欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识!
您现在的位置是: 首页  >  IT编程

Python爬虫之正则表达式的使用教程详解

程序员文章站 2022-07-10 12:06:58
正则表达式的使用 re.match(pattern,string,flags=0) re.match尝试从字符串的起始位置匹配一个模式,如果不是起始位置匹配成功的话,m...

正则表达式的使用

re.match(pattern,string,flags=0)

re.match尝试从字符串的起始位置匹配一个模式,如果不是起始位置匹配成功的话,match()就返回none

参数介绍:

pattern:正则表达式

string:匹配的目标字符串

flags:匹配模式

正则表达式的匹配模式:

Python爬虫之正则表达式的使用教程详解

最常规的匹配

import re
content ='hello 123456 world_this is a regex demo'
print(len(content))
result = re.match('^hello\s\d{6}\s\w{10}.*demo$$',content)
print(result)
print(result.group()) #返回匹配结果
print(result.span()) #返回匹配结果的范围

结果运行如下:

39
<_sre.sre_match object; span=(0, 39), match='hello 123456 world_this is a regex demo'>
hello 123456 world_this is a regex demo
(0, 39)

泛匹配

使用(.*)匹配更多内容

import re
content ='hello 123456 world_this is a regex demo'
result = re.match('^hello.*demo$',content)
print(result)
print(result.group())

结果运行如下:

<_sre.sre_match object; span=(0, 39), match='hello 123456 world_this is a regex demo'>
hello 123456 world_this is a regex demo

匹配目标

在正则表达式中使用()将要获取的内容括起来

使用group(1)获取第一处,group(2)获取第二处,如此可以提取我们想要获取的内容

import re
content ='hello 123456 world_this is a regex demo'
result = re.match('^hello\s(\d{6})\s.*demo$',content)
print(result)
print(result.group(1))#获取匹配目标

结果运行如下:

<_sre.sre_match object; span=(0, 39), match='hello 123456 world_this is a regex demo'>
123456

贪婪匹配

import re
content ='hello 123456 world_this is a regex demo'
result = re.match('^he.*(\d+).*demo$',content)
print(result)
print(result.group(1))

注意:.*会尽可能的多匹配字符

非贪婪匹配

import re
content ='hello 123456 world_this is a regex demo'
result = re.match('^he.*?(\d+).*demo$',content)
print(result)
print(result.group(1)) 

注意:.*?会尽可能匹配少的字符

使用匹配模式

在解析html代码时会有换行,这时我们就要使用re.s

import re
content ='hello 123456 world_this ' \
'is a regex demo'
result = re.match('^he.*?(\d+).*?demo$',content,re.s)
print(result)
print(result.group(1))

运行结果如下:

<_sre.sre_match object; span=(0, 39), match='hello 123456 world_this is a regex demo'>
123456

转义

在解析过程中遇到特殊字符,就需要做转义,比如下面的$符号。

import re
content = 'price is $5.00'
result = re.match('^price.*\$5\.00',content)
print(result.group())

总结:尽量使用泛匹配,使用括号得到匹配目标,尽量使用非贪婪模式,有换行就用re.s

re.search(pattern,string,flags=0)

re.search扫描整个字符串并返回第一个成功的匹配。

比如我想要提取字符串中的123456,使用match方法无法提取,只能使用search方法。

import re
content ='hello 123456 world_this is a regex demo'
result = re.match('\d{6}',content)
print(result)
import re
content ='hello 123456 world_this is a regex demo'
result = re.search('\d{6}',content)
print(result)
print(result.group())

运行结果如下:

<_sre.sre_match object; span=(6, 12), match='123456'>

匹配演练

可以匹配代码里结构相同的部分,这样可以返回你需要的内容

import re
content = '<a title="2009年中信出版社出版图书" href="/doc/2703035-2853985.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" target="_blank" data-log="old:2703035-2853885,new:2703035-2853985" data-cid="sense-list">2009年中信出版社出版图书</a>'
result = re.search('<a.*?new:\d{7}-\d{7}.*?>(.*?)</a>',content)
print(result.group(1))
2009年中信出版社出版图书
re.findall(pattern,string,flags=0)

搜索字符串,以列表形式返回全部能匹配的字串

import re
html ='''
<li>
<a title="网络歌曲" href="/doc/2703035-2853927.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" target="_blank" data-log="old:2703035-2853885,new:2703035-2853927" data-cid="sense-list">网络歌曲</a>
</li>
<li>
<a title="2009年中信出版社出版图书" href="/doc/2703035-2853985.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" target="_blank" data-log="old:2703035-2853885,new:2703035-2853985" data-cid="sense-list">2009年中信出版社出版图书</a>
</li>
'''
result = re.findall('<a.*?new:\d{7}-\d{7}.*?>(.*?)</a>',html,re.s)
count = 0
for list in result:
  print(result[count])
  count+=1
网络歌曲
2009年中信出版社出版图书
re.sub( pattern,repl,string,count,flags)

re.sub共有五个参数

三个必选参数 pattern,repl,string

两个可选参数count,flags

替换字符串中每一个匹配的字符串后替换后的字符串

import re
content = 'hello 123456 world_this is a regex demo'
content = re.sub('\d+','',content)
print(content)

运行结果如下:

hello  world_this is a regex demo
import re
content = 'hello 123456 world_this is a regex demo'
content = re.sub('\d+','what',content)
print(content)

运行结果如下:

hello what world_this is a regex demo
import re
content = 'hello 123456 world_this is a regex demo'
content = re.sub('(\d+)',r'\1 789',content)
print(content)

运行结果如下:

hello 123456 789 world_this is a regex demo

注意:这里\1代表前面匹配的123456

演练

在这里我们替换li标签

import re
html ='''
<li>
<a title="网络歌曲" href="/doc/2703035-2853927.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" target="_blank" data-log="old:2703035-2853885,new:2703035-2853927" data-cid="sense-list">网络歌曲</a>
</li>
<li>
<a title="2009年中信出版社出版图书" href="/doc/2703035-2853985.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" target="_blank" data-log="old:2703035-2853885,new:2703035-2853985" data-cid="sense-list">2009年中信出版社出版图书</a>
</li>
'''
html = re.sub('<li>|</li>','',html)
print(html)

运行结果如下,里面就没有li标签

<a title="网络歌曲" href="/doc/2703035-2853927.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" target="_blank" data-log="old:2703035-2853885,new:2703035-2853927" data-cid="sense-list">网络歌曲</a>
<a title="2009年中信出版社出版图书" href="/doc/2703035-2853985.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" target="_blank" data-log="old:2703035-2853885,new:2703035-2853985" data-cid="sense-list">2009年中信出版社出版图书</a>
compile(pattern [, flags])

该函数根据包含的正则表达式的字符串创建模式对象。可以实现更有效率的匹配

将正则表达式编译成正则表达式对象,以便于复用该匹配模式

import re
content = 'hello 123456 ' \
'world_this is a regex demo'
pattern = re.compile('hello.*?demo',re.s)
result = re.match(pattern,content)
print(result.group()) 

运行结果如下:

hello 123456 world_this is a regex demo

综合使用

import re
html = '''
<div class="slide-page" style="width: 700px;" data-index="1">
    <a class="item" target="_blank" href="https://movie.douban.com/subject/26725678/?tag=热门&from=gaia">
      <div class="cover-wp" data-isnew="false" data-id="26725678">
        <img src="https://img1.doubanio.com/view/photo/s_ratio_poster/public/p2525020357.jpg" alt="解除好友2:暗网" data-x="694" data-y="1000">
      </div>
      <p>
        解除好友2:暗网
          <strong>7.9</strong>
      </p>
    </a>
    <a class="item" target="_blank" href="https://movie.douban.com/subject/26916229/?tag=热门&from=gaia_video">
      <div class="cover-wp" data-isnew="false" data-id="26916229">
        <img src="https://img1.doubanio.com/view/photo/s_ratio_poster/public/p2532008868.jpg" alt="镰仓物语" data-x="2143" data-y="2993">
      </div>
      <p>
        镰仓物语
          <strong>6.9</strong>
      </p>
    </a>
    <a class="item" target="_blank" href="https://movie.douban.com/subject/26683421/?tag=热门&from=gaia">
      <div class="cover-wp" data-isnew="false" data-id="26683421">
        <img src="https://img3.doubanio.com/view/photo/s_ratio_poster/public/p2528281606.jpg" alt="特工" data-x="690" data-y="986">
      </div>
      <p>
        特工
          <strong>8.3</strong>
      </p>
    </a>
    <a class="item" target="_blank" href="https://movie.douban.com/subject/27072795/?tag=热门&from=gaia">
      <div class="cover-wp" data-isnew="false" data-id="27072795">
        <img src="https://img3.doubanio.com/view/photo/s_ratio_poster/public/p2521583093.jpg" alt="幸福的拉扎罗" data-x="640" data-y="914">
      </div>
      <p>
        幸福的拉扎罗
          <strong>8.6</strong>
      </p>
    </a>
    <a class="item" target="_blank" href="https://movie.douban.com/subject/27201353/?tag=热门&from=gaia_video">
      <div class="cover-wp" data-isnew="false" data-id="27201353">
        <img src="https://img1.doubanio.com/view/photo/s_ratio_poster/public/p2528842218.jpg" alt="大师兄" data-x="679" data-y="950">
      </div>
      <p>
        大师兄
          <strong>5.2</strong>
      </p>
    </a>
    <a class="item" target="_blank" href="https://movie.douban.com/subject/30146756/?tag=热门&from=gaia_video">
      <div class="cover-wp" data-isnew="false" data-id="30146756">
        <img src="https://img3.doubanio.com/view/photo/s_ratio_poster/public/p2530872223.jpg" alt="风语咒" data-x="1079" data-y="1685">
      </div>
      <p>
        风语咒
          <strong>6.9</strong>
      </p>
    </a>
    <a class="item" target="_blank" href="https://movie.douban.com/subject/26630714/?tag=热门&from=gaia">
      <div class="cover-wp" data-isnew="false" data-id="26630714">
        <img src="https://img3.doubanio.com/view/photo/s_ratio_poster/public/p2530591543.jpg" alt="精灵旅社3:疯狂假期" data-x="1063" data-y="1488">
      </div>
      <p>
        精灵旅社3:疯狂假期
          <strong>6.8</strong>
      </p>
    </a>
    <a class="item" target="_blank" href="https://movie.douban.com/subject/25882296/?tag=热门&from=gaia_video">
      <div class="cover-wp" data-isnew="false" data-id="25882296">
        <img src="https://img3.doubanio.com/view/photo/s_ratio_poster/public/p2526405034.jpg" alt="狄仁杰之四大天王" data-x="2500" data-y="3500">
      </div>
      <p>
        狄仁杰之四大天王
          <strong>6.2</strong>
      </p>
    </a>
    <a class="item" target="_blank" href="https://movie.douban.com/subject/26804147/?tag=热门&from=gaia_video">
      <div class="cover-wp" data-isnew="false" data-id="26804147">
        <img src="https://img3.doubanio.com/view/photo/s_ratio_poster/public/p2527484082.jpg" alt="摩天营救" data-x="1371" data-y="1920">
      </div>
      <p>
        摩天营救
          <strong>6.4</strong>
      </p>
    </a>
    <a class="item" target="_blank" href="https://movie.douban.com/subject/24773958/?tag=热门&from=gaia_video">
      <div class="cover-wp" data-isnew="false" data-id="24773958">
        <img src="https://img3.doubanio.com/view/photo/s_ratio_poster/public/p2517753454.jpg" alt="复仇者联盟3:无限战争" data-x="1968" data-y="2756">
      </div>
      <p>
        复仇者联盟3:无限战争
          <strong>8.1</strong>
      </p>
    </a>
  </div>
'''
count = 0
for list in result:
  print(result[count])
  count+=1

运行结果如下:

('解除好友2:暗网', '7.9')
('镰仓物语', '6.9')
('特工', '8.3')
('幸福的拉扎罗', '8.6')
('大师兄', '5.2')
('风语咒', '6.9')
('精灵旅社3:疯狂假期', '6.8')
('狄仁杰之四大天王', '6.2')
('摩天营救', '6.4')
('复仇者联盟3:无限战争', '8.1')

总结

以上所述是小编给大家介绍的python爬虫之正则表达式的使用教程,希望对大家有所帮助