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BeautifulSoup的用法详解

妖妖妈 2022-05-13 阅读 75
pythonhtmlicoJava编程语言

糯米


2020.08.25

网络爬虫

Web spider

and information extraction

BeautifulSoup的用法详解_html

BeautifulSoup库是

解析、遍历、维护“标签书”的功能库

将html，xml等文档解析加工，供人类利用

下面介绍它的用法。​

​

1

BeautifulSoup库介绍

html文件理解示例图：

BeautifulSoup的用法详解_python_02


​

​

​我们使用​​from bs4 import BeautifulSoup4​​来导入BeautifulSoup，下面给出解析html的示例语句：

>>> from bs4 import BeautifulSoup
>>> soup = BeautifulSoup("<html>data</html>", "html.parser")
>>> soup2 = BeautifulSoup(open("D://demo.html"), "html.parser")


除了HTML解析器，我们还可以使用其他解析器，如下：

​

BeautifulSoup的用法详解_ico_03



01

BeautifulSoup


类的基本元素


01

Tag

标签，最基本的信息组织单元，分别用<>和</>标明开头和结尾

02

Name

标签的名字，< p >…< /p >的名子是’p’，格式：.name

03

Attributes

标签的属性，字典形式组织，格式：< tag >.attrs

04

NavigableString

标签内非属性字符串，<>…</>中字符串，格式：< tag >.string

05

Comment

标签内字符串的注释部分，一种特殊的Comment类型


BeautifulSoup的用法详解_html_04

>>

<<

BeautifulSoup的用法详解_html_05

2

BeautifulSoup的使用

​先给出一个网址，接下来的教程都会围绕这个url展开​

https://python123.io/ws/demo.html


以下的操作都在Python的IDLE里进行，大家可以跟着敲一遍，方便理解记忆。

首先我们需要先定义一个demo，以下操作都会利用demo，不再重复解释和定义。

>>> import requests
>>> r = requests.get(demo)
>>> demo = r.text


首先我们来解析这个demo看看：

soup = BeautifulSoup(demo, "html.parser")
print(soup.prettify())


然后我们会看到返回的结果

<html>
 <head>
  <title>
   This is a python demo page
  </title>
 </head>
 <body>
  <p class="title">
   <b>
    The demo python introduces several python courses.
   </b>
  </p>
  <p class="course">
   Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:
   <a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">
    Basic Python
   </a>
   and
   <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">
    Advanced Python
   </a>
   .
  </p>
 </body>
</html>


这样的代码更适合我们的解读

总结下来使用BeautifulSoup库只需两行代码：

from bs4 import BeautifulSoup
soup = BeautifulSoup('<p>data</p>', 'html.parser')


其中< p >data< /p >为html的信息

我们可以获取单独标签的内容：

>>> soup.title
<title>This is a python demo page</title>
>>> tag = soup.a
>>> tag
<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>


这种方式若有多个相同名字的标签，默认只获得第一个

同样我们也可以获得标签的名字：

>>> soup.a.name
'a'
>>> soup.title.name
'title'


下面我们获得标签的属性：

>>> tag = soup.a
>>> tag.attrs
{'href': 'http://www.icourse163.org/course/BIT-268001', 'class': ['py1'], 'id': 'link1'}


我们可以看到他是一个字典

所以我们也可以单独查看某一属性的属性：

>>> tag.attrs['class']
['py1']
>>> tag.attrs['href']
'http://www.icourse163.org/course/BIT-268001'


我们也可以查看标签的类型：

>>> type(tag.attrs)
<class 'dict'>
>>> type(tag)
<class 'bs4.element.Tag'>


当标签无属性时返回空字典

我们还可以查看标签尖括号之间的的字符串：

>>> soup.a
<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>
>>> soup.a.string
'Basic Python'
>>> soup.p
<p class="title"><b>The demo python introduces several python courses.</b></p>
>>> soup.p.string
'The demo python introduces several python courses.'
>>> type(soup.p.string)
<class 'bs4.element.NavigableString'>



BeautifulSoup的用法详解_html_06

BeautifulSoup的用法详解_html_06

BeautifulSoup的用法详解_html_06


3

BeautifulSoup标签的遍历


01

BeautifulSoup


的下行遍历

​

01

.contents

子节点的列表，将**< tag >**所有的儿子节点存入列表​

02

.children

子节点的迭代类型，与**.contents**类似，用于循环儿子节点

03

.descendent

子孙节点的迭代类型，包含所有的子孙节点，用于循环遍历


下面举个例子：

>>> soup.head
<head><title>This is a python demo page</title></head>
>>> soup.head.contents
[<title>This is a python demo page</title>]
>>> soup.body.contents
['\n', <p class="title"><b>The demo python introduces several python courses.</b></p>, '\n', <p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:


<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a> and <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>.</p>, '\n']
>>> len(soup.body.contents)
5
>>> soup.body.contents[1]
<p class="title"><b>The demo python introduces several python courses.</b></p>





02

BeautifulSoup


的上行遍历


01

.parent

节点的父亲节点

02

.parents

结点的先辈标签的迭代类型，用于循环遍历先辈节点


下面举个例子：

>>> soup.title.parent
<head><title>This is a python demo page</title></head>
>>> soup.html.parent
<html><head><title>This is a python demo page</title></head>
<body>
<p class="title"><b>The demo python introduces several python courses.</b></p>
<p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:


<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a> and <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>.</p>
</body></html>
>>> soup.parent
>>>

如上我们可以看出，由于html标签无父节点，所以返回它自身，而soup无parent所以返回空。



03

BeautifulSoup


的平行遍历


Rsponse对象：

01

.next_sibling

返回按照HTML文本顺序的下一个平行节点标签

02

​.prevous_sibling

返回按照HTML文本顺序的上一个平行节点标签

03

.next_siblings

迭代类型，返回按照HTML文本顺序的后续所有平行节点标签

04

.previous_siblings

迭代类型，返回按照HTML文本顺序的前续所有平行节点标签


​


下面举个例子：

>>> soup.a.next_sibling
' and '
>>> soup.a.next_sibling.next_sibling
<a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>
>>> soup.a.previous_sibling
'Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:\r\n'
>>> soup.a.previous_sibling.previous_sibling
>>>

平行遍历返回的也可能是String类型，不全是标签类型。同时我们可以看到a节点没有前一个结点的前一个结点，所以返回空。



03

BeautifulSoup


信息的提取

​<>.find_all(anme, attrs, recursive, string, **kwargs)

返回一个列表，可以在soup中查找想要的信息


01


​

name

​对标签名称的检索字符串

02

attrs

对标签属性值的检索字符串，可标注属性检索

03

recursive

是否对子孙全部检索，默认为True

04

string

<>…</>中字符串区域的检索字符串


下面举个例子：

>>> soup.find_all('a')
[<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>, <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>]
>>> soup.find_all(['a','b'])
[<b>The demo python introduces several python courses.</b>, <a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>, <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>]
>>> soup.find_all(True)
[<html><head><title>This is a python demo page</title></head>
<body>
<p class="title"><b>The demo python introduces several python courses.</b></p>
<p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:


<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a> and <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>.</p>
</body></html>, <head><title>This is a python demo page</title></head>, <title>This is a python demo page</title>, <body>
<p class="title"><b>The demo python introduces several python courses.</b></p>
<p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:


<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a> and <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>.</p>
</body>, <p class="title"><b>The demo python introduces several python courses.</b></p>, <b>The demo python introduces several python courses.</b>, <p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:


<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a> and <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>.</p>, <a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>, <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>]

若参数为True则返回所有信息。
我们也可以对属性进行约束：

>>> soup.find_all(id='link1')
[<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>]
>>> soup.find_all(id='link')
[]

​

若标签不存在则返回空列表。


我们默认搜索从当前节点的所有节点，我们可以将recursive置为False，只查找儿子节点：

>>> soup.find_all('a')
[<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>, <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>]
>>> soup.find_all('a', recursive=False)
[]

​

返回空节点，由此看出soup的儿子节点无a标签。


我们也可以检索字符串：

>>> soup.find_all(string = 'Basic Python')
['Basic Python']

以上可以用<tag>(…)代替<tag>.find_all(…)

使用soup(…)代替soup.find_all(…)

同时我们还有其他的扩展方法：

BeautifulSoup的用法详解_ico_09



下面给大家一个爬虫实例：

#中国大学排名定向爬虫
import requests
from bs4 import BeautifulSoup
import bs4
def getHTMLText(url):
    try:
        r = requests.get(url, timeout=30)
        r.raise_for_status()
        r.encoding = r.apparent_encoding
        return r.text
    except:
        return ""
def fillUnivList(ulist, html):
    soup = BeautifulSoup(html, "html.parser")
    for tr in soup.find('tbody').children:
        if isinstance(tr, bs4.element.Tag):
            tds = tr('td')
            ulist.append([tds[0].string, tds[1].string, tds[3].string])
def printUnivList(ulist, num):
    tplt = "{0:^10}\t{1:{3}^10}\t{2:^10}"
    print(tplt.format("排名","学校名称","总分",chr(12288)))
    for i in range(num):
        u=ulist[i]
        print(tplt.format(u[0],u[1],u[2],chr(12288)))
def main():
    uinfo = []
    url = 'http://www.zuihaodaxue.com/zuihaodaxuepaiming2019.html'
    html = getHTMLText(url)
    fillUnivList(uinfo, html)
    printUnivList(uinfo, 20) # 20 univs
main()


END

​

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