enumerate(soup.body.children):
print(i,child)
输出结果如下：
用.children方法得到的是一个可以迭代的类型数据。
通过descendas可以获得其子孙节点：
#!/usr/bin/env python
# -*- coding: utf-8 -*- html = """
<html><head><title>The Dormouse's story</head>
<body>
<p class="title" name="dromouse"><b>The Dormouse's story</b></p>
<p class="story">Once upon a time there were three little sisters;and thier names were
<a href ="http://example.com/elsie" class="sister" id="link1"><!-- Elsie --></a>
<a href ="http://example.com/lacle" class="sister" id="link2">Lacie</a> and
<a href ="http://example.com/title" class="sister" id="link3">Title</a>; and they lived at the boottom of a well.</p>
<p class="story" name="pname">...</p>
""" from bs4 import BeautifulSoup
soup = BeautifulSoup(html,'lxml')
print(type(soup.body.descendants))
for i,child in enumerate(soup.body.descendants):
print(i,child)
我们来看一下运行结果：
获取父节点和祖先节点：
#!/usr/bin/env python
# -*- coding: utf-8 -*- html = """
<html>
<head>
<title>The Dormouse's story</title>
</head>
<body>
<p class="story" name="pname">Once upo a time were three little sister;and theru name were
<a href="http://example.com/elsie" class="sister" id="link1">
<span>Elsie</span>
</a>
<a href="http://example.com/elsie" class="sister" id="link2">Lacie</a>
and
<a href="http://example.com/elsie" class="sister" id="link3">Title</a>
</p>
<p class="story">...</p>
""" from bs4 import BeautifulSoup
soup = BeautifulSoup(html,'lxml')
print(type(soup.a.parent))
print(soup.a.parent)
我们来看一下运行结果：
获取其祖先节点：
#!/usr/bin/env python
# -*- coding: utf-8 -*- html = """
<html>
<head>
<title>The Dormouse's story</title>
</head>
<body>
<p class="story" name="pname">Once upo a time were three little sister;and theru name were
<a href="http://example.com/elsie" class="sister" id="link1">
<span>Elsie</span>
</a>
<a href="http://example.com/elsie" class="sister" id="link2">Lacie</a>
and
<a href="http://example.com/elsie" class="sister" id="link3">Title</a>
</p>
<p class="story">...</p>
""" from bs4 import BeautifulSoup as bs4
soup = bs4(html,'lxml')
print(type(soup.a.parents))
print(list(enumerate(soup.a.parents)))
我们来看下结果：
兄弟节点：
#!/usr/bin/env python
# -*- coding: utf-8 -*- html = """
<html>
<head>
<title>The Dormouse's story</title>
</head>
<body>
<p class="story" name="pname">Once upo a time were three little sister;and theru name were
<a href="http://example.com/elsie" class="sister" id="link1">
<span>Elsie</span>
</a>
<a href="http://example.com/elsie" class="sister" id="link2">Lacie</a>
and
<a href="http://example.com/elsie" class="sister" id="link3">Title</a>
</p>
<p class="story">...</p>
""" from bs4 import BeautifulSoup as bs4
soup = bs4(html,'lxml')
print(list(enumerate(soup.a.next_siblings)))
print(list(enumerate(soup.a.previous_siblings)))
我们来看一下结果：
next_siblings获得后面的兄弟节点，previous_siblings获得前面的兄弟节点。
以前就是我们用最简单的方式来获取了内容，也是标签选择器，选择速度很快的，但是这种选择器过于单一，不能满足我们的解析需求，下面我们来看一下标准选择器。
标准选择器：
find_all(name,attrs,recursive,text,**kwargs)可以根据标签名，属性，内容查找文档。
我们来看一下具体的用法。
根据name来查找：
#!/usr/bin/env python
# -*- coding: utf-8 -*- html = """
<html>
<head>
<title>The Dormouse's story</title>
</head>
<body>
<p class="story" name="pname">Once upo a time were three little sister;and theru name were
<a href="http://example.com/elsie" class="sister" id="link1">
<span>Elsie</span>
</a>
<a href="http://example.com/elsie" class="sister" id="link2">Lacie</a>
and
<a href="http://example.com/elsie" class="sister" id="link3">Title</a>
</p>
<p class="story">...</p>
""" from bs4 import BeautifulSoup as bs4
soup = bs4(html,'lxml')
print(soup.find_all('p'))
print(soup.find_all('p')[0])
我们看下结果：
我们通过find_all得到了一组数据，通过其索引得到每一项的标签。也可以用嵌套的方式来查找
attrs方式：
#!/usr/bin/env python
# -*- coding: utf-8 -*- html = """
<html>
<head>
<title>The Dormouse's story</title>
</head>
<body>
<p class="story" name="pname">Once upo a time were three little sister;and theru name were
<a href="http://example.com/elsie" class="sister" id="link1">
<span>Elsie</span>
</a>
<a href="http://example.com/elsie" class="sister" id="link2">Lacie</a>
and
<a href="http://example.com/elsie" class="sister" id="link3">Title</a>
</p>
<p class="story">...</p>
""" from bs4 import BeautifulSoup as bs4
soup = bs4(html,'lxml')
print(soup.find_all(attrs={'id':'link3'}))
print(soup.find_all(attrs={'class':'sister'}))
for i in soup.find_all(attrs={'class':'sister'}):
print(i)
运行结果：
我也可以这样来写：
#!/usr/bin/env python
# -*- coding: utf-8 -*- html = """
<html>
<head>
<title>The Dormouse's story</title>
</head>
<body>
<p class="story" name="pname">Once upo a time were three little sister;and theru name were
<a href="http://example.com/elsie" class="sister" id="link1">
<span>Elsie</span>
</a>
<a href="http://example.com/elsie" class="sister" id="link2">Lacie</a>
and
<a href="http://example.com/elsie" class="sister" id="link3">Title</a>
</p>
<p class="story">...</p>
""" from bs4 import BeautifulSoup as bs4
soup = bs4(html,'lxml')
print(soup.find_all(id='link3'))
print(soup.find_all(class_='sister'))
for i in soup.find_all(class_='sister'):
print(i)
对于特殊类型的我们可以直接用其属性来查找，例如id，class等。attrs更便于我们的查找了。
用text选择：
#!/usr/bin/env python
# -*- coding: utf-8 -*- html = """
<html>
<head>
<title>The Dormouse's story</title>
</head>
<body>
<p class="story" name="pname">Once upo a time were three little sister;and theru name were
<a href="http://example.com/elsie" class="sister" id="link1">
<span>Elsie</span>
</a>
<a href="http://example.com/elsie" class="sister" id="link2">Lacie</a>
and
<a href="http://example.com/elsie" class="sister" id="link3">Title</a>
<a href="http://example.com/elsie" class="body" id="link4">Title</a>
</p>
<p class="story">...</p>
""" from bs4 import BeautifulSoup as bs4
soup = bs4(html,'lxml')
print(soup.find_all(text='Title'))
运行结果：
find(name,attrs,recursive,text,**kwargs)可以根据标签名，属性，内容查找文档。和find_all用法完全一致，不同于find返回单个标签（第一个），find_all返回所有标签。
还有很多类似的方法：
#!/usr/bin/env python
# -*- coding: utf-8 -*- html = """
<html>
<head>
<title>The Dormouse's story</title>
</head>
<body>
<p class="story" name="pname">Once upo a time were three little sister;and theru name were
<a href="http://example.com/elsie" class="sister" id="link1">
<span>Elsie</span>
</a>
<a href="http://example.com/elsie" class="sister" id="link2">Lacie</a>
and
<a href="http://example.com/elsie" class="sister" id="link3">Title</a>
<a href="http://example.com/elsie" class="body" id="link4">Title</a>
</p>
<p class="story">...</p>
""" from bs4 import BeautifulSoup as bs4
soup = bs4(html,'lxml')
# find
print(soup.find(class_='sister'))
# find_parents() 和find_parent()
print(soup.find_parents(class_='sister')) # 返回祖先节点
print(soup.find_parent(class_='sister')) # 返回父节点
# find_next_siblings() ,find_next_sibling()
print(soup.find_next_siblings(class_='sister')) # 返回后面所有的兄弟节点
print(soup.find_next_sibling(class_='sister')) # 返回后面第一个兄弟节点
# find_previous_siblings() ,find_previous_sibling()
print(soup.find_previous_siblings(class_='sister')) # 返回前面所有的兄弟节点
print(soup.find_previous_sibling(class_='sister')) # 返回前面第一个兄弟节点
# find_all_next() ,find_next()
print(soup.find_all_next(class_='sister')) # 返回节点后所有符合条件的节点
print(soup.find_next(class_='sister')) # 返回节点后第一个满足条件的节点
# find_all_previous,find_all_previous
print(soup.find_all_previous(class_='sister')) # 返回节点后所有符合条件的节点
print(soup.find_all_previous(class_='sister')) # 返回节点后第一个满足条件的节点
在这里不在一一列举。
CSS选择器：通过select()直接传入CSS选择器即可完成选择
#!/usr/bin/env python
# -*- coding: utf-8 -*- html = """
<html>
<head>
<title>The Dormouse's story</title>
</head>
<body>
<p class="story" name="pname">Once upo a time were three little sister;and theru name were
<a href="http://example.com/elsie" class="sister" id="link1">
<span>Elsie</span>
</a>
<a href="http://example.com/elsie" class="sister" id="link2">Lacie</a>
and
<a href="http://example.com/elsie" class="sister" id="link3">Title</a>
<a href="http://example.com/elsie" class="body" id="link4">Title</a>
</p>
<p class="story">...</p>
""" from bs4 import BeautifulSoup as bs4
soup = bs4(html,'lxml')
print(soup.select('.body'))
print(soup.select('a'))
print(soup.select('#link3'))
我们select()的方法和jquery差不多的，选择class的前面加一个"." 选择id的前面加一个"#" 不加入任何的是标签选择器，我们来看下结果：
获取属性：
输入get_text()就可以获得到里面的文本了。
#!/usr/bin/env python
# -*- coding: utf-8 -*- html = """
<html>
<head>
<title>The Dormouse's story</title>
</head>
<body>
<p class="story" name="pname">Once upo a time were three little sister;and theru name were
<a href="http://example.com/elsie" class="sister" id="link1">
<span>Elsie</span>
</a>
<a href="http://example.com/elsie" class="sister" id="link2">Lacie</a>
and
<a href="http://example.com/elsie" class="sister" id="link3">Title</a>
<a href="http://example.com/elsie" class="body" id="link4">Title</a>
</p>
<p class="story">...</p>
""" from bs4 import BeautifulSoup as bs4
soup = bs4(html,'lxml')
for i in soup.select('.sister'):
print(i.get_text())
运行结果：
总结：
- 推荐使用lxml解析库，必要时使用html.parser库
- 标签选择筛选功能弱但是速度快
- 建议使用find()、find_all()查询匹配单个结果或者多个结果
- 如果对CSS选择器熟悉的建议使用select()
- 记住常用的获取属性和文本值的方法
代码地址：https://gitee.com/dwyui/BeautifulSoup.git
下一期我会来说一下pyQuery的使用，敬请期待。
感谢大家的阅读，不正确的地方，还希望大家来斧正，鞠躬，谢谢python爬虫---从零开始（四）BeautifulSoup库的更多相关文章
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