（1）和lxml一样,Beautifu Soup也是一个HTML/XML的解析器,主要的功能也是如何解析和提取HTML/XML数据。
（2）lxml只会局部遍历，而Beautiful Soup是基于HTML DOM的，会载入整个文档，解析整个DOM树，因此时间和内存开销都会大很多，所以性能要低于lxml。
（3）BeautifulSoup用来解析HTML比较简单，API非常人性化，支持CSS选择器、python标准库中的HTML解析器，也支持lxml的XML解析器。
安装：`pip install beautifusoup4`
官方文档：https://beautifulsoup.readthedocs.io/zh_CN/v4.4.0/
| 抓取工具 | 速度 | 使用难度 | 安装难度 |
|---|---|---|---|
| 正则 | 最快 | 困难 | 无（内置） |
| BeautifulSoup | 慢 | 最简单 | 简单 |
| lxml | 快 | 简单 | 一般 |
from bs4 import BeautifulSouphtml = """ <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 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/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>"""# 创建Beautiful Soup对象soup = BeautifulSoup(html,‘lxml‘)# 打开本地HTML文件的方式来创建对象# soup = BeautifulSoup(open(‘index.html‘))# 格式化输出soup对象的内容print(soup.prettify())
运行结果：
<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 were three little sisters; and their names were <a class="sister" href="http://example.com/elsie" id="link1"> <!-- Elsie --> </a> , <a class="sister" href="http://example.com/lacie" id="link2"> Lacie </a> and <a class="sister" href="http://example.com/tillie" id="link3"> Tillie </a> ;and they lived at the bottom of a well. </p> <p class="story"> ... </p> </body></html>
如果没有显示地指定解析器，会默认使用这个系统的最佳可用HTML解析器（‘lxml‘）。当在另一个系统中运行这段代码，或者在不同的虚拟环境中，使用不同的解析器会造成不同行为。
可以通过`soup=BeautifuSoup(html,‘lxml‘)`方式指定lxml解析器。
Beautifu Soup将复杂HTML文档转换成一个复杂的树形结构，每个节点都是python对象，所有对象可以归纳为4种：（1）Tag（2）NavigableString（3）BeautifulSoup（4）Comment
<head><title>The Dormouse‘s story</title></head><a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a><p class="title" name="dromouse"><b>The Dormouse‘s story</b></p>
Tag是，HTML中的一个个标签（即上面代码中的`title`、`head`、`a`、`p`等等HTML标签）加上里面包括的内容。
from bs4 import BeautifulSouphtml = """ <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 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/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>"""# 创建Beautiful Soup对象soup = BeautifulSoup(html,‘lxml‘)# 打开本地HTML文件的方式来创建对象# soup = BeautifulSoup(open(‘index.html‘))# 格式化输出soup对象的内容# print(soup.prettify())print(soup.title)# <title>The Dormouse‘s story</title>print(soup.head)# <head><title>The Dormouse‘s story</title></head>print(soup.a)# <a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>print(type(soup.a))# <class ‘bs4.element.Tag‘>
# 通过soup加标签名获取这些标签的内容，这些对象的类型是bs4.element.Tag
# 通过这种方法查找的是在所有内容中的第一个符合要求的标签。
# 对于Tag，它本身有两个重要的属性，即name和attrs
print(soup.name)# [document] # soup对象本身比较特殊，它的name即为[document]print(soup.head.name)# head# 对于其他内部标签，输出的值便为标签本身的名称print(soup.p.attrs)# {‘class‘: [‘title‘], ‘name‘: ‘dromouse‘}# 在这里，我们把p标签的所有属性打印了出来，得到的类型是一个字典print(soup.p[‘class‘])# [‘title’] 获取属性的值# 等同下列get方法print(soup.p.get(‘class‘))# [‘title‘] 获取属性的值soup.p[‘class‘] = ‘newClass‘
# 对p标签下的class属性的内容进行修改print(soup.p)# <p class="newClass" name="dromouse"><b>The Dormouse‘s story</b></p>
del soup.p[‘class‘] # 还可以对这个属性进行删除 print soup.p # <p name="dromouse"><b>The Dormouse‘s story</b></p>通过.string的方式即可获取标签内部的文字
print soup.p.string# The Dormouse‘s storyprint type(soup.p.string)# In [13]: <class ‘bs4.element.NavigableString‘>
BeautifulSoup对象表示的是一个文档的内容，可以把它当做是一个特殊的Tag对象，可以分别获取它的类型，名称以及属性。
print(type(soup.name))# <class ‘str‘>print(soup.name)# [document]print(soup.attrs)# {} 文档本身的属性为空
Comment对象是一个特殊类型的NavigableString对象，其输出的内容不包括注释符号。
print(soup.a)# <a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>print(soup.a.string)# Elsieprint(type(soup.a.string))# <class ‘bs4.element.Comment‘>
注意Comment和NavigableString对象的区别，当HTML标签的.string中有注释时，忽视注释符号，返回其中的内容，这时它是一个Comment对象；当没有注释时，返回其中的内容，这时它是一个NavigableString对象。
Tag的`.contents`属性可以将Tag的子节点以列表的方式输出
print(soup.body.contents)# tag的.contents属性可以将tag的子节点以列表的方式输出"""[‘\n‘, <p class="title" name="dromouse"><b>The Dormouse‘s story</b></p>, ‘\n‘, <p class="story">Once upon a time there were three little sisters; and their names were<a class = "sister" href = "http://example.com/elsie" id = "link1" > <!-- Elsie - -> < /a > ,<a class = "sister" href = "http://example.com/lacie" id = "link2" > Lacie < /a > and<a class = "sister" href = "http://example.com/tillie" id = "link3" > Tillie < /a >;and they lived at the bottom of a well. < /p > , ‘\n‘, < p class = "story" > ... < /p > , ‘\n‘]"""# 输出方式为列表，可以用列表索引来获取它的某一个元素print(soup.body.contents[1])#<p class="title" name="dromouse"><b>The Dormouse‘s story</b></p>
Tag的`.children`属性，返回一个list生成器对象。
print(soup.body.children)# <list_iterator object at 0x7f55adea9d68>for child in soup.body.children: print(child)
# 输出结果"""<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 class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>,<a class="sister" href="http://example.com/lacie" id="link2">Lacie</a> and<a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>;and they lived at the bottom of a well.</p><p class="story">...</p>"""
`.contents`和`.children`属性仅包含Tag的直接子节点，`.descendants`属性可以对所有Tag的子孙节点进行递归循环，和`.children`类似，返回一个生成器对象。
print(soup.descendants)# <generator object descendants at 0x7f98e70050f8>for child in soup.descendants: print(child)"""<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 were three little sisters; and their names were<a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>,<a class="sister" href="http://example.com/lacie" id="link2">Lacie</a> and<a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>;and they lived at the bottom of a well.</p><p class="story">...</p></body></html><head><title>The Dormouse‘s story</title></head><title>The Dormouse‘s story</title>The Dormouse‘s story<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 class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>,<a class="sister" href="http://example.com/lacie" id="link2">Lacie</a> and<a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>;and they lived at the bottom of a well.</p><p class="story">...</p></body><p class="title" name="dromouse"><b>The Dormouse‘s story</b></p><b>The Dormouse‘s story</b>The Dormouse‘s story<p class="story">Once upon a time there were three little sisters; and their names were<a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>,<a class="sister" href="http://example.com/lacie" id="link2">Lacie</a> and<a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>;and they lived at the bottom of a well.</p>Once upon a time there were three little sisters; and their names were<a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a> Elsie ,<a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>Lacie and<a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>Tillie;and they lived at the bottom of a well.<p class="story">...</p>..."""
如果tag只有一个 NavigableString 类型子节点,那么这个tag可以使用 .string 得到子节点。如果一个tag仅有一个子节点,那么这个tag也可以使用 .string 方法,输出结果与当前唯一子节点的 .string 结果相同。
print soup.head.string#The Dormouse‘s storyprint soup.title.string#The Dormouse‘s story
name参数可以查找所有名字为name的tag，字符串对象会被自动忽略掉。
在搜索方法中传入一个字符串参数，Beautiful Soup会查找与字符串完整匹配的内容
print(type(soup.find_all(‘p‘)))# <class ‘bs4.element.ResultSet‘ >print(soup.find_all(‘p‘))"""<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 class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>,<a class="sister" href="http://example.com/lacie" id="link2">Lacie</a> and<a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>;and they lived at the bottom of a well.</p>, <p class="story">...</p>]"""
如果传入正则表达式作为参数，Beautiful Soup会通过正则表达式的macth()来匹配内容。
# 找出所有以b开头的标签import refor tag in soup.find_all(re.compile(‘^b‘)): print(tag.name)# body# b
如果传入列表参数，Beautiful Soup会将把与列表中任一元素匹配的内容返回。
print(soup.find_all(["a",‘p‘]))"""[<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 class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>,<a class="sister" href="http://example.com/lacie" id="link2">Lacie</a> and<a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>;and they lived at the bottom of a well.</p>, <a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>, <a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>, <a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>, <p class="story">...</p>]"""
soup.find_all(id=‘link2‘)# [<a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>]
通过text参数可以搜索文档中的字符串内容，与name参数的可选值一样，text参数接受字符串、正则表达式及列表
import reprint(soup.find_all(text=‘Tillie‘))print(soup.find_all(text=["Tillie","Elsie","Lacie"]))print(soup.find_all(text=re.compile("Dormouse")))"""[‘Tillie‘][‘Lacie‘, ‘Tillie‘]["The Dormouse‘s story", "The Dormouse‘s story"]"""
写CSS时，标签名不加任何修饰，类名前加`.`，id名前加`#`
用soup.select()，返回类型是list
print(soup.select("title"))# [<title>The Dormouse‘s story</title>]print(soup.select("a"))"""[<a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>, <a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>, <a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>]"""print(soup.select(‘b‘))# [<b>The Dormouse‘s story</b>]
print(soup.select(".sister"))"""[<a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>, <a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>, <a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>]"""
print(soup.select("#link1"))# [<a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>]
组合查找即和写css文件时，标签名与类名、id名进行组合的原理是一样的，其各之间需要用空格分开。
print(soup.select("p #link1"))# [<a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>]
直接子标签查找，则使用`>`分隔
print(soup.select("head > title"))#[<title>The Dormouse‘s story</title>]
查找时还可以加入属性元素，属性需要用中括号括起来，注意属性与标签属于同一节点，所以中间不能加空格，否则会无法匹配到。
print(soup.select(‘a[class="sister"]‘))#[<a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>, <a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>, <a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>]print(soup.select(‘a[href="http://example.com/elsie"]‘))#[<a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>]
同样，属性仍然可以与上述查找方式组合，不在同一节点的空格隔开，同一节点的不加空格
print(soup.select(‘p a[href="http://example.com/elsie"]‘))#[<a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>]
select 方法返回的结果都是列表形式，可以遍历形式输出，然后用 get_text() 方法来获取它的内容。
soup = BeautifulSoup(html,‘lxml‘)print(type(soup.select("title")))# <class ‘bs4.element.ResultSet‘>print(soup.select(‘title‘)[0])# <title>The Dormouse‘s story</title>print(soup.select("title")[0].get_text())# The Dormouse‘s storyfor title in soup.select("title"): print(title.get_text())# The Dormouse‘s story
