BeautifulSoup爬取数据常用方法总结

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发布于 2022-11-27 10:55:57

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BeautifulSoup爬取数据常用方法总结

Beautiful Soup 是一个可以从HTML或XML文件中提取数据的Python库.它能够通过你喜欢的转换器实现惯用的文档导航,查找,修改文档的方式.Beautiful Soup会帮你节省数小时甚至数天的工作时间.

文章目录

安装BeautifulSoup

pip3 install -i https://pypi.tuna.tsinghua.edu.cn/simple beautifulsoup4

from bs4 import BeautifulSoup

素材

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

soup = BeautifulSoup(html_doc,"lxml")

几个简单的浏览结构化数据的方法

soup.title

<title>The Dormouse's story</title>

soup.title.name

'title'

soup.title.string

"The Dormouse's story"

soup.title.text

"The Dormouse's story"

soup.title.parent.name

'head'

soup.p

<p class="title"><b>The Dormouse's story</b></p>

soup.p.name

'p'

soup.p["class"]

['title']

soup.a

<a class="sister" href="http://example.com/elsie" id="link1">Elsie</a>

soup.find("a")

<a class="sister" href="http://example.com/elsie" id="link1">Elsie</a>

soup.find_all("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>]

从文档中找到所有的< a>标签的链接

for link in soup.find_all("a"):
    print(link.get("href"))

http://example.com/elsie
http://example.com/lacie
http://example.com/tillie

在文档中获取所有的文字内容

print(soup.get_text())

The Dormouse's story

The Dormouse's story
Once upon a time there were three little sisters; and their names were
Elsie,
Lacie and
Tillie;
and they lived at the bottom of a well.
...

常见解释器的优缺点

Tag

Tag有很多方法和属性,在遍历文档树和搜索文档树中有详细解释.现在介绍一下tag中最重要的属性: name和attributes

soup = BeautifulSoup('<b class="boldest">Extremely bold</b>')
tag  = soup.b
tag

<b class="boldest">Extremely bold</b>

type(tag)

bs4.element.Tag

Name

每个tag都有自己的名字,通过 .name 来获取:

tag.name

'b'

如果改变了tag的name,那将影响所有通过当前Beautiful Soup对象生成的HTML文档

tag.name = "blockquote"
tag

<blockquote class="boldest">Extremely bold</blockquote>

Attributes

一个tag可能有很多个属性.tag 有一个 “class” 的属性,值为 “boldest” . tag的属性的操作方法与字典相同:

tag["class"]

['boldest']

tag.attrs

{'class': ['boldest']}

tag的属性可以被添加,删除或修改. 再说一次, tag的属性操作方法与字典一样

tag["class"] = "verybold"
tag["id"] = 1
tag

<blockquote class="verybold" id="1">Extremely bold</blockquote>

del tag["class"]
tag

<blockquote id="1">Extremely bold</blockquote>

多值属性

css_soup = BeautifulSoup('<p class="body strikeout"></p>')
css_soup.p['class']

['body', 'strikeout']

css_soup = BeautifulSoup('<p class="body"></p>')
css_soup.p['class']

['body']

可以遍历的字符串

字符串常被包含在tag内.Beautiful Soup用 NavigableString 类来包装tag中的字符串:

tag.string

'Extremely bold'

type(tag.string)

bs4.element.NavigableString

一个 NavigableString 字符串与Python中的Unicode字符串相同, 并且还支持包含在遍历文档树和搜索文档树中的一些特性. 通过 unicode() 方法可以直接将 NavigableString 对象转换成Unicode字符串:
tag中包含的字符串不能编辑，但是可以被替换成其他的字符串，用replace_with()方法

tag.string.replace_with("No longer bold")
tag

<blockquote id="1">No longer bold</blockquote>

BeautifulSoup

BeautifulSoup 对象表示的是一个文档的全部内容.大部分时候,可以把它当作 Tag 对象,它支持遍历文档树和搜索文档树中描述的大部分的方法.

因为 BeautifulSoup 对象并不是真正的HTML或XML的tag,所以它没有name和attribute属性.但有时查看它的 .name 属性是很方便的,所以 BeautifulSoup 对象包含了一个值为 “[document]” 的特殊属性 .name

soup.name

'[document]'

注释及特殊字符串

文档的注释部分

markup = "<b><!--Hey, buddy. Want to buy a used parser?--></b>"
soup = BeautifulSoup(markup)
comment = soup.b.string
comment

'Hey, buddy. Want to buy a used parser?'

type(comment)

bs4.element.Comment

Comment 对象是一个特殊类型的 NavigableString 对象:

comment

'Hey, buddy. Want to buy a used parser?'

但是当它出现在HTML文档中时, Comment 对象会使用特殊的格式输出:

print(soup.prettify())

<html>
 <body>
  <b>
   <!--Hey, buddy. Want to buy a used parser?-->
  </b>
 </body>
</html>

from bs4 import CData
cdata = CData("A CDATA block")
comment.replace_with(cdata)
print(soup.b.prettify())

<b>
 <![CDATA[A CDATA block]]>
</b>

遍历文档树

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

from bs4 import BeautifulSoup

soup = BeautifulSoup(html_doc,"html.parser")

子节点

一个Tag可能包含多个字符串或其它的Tag,这些都是这个Tag的子节点.Beautiful Soup提供了许多操作和遍历子节点的属性.

soup.head

<head><title>The Dormouse's story</title></head>

soup.title

<title>The Dormouse's story</title>

这是个获取tag的小窍门,可以在文档树的tag中多次调用这个方法.下面的代码可以获取标签中的第一个标签:

soup.body.b

<b>The Dormouse's story</b>

通过点取属性的方式只能获得当前名字的第一个tag:

soup.a

<a class="sister" href="http://example.com/elsie" id="link1">Elsie</a>

- find_all

如果想要得到所有的标签,或是通过名字得到比一个tag更多的内容的时候,就需要用到 Searching the tree 中描述的方法,比如: find_all()

soup.find_all("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>]

.contents和.children

head_tag = soup.head
head_tag

<head><title>The Dormouse's story</title></head>

head_tag.contents

[<title>The Dormouse's story</title>]

head_tag.contents[0]

<title>The Dormouse's story</title>

head_tag.contents[0].contents

["The Dormouse's story"]

BeautifulSoup 对象本身一定会包含子节点,也就是说标签也是 BeautifulSoup 对象的子节点:

soup.contents

['\n',
 <html><head><title>The Dormouse's story</title></head>
 <body>
 <p class="title"><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>]