Python 中正则表达式相关用法

正则模块re

安装

pip install re

使用

re.match()

按照规则进行匹配即可,规则如下:

• re.match('pattern',string,flags=0)

• re.match('pattern',string,flags=0) 其中pattern为要匹配的正则, string为要匹配的字符串,flags为标志位,返回一个匹配的对象.

• 可以使用group()拿到匹配之后的结果.

  In [1]: import re
  
  In [2]: re.match('www','www.baidu.com')
  Out[2]: <re.Match object; span=(0, 3), match='www'>
  
  In [3]: s = re.match('www','www.baidu.com')
  
  In [4]: print(s)
  <re.Match object; span=(0, 3), match='www'>
  
  In [5]: print(s.group())
  www
  

• re.match() 是按照从头开始进行匹配,如果首位匹配失败,则返回None

    In [3]: s = re.match('com','www.google.com')
    
    In [4]: print(s)
    None
  

re.search()

和 re.match()不同的是,re.search() 是扫描整个字符串并返回第一个匹配.

匹配规则如下:

• re.search('pattern',string,flags=0)

• pattern为要匹配的正则, string为要匹配的字符串,flags为标志位,返回一个匹配的对象.

• 可以使用group()拿到匹配之后的结果.

  In [5]: import re
  
  In [6]: l = re.search('com','www.google.com')
  
  In [7]: l
  Out[7]: <re.Match object; span=(11, 14), match='com'>
  
  In [8]: l.group()
  Out[8]: 'com'
  

re正则表达式规则

字符

.

• 可匹配除开换行符\n之外的所有字符

  In [13]: s = re.match('.','abc')
  
  In [14]: s
  Out[14]: <re.Match object; span=(0, 1), match='a'>
  
  
  In [16]: s = re.match('.','\sc')
  In [17]: s.group()
  Out[17]: '\\'
      
      
  In [27]: s = re.match('a.c','abc')
  In [28]: print(s)
  <re.Match object; span=(0, 3), match='abc'>
      
      
  

• 不能匹配换行符

  In [18]: s = re.match('.','\n')
  
  In [19]: s
  
  In [20]: s.group()
  ---------------------------------------------------------------------------
  AttributeError                            Traceback (most recent call last)
  <ipython-input-20-e3a70314fc21> in <module>
  ----> 1 s.group()
  
  AttributeError: 'NoneType' object has no attribute 'group'
  
  In [21]: print(s)
  None
  

• 在DOTALL模式中也能匹配换行符\n

  In [24]: s = re.match('.','\n',flags=re.DOTALL)
  
  In [25]: print(s)
  <re.Match object; span=(0, 1), match='\n'>
  
  In [26]: s.group()
  Out[26]: '\n'
  

\

• \是转义字符,能是一个字符改变为原来的意思

  In [2]: import re
  
  In [3]: s = re.match(r'a\\c','a\c')
  
  In [4]: s
  Out[4]: <re.Match object; span=(0, 3), match='a\\c'>
  
  In [5]: s.group()
  Out[5]: 'a\\c'
  
  In [6]: s = re.match(r'a\*c','a*c')
  
  In [7]: s
  Out[7]: <re.Match object; span=(0, 3), match='a*c'>
  
  In [8]: s.group()
  Out[8]: 'a*c'
  

[...]

• 字符集,对应的位置可以匹配字符集中的任意字符

  In [9]: s = re.match(r'a[bcd]e','abe')
  
  In [10]: s
  Out[10]: <re.Match object; span=(0, 3), match='abe'>
  
  In [11]: s.group()
  Out[11]: 'abe'
  
  In [12]: s = re.match(r'a[bcd]e','ade')
  
  In [13]: s.group()
  Out[13]: 'ade'
  

预定义字符集

\d

• 用于匹配[0-9]的数字

  In [15]: import re
  
  In [16]: re.match(r'a\dc','a1c')
  Out[16]: <re.Match object; span=(0, 3), match='a1c'>
  
  In [17]: s = re.match(r'a\dc','a1c')
  
  In [18]: s.group()
  Out[18]: 'a1c'
  

\D

• 用于匹配非数字

  In [19]: s = re.match(r'a\Dc','a1c')
  
  In [20]: s
  
  In [21]: print(s)
  None
  
  In [22]: s = re.match(r'a\Dc','afc')
  
  In [23]: print(s)
  <re.Match object; span=(0, 3), match='afc'>
  

\s

• 用于匹配空白字符

  In [24]: s = re.match(r'a\sc','a c')
  
  In [25]: print(s)
  <re.Match object; span=(0, 3), match='a c'>
  
  In [26]: s.group()
  Out[26]: 'a c'
  

\S

• 用于匹配非空白字符

  In [27]: s = re.match(r'a\Sc','asc')
  
  In [28]: s
  Out[28]: <re.Match object; span=(0, 3), match='asc'>
  
  In [29]: s.group()
  Out[29]: 'asc'
  

\w

• 匹配单词字符[A-Za-z0-9_],[]中均为单词字符

  
  In [30]: s = re.match(r'a\wc','asc')
  
  In [31]: s.group()
  Out[31]: 'asc'
  
  

\W

• 用于匹配非单词字符,如空格或者\n换行符

  In [32]: s = re.match(r'a\wc','a c')
  
  In [33]: s
  
  In [34]: print(s)
  None
  
  
  In [35]: s = re.match(r'a\wc','a\nc')
  
  In [36]: print(s)
  None
  

数量词

*

• 用于匹配前一个字符0或者无限次

  In [1]: import re
  
  In [2]: re.match('abc*','ab')
  Out[2]: <re.Match object; span=(0, 2), match='ab'>
  
  In [3]: s  = re.match('abc*','ab')
  
  In [4]: print(s)
  <re.Match object; span=(0, 2), match='ab'>
  
  In [5]: s.group()
  Out[5]: 'ab'
  
  In [6]: s  = re.match('abc*','abcccc')
  
  In [7]: print(s)
  <re.Match object; span=(0, 6), match='abcccc'>
  
  In [8]: s.group()
  Out[8]: 'abcccc'
  

+

• 用于匹配前一个字符1 次或者无限次

  In [9]: s  = re.match('abc+','ab')
  
  In [10]: s.group()
     ---------------------------------------------------------------------------
   AttributeError Traceback (most recent call last)
          <ipython-input-10-e3a70314fc21> in <module>
  
  In [12]: print(s)
  None
  
  
  In [13]: s  = re.match('abc+','abc')
  
  In [14]: s.group()
  Out[14]: 'abc'
    
  

?

• 用于匹配前一个字符0次或者一次

  In [27]:  s  = re.match('abc?','abc')
  
  In [28]: print(s)
  <re.Match object; span=(0, 3), match='abc'>
  
  In [29]:  s  = re.match('abc?','abcc')
  
  In [30]: print(s)
  <re.Match object; span=(0, 3), match='abc'>
  
  In [31]:  s  = re.match('abc?','ab')
  
  In [32]: print(s)
  <re.Match object; span=(0, 2), match='ab'>
  

{m}

• 用于匹配前一个字符m次

  In [34]:  s  = re.match('ab{2}c','abbc')
  
  In [35]: s.group()
  Out[35]: 'abbc'
  
  
  In [36]:  s  = re.match('ab{2}c','abc')
  In [38]: print(s)
  None
  

组合使用

一般情形下, Python中的re正则表达式都是组合进行使用字符,预定义字符集和数量词.构建正则匹配的规则.

示例: 匹配邮箱正则表达式

In [39]: email = "king-nova@gmail.com"

In [40]: s = re.match(r'^[\.A-Za-z0-9_-]+@[A-Za-z0-9_-]+(\.[A-Za-z0-9_-]+)+$', email)

In [41]: s
Out[41]: <re.Match object; span=(0, 19), match='king-nova@gmail.com'>

In [42]: s.group()
Out[42]: 'king-nova@gmail.com'