Python正则表达式基础

标签：find   图书   表示   nis   总结   换行   匹配   pytho   pat   

非Python独有,re模块实现

re.match

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

最常规的匹配

import re

content = ‘Hello 123 4567 World_This is a Regex Demo‘
result = re.match(‘^Hello\s\d\d\d\s\d{4}\s\w{10}.*Demo$‘,content)
print(result)
print(len(content))
 print(result.span())
print(result.group())

<_sre.SRE_Match object; span=(0, 41), match=‘Hello 123 4567 World_This is a Regex Demo‘>
41
(0, 41)
Hello 123 4567 World_This is a Regex Demo

泛匹配

import re
 
 content = ‘Hello 123 4567 World_This is a Regex Demo‘
 result = re.match(‘^Hello.*Demo$‘,content)
print(result)

<_sre.SRE_Match object; span=(0, 41), match=‘Hello 123 4567 World_This is a Regex Demo‘>

匹配目标

 content = ‘Hello 1234456 World, Nice_to meet u‘
 result = re.match(‘^Hello\s(\d+)\sWorld‘,content)
 print(result)
print(result.group(1))

<_sre.SRE_Match object; span=(0, 19), match=‘Hello 1234456 World‘>
1234456

贪婪匹配

content = ‘Hello 1234456 World, Nice to meet u_This is a Regex Demo‘

 result = re.match(‘^He.*(\d+).*Demo$‘,content)
 print(result)
 print(result.group(1))

<_sre.SRE_Match object; span=(0, 56), match=‘Hello 1234456 World, Nice to meet u_This is a Reg>
6 # .* 匹配到最后一个字符

非贪婪匹配

content = ‘Hello 1234456 World, Nice to meet u_This is a Regex Demo‘

result = re.match(‘^He.*?(\d+).*Demo$‘,content)
 print(result)
 print(result.group(1))

<_sre.SRE_Match object; span=(0, 56), match=‘Hello 1234456 World, Nice to meet u_This is a Reg>
1234456 # .*? 会匹配尽可能少的字符

匹配模式

. 本身不能匹配换行符

content = ‘‘‘Hello 1234456 World, Nice to meet u_This 
 is A Regex Demo
 ‘‘‘
 result = re.match(‘^He.*?(\d+).*Demo$‘,content)
 print(result)

None

加上第三个参数

 result = re.match(‘^He.*?(\d+).*Demo$‘,content,re.S)
 print(result)
 print(result.group(1))

<_sre.SRE_Match object; span=(0, 57), match=‘Hello 1234456 World, Nice to meet u_This \nis A R>
1234456

转义

content = ‘price is $5.00‘
result = re.match(‘price is $5.00‘,content)
print(result)

None
增加转义字符后：

result = re.match(‘price is \$5\.00‘,content)
print(result)

<_sre.SRE_Match object; span=(0, 14), match=‘price is $5.00‘>

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、有换行符就用re.S

re.search

re.search扫描整个字符串并返回第一个成功的匹配

import re
 
content = ‘Extra strings Hello 1234556 World_This is a Regex Demo Extra strings‘
result = re.match(‘Hello.*?(\d+).*?Demo‘,content)
print(result)

None

re.match没有找到字符

result = re.search(‘Hello.*?(\d+).*?Demo‘,content)
print(result)
print(result.group(1))

<_sre.SRE_Match object; span=(14, 54), match=‘Hello 1234556 World_This is a Regex Demo‘>
1234556
总结：为匹配方便，能用search就不用match

匹配演练

import re
 html = ‘‘‘<div id="songs-list">
   <h2 class="title">经典老歌</h2>
   <p class="introduction">经典老歌列表</p>
   <ul id="list" class="list-group">
     <li data-view="2">一路上有你</li>
     <li data-view="7">
       <a href="2.mp3" singer="任贤齐">沧海一声笑</a>
     </li>
     <li data-view="4" class="active">
       <a href="3.mp3" singer="齐秦">往事随风</a>
     </li>
     <li data-view="6"><a href="4.mp3" singer="beyond">光辉岁月</a></li>
    <li data-view="5"><a href="5.mp3" singer="陈慧琳">记事本</a></li>
     <li data-view="5">
       <a href="6.mp3" singer="邓丽君"><i class="fa fa-user"></i>但愿人长久</a>
     </li>
   </ul>
 </div>
 ‘‘‘

 result = re.search(‘<li.*?active.*?singer="(.*?)">(.*?)</a>‘,html,re.S)
 if result:
     print(result.group(1),result.group(2))
 

齐秦 往事随风

result = re.search(‘<li.*?singer="(.*?)">(.*?)</a>‘,html,re.S)
 if result:
     print(result.group(1),result.group(2))

任贤齐 沧海一声笑

默认匹配第一个

result = re.search(‘<li.*?singer="(.*?)">(.*?)</a>‘,html)
if result:
     print(result.group(1),result.group(2))

beyond 光辉岁月

去掉换行符后的输出结果

re.findall

搜索字符串，以列表形式返回全部匹配的子串

results = re.findall(‘<li.*?href="(.*?)".*?singer="(.*?)">(.*?)</a>‘,html,re.S)
print(results)

[(‘2.mp3‘, ‘任贤齐‘, ‘沧海一声笑‘), (‘3.mp3‘, ‘齐秦‘, ‘往事随风‘), (‘4.mp3‘, ‘beyond‘, ‘光辉岁月‘), (‘5.mp3‘, ‘陈慧琳‘, ‘记事本‘), (‘6.mp3‘, ‘邓丽君‘, ‘但愿人长久‘)]

for result in results:
     print(result[0],result[1],result[2])

2.mp3 任贤齐 沧海一声笑
3.mp3 齐秦 往事随风
4.mp3 beyond 光辉岁月
5.mp3 陈慧琳 记事本
6.mp3 邓丽君 但愿人长久

results = re.findall(‘<li.*?>\s*?(<a.*?>)?(\w+)(</a>)?\s*?</li>‘,html,re.S)
print(results)

[(‘‘, ‘一路上有你‘, ‘‘), (‘‘, ‘沧海一声笑‘, ‘‘), (‘‘, ‘往事随风‘, ‘‘), (‘‘, ‘光辉岁月‘, ‘‘), (‘‘, ‘记事本‘, ‘‘), (‘‘, ‘但愿人长久‘, ‘‘)]

 for result in results:
     print(result[1])

一路上有你
沧海一声笑
往事随风
光辉岁月
记事本
但愿人长久

re.sub

替换字符串中每一个匹配的子串后返回替换后的字符

content = ‘Extra strings Hello 1234567 World_This is a Regex Demo Extra strings‘
 content = re.sub(‘\d+‘,‘‘,content)
 print(content)

Extra strings Hello World_This is a Regex Demo Extra strings

content = ‘Extra strings Hello 1234567 World_This is a Regex Demo Extra strings‘
content = re.sub(‘\d+‘,‘Replacement‘,content)
print(content)

Extra strings Hello Replacement World_This is a Regex Demo Extra strings

字符"\1表示": 引用前面的字符串

content = ‘Extra strings Hello 1234567 World_This is a Regex Demo Extra strings‘
content = re.sub(‘(\d+)‘,r‘\1 8910‘,content)   
print(content)

Extra strings Hello 1234567 8910 World_This is a Regex Demo Extra strings

html = re.sub(‘<a.*?>|</a>‘,‘‘,html)
print(html)

 <div id="songs-list">
   <h2 class="title">经典老歌</h2>
   <p class="introduction">经典老歌列表</p>
   <ul id="list" class="list-group">
     <li data-view="2">一路上有你</li>
     <li data-view="7">
       沧海一声笑
     </li>
     <li data-view="4" class="active">
       往事随风
     </li>
     <li data-view="6">光辉岁月</li>
    <li data-view="5">记事本</li>
     <li data-view="5">
       <i class="fa fa-user"></i>但愿人长久
     </li>
   </ul>
 </div>

results = re.findall(‘<li.*?>(.*?)</li>‘,html,re.S)
print(results)

[‘一路上有你‘, ‘\n 沧海一声笑\n ‘, ‘\n 往事随风\n ‘, ‘光辉岁月‘, ‘记事本‘, ‘\n 但愿人长久\n ‘]

for result in results:
    print(result.strip())

一路上有你
沧海一声笑
往事随风
光辉岁月
记事本

re.compile

将正则字符串编译为正则表达式的对象，以便于复用该匹配模式

 content = ‘‘‘Hello 1234567 World_This
 is a Regex Demo‘‘‘
 pattern = re.compile(‘Hello.*Demo‘,re.S)
 result = re.match(pattern,content) 
 print(result)

<_sre.SRE_Match object; span=(0, 40), match=‘Hello 1234567 World_This\nis a Regex Demo‘>

实例练习

（会卡机的）
获取豆瓣图书信息

import requests
import re

content = requests.get(‘https://book.douban.com/‘).text
pattern = re.compile(‘<li.*?cover.*?href="(.*?)".*?alt="(.*?)".*?more-meta.*?author">(.*?)</span>.*?year">(.*?)</span>.*?</li>‘,re.S)
results = re.findall(pattern,content)
for result in results:
    url,name,author,date = result
    author = re.sub(‘\s‘,‘‘,author)
    date = re.sub(‘\s‘,‘‘,date)
    print(url,name,author,date)

Python正则表达式基础

标签：find   图书   表示   nis   总结   换行   匹配   pytho   pat   

原文地址：https://www.cnblogs.com/carious/p/10052038.html