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🙏。

posted @ 2019-05-28 00:52 小菜技术阅读(301) 评论(0) 编辑收藏举报

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