第34篇：Python正则表达式

一、re模块常用方法：

1. match()

match(pattern, string, flags=0)

match()函数只检测字符串开头位置是否匹配，匹配成功才会返回结果，否则返回None

• 正则表达式
• 要匹配的字符串
• 标志位，用于控制正则表达式的匹配方式

import re
 
obj = re.match('\d+', '123uuasf')
if obj:
    print(obj.group())

2. search()

search(pattern, string, flags=0)

search()函数会在整个字符串内查找模式匹配,只到找到第一个匹配然后返回一个包含匹配信息的对象,该对象可以通过调用group()方法得到匹配的字符串,如果字符串没有匹配，则返回None。

import re
 
obj = re.search('\d+', 'u123uu888asf')
if obj:
    print(obj.group())

3. group和groups

a = "123abc456"
print re.search("([0-9]*)([a-z]*)([0-9]*)", a).group()
 
print re.search("([0-9]*)([a-z]*)([0-9]*)", a).group(0)
print re.search("([0-9]*)([a-z]*)([0-9]*)", a).group(1)
print re.search("([0-9]*)([a-z]*)([0-9]*)", a).group(2)
 
print re.search("([0-9]*)([a-z]*)([0-9]*)", a).groups()

4. findall()

findall(pattern, string, flags=0)

上述两中方式均用于匹配单值，即：只能匹配字符串中的一个，如果想要匹配到字符串中所有符合条件的元素，则需要使用 findall。

import re
 
obj = re.findall('\d+', 'fa123uu888asf')
print(obj)
# ['123', '888']

5. sub()

sub(pattern, repl, string, count=0, flags=0)

用于替换匹配的字符串

content = "123abc456"
new_content = re.sub('\d+', 'sb', content)
# new_content = re.sub('\d+', 'sb', content, 1)
print(new_content)
sbabcsb

相比于str.replace功能更加强大

6. split()

split(pattern, string, maxsplit=0, flags=0)

根据指定匹配进行分组

content = "'1 - 2 * ((60-30+1*(9-2*5/3+7/3*99/4*2998+10*568/14))-(-4*3)/(16-3*2) )'"
new_content = re.split('\*', content)
# new_content = re.split('\*', content, 1)
print(new_content)
["'1 - 2 ", ' ((60-30+1', '(9-2', '5/3+7/3', '99/4', '2998+10', '568/14))-(-4', '3)/(16-3', "2) )'"]
 
content = "'1 - 2 * ((60-30+1*(9-2*5/3+7/3*99/4*2998+10*568/14))-(-4*3)/(16-3*2) )'"
new_content = re.split('[\+\-\*\/]+', content)
# new_content = re.split('\*', content, 1)
print(new_content)
["'1 ", ' 2 ', ' ((60', '30', '1', '(9', '2', '5', '3', '7', '3', '99', '4', '2998', '10', '568', '14))', '(', '4', '3)', '(16', '3', "2) )'"]
 
inpp = '1-2*((60-30 +(-40-5)*(9-2*5/3 + 7 /3*99/4*2998 +10 * 568/14 )) - (-4*3)/ (16-3*2))'
inpp = re.sub('\s*','',inpp)
new_content = re.split('\(([\+\-\*\/]?\d+[\+\-\*\/]?\d+){1}\)', inpp, 1)
print(new_content)
['1-2*((60-30+', '-40-5', '*(9-2*5/3+7/3*99/4*2998+10*568/14))-(-4*3)/(16-3*2))']

相比于str.split更加强大

二、单字符匹配

字符	功能
.	匹配任意1个字符（除了\n），注意因为.表示任意一个字符，所以如果匹配‘.’则需要用转义字符.来表示
[ ]	匹配[ ]中列举的字符，如果[a-zA-Z0-9],[a-zA-Z]表示所有字母和数字，后者表示所有字母，注意中间没有空格符号。
\d	匹配数字，即0-9
\D	匹配非数字，即不是数字
\s	匹配空白，即 空格，tab键
\S	匹配非空白
\w	匹配单词字符，即a-z、A-Z、0-9、_
\W	匹配非单词字符

单字符匹配案例

In [8]: ma = re.match(r'.','b')

In [9]: ma.gro
ma.group      ma.groupdict  ma.groups     

In [9]: ma.group()
Out[9]: 'b'

In [10]: ma = re.match(r'.','0')

In [11]: ma.grou
ma.group      ma.groupdict  ma.groups     

In [11]: ma.group()
Out[11]: '0'

In [12]: clear


In [13]: ma = re.match(r'{.}','{a}')

In [14]: ma.group()
Out[14]: '{a}'

In [15]: ma = re.match(r'{.}','{0}')

In [16]: ma.grou
ma.group      ma.groupdict  ma.groups     

In [16]: ma.group()
Out[16]: '{0}'

In [17]: ma = re.match(r'{..}','{01}')

In [18]: ma.group()
Out[18]: '{01}'

In [19]: ma = re.match(r'{[abc]}','{a}')

In [20]: ma.group()
Out[20]: '{a}'

In [21]: ma = re.match(r'{[a-z]}','{d}')

In [22]: ma.group()
Out[22]: '{d}'

In [23]: ma = re.match(r'{[a-zA-Z]}','{A}')

In [24]: ma.group()
Out[24]: '{A}'

In [25]: ma = re.match(r'{[a-zA-Z0-9]}','{0}')

In [26]: ma.group()
Out[26]: '{0}'

In [27]: ma = re.match(r'{[\w]}','{ }')

In [28]: ma

In [29]: ma = re.match(r'{[\W]}','{ }')

In [30]: ma
Out[30]: <_sre.SRE_Match object; span=(0, 3), match='{ }'>

In [31]: ma.group()
Out[31]: '{ }'

In [32]: ma = re.match(r'{[\W]}','{9}')

In [33]: ma.group()
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-33-7c62fc675aee> in <module>()
----> 1 ma.group()

AttributeError: 'NoneType' object has no attribute 'group'

In [34]: ma

In [35]: ma = re.match(r'[[\w]]','[a]')

In [36]: ma

In [37]: ma = re.match(r'\[[\w]\]','[a]')

In [38]: ma.group()
Out[38]: '[a]'

In [39]: ma = re.match(r'\[[\w]\]','[0]')

In [40]: ma.group()
Out[40]: '[0]'

三、表示数量

字符	功能
*	匹配前一个字符出现0次或者无限次，即可有可无
+	匹配前一个字符出现1次或者无限次，即至少有1次
?	匹配前一个字符出现1次或者0次，即要么有1次，要么没有
{m}	匹配前一个字符出现m次
{m,}	匹配前一个字符至少出现m次
{m,n}	匹配前一个字符出现从m到n次

多个字符匹配案例

In [1]: import re

In [2]: ma = re.match(r'[A-Z][a-z]','Aa')

In [3]: ma.grou
ma.group      ma.groupdict  ma.groups     

In [3]: ma.group()
Out[3]: 'Aa'

In [4]: ma = re.match(r'[A-Z][a-z]','A')

In [6]: ma

In [8]: 

In [8]: ma = re.match(r'[A-Z][a-z]*','A')

In [9]: ma
Out[9]: <_sre.SRE_Match object; span=(0, 1), match='A'>

In [10]: ma.group()
Out[10]: 'A'
In [12]: ma = re.match(r'[A-Z][a-z]*','Asdsdwqass')

In [14]: ma.
ma.end        ma.group      ma.lastgroup  ma.re         ma.start
ma.endpos     ma.groupdict  ma.lastindex  ma.regs       ma.string
ma.expand     ma.groups     ma.pos        ma.span       

In [14]: ma.group()
Out[14]: 'Asdsdwqass'

In [15]: ma = re.match(r'[A-Z][a-z]*','1Asdsdwqass')

In [16]: ma

In [17]: ma = re.match(r'[A-Z][a-z]*','Asd1sdwqass')

In [18]: ma.group()
Out[18]: 'Asd'

In [19]: ma = re.match(r'[_a-zA-Z]+[_\w]*','10')

In [20]: ma

In [21]: ma = re.match(r'[_a-zA-Z]+[_\w]*','_ht11')

In [22]: ma.group()
Out[22]: '_ht11'

In [23]: ma = re.match(r'[1-9]?[0-9]','99')

In [24]: ma.group()
Out[24]: '99'

In [25]: ma = re.match(r'[1-9]?[0-9]','90')

In [26]: ma.group()
Out[26]: '90'

In [27]: ma = re.match(r'[1-9]?[0-9]','9')

In [28]: ma.group()
Out[28]: '9'

In [29]: ma = re.match(r'[1-9]?[0-9]','0')

In [30]: ma.group()
Out[30]: '0'

In [31]: ma = re.match(r'[1-9]?[0-9]','09')

In [32]: ma.group()
Out[32]: '0'

In [33]: ma = re.match(r'[[a-zA-Z0-9]{6}','abc123')

In [34]: ma.group()
Out[34]: 'abc123'

In [35]: ma = re.match(r'[[a-zA-Z0-9]{6}','abc1234')

In [36]: ma.group()
Out[36]: 'abc123'

In [37]: ma = re.match(r'[[a-zA-Z0-9]{6}','abc1__')

In [38]: ma

In [39]: ma = re.match(r'[[a-zA-Z0-9]{6}@163.com','abc123@163.com')

In [40]: ma.group()
Out[40]: 'abc123@163.com'

In [41]: ma = re.match(r'[[a-zA-Z0-9]{6,10}@163.com','abc1234@163.com')

In [42]: ma.grou
ma.group      ma.groupdict  ma.groups     

In [42]: ma.group()
Out[42]: 'abc1234@163.com'

In [43]: ma = re.match(r'[0-9][a-z]*?','1bc')

In [44]: ma.group()
Out[44]: '1'

In [45]: ma = re.match(r'[0-9][a-z]*','1bc')

In [46]: ma.group()
Out[46]: '1bc'

四、表示边界

字符	功能
^	匹配字符串开头
$	匹配字符串结尾
\b	匹配一个单词边界，也就是指单词和空格间的位置。例如， ‘er\b’ 可以匹配”never” 中的 ‘er’，但不能匹配 “verb” 中的 ‘er’。
\B	匹配非单词边界，’er\B’ 能匹配 “verb” 中的 ‘er’，但不能匹配 “never” 中的 ‘er’。

表示边界

In [48]: ma = re.match(r'[[a-zA-Z0-9]{6,10}@163.com','abc1234@163.comabc') 

In [49]: ma.group()
Out[49]: 'abc1234@163.com'

In [50]: ma = re.match(r'[[a-zA-Z0-9]{6,10}@163.com$','abc1234@163.comabc')

In [51]: ma

In [52]: ma = re.match(r'^[[a-zA-Z0-9]{6,10}@163.com$','abc1234@163.com')
In [53]: ma.group()
Out[53]: 'abc1234@163.com'

In [54]: ma = re.match(r'\Aimooc[\w]*','imoocpython')

In [55]: ma.group()
Out[55]: 'imoocpython'

In [56]: ma = re.match(r'\Aimooc[\w]*','iimooc')

In [57]: ma.group()
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-57-7c62fc675aee> in <module>()
----> 1 ma.group()

AttributeError: 'NoneType' object has no attribute 'group'

# 手机号匹配
result = re.match(r'1[35678]\d{9}$','15735177116')
 
 result
 <_sre.SRE_Match object; span=(0, 11), match='15735177116'>
 
 result.group()
 '15735177116'

五、分组匹配

字符	功能
|	匹配左右任意一个表达式
(ab)	将括号中字符作为一个分组
\num	引用分组num匹配到的字符串
(?P<name>)	分组起别名
(?P=name)	引用别名为name分组匹配到的字符串

分组匹配

In [59]: ma = re.match(r'abc|d','abc')

In [60]: ma.group()
Out[60]: 'abc'

In [61]: ma = re.match(r'abc|d','d')

In [62]: ma.group()
Out[62]: 'd'

In [63]: ma = re.match(r'[1-9]?\d$','9')

In [64]: ma.group()
Out[64]: '9'

In [65]: ma = re.match(r'[1-9]?\d$','99')

In [66]: ma.group()
Out[66]: '99'

In [67]: ma = re.match(r'[1-9]?\d$','09')

In [68]: ma

In [69]: ma = re.match(r'[1-9]?\d$','100')

In [70]: ma.group()
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-70-7c62fc675aee> in <module>()
----> 1 ma.group()

AttributeError: 'NoneType' object has no attribute 'group'

In [71]: ma = re.match(r'[1-9]?\d$|100','100')

In [72]: ma.group()
Out[72]: '100'

In [73]: ma = re.match(r'[1-9]?\d$|100','99')

In [74]: ma.group()
Out[74]: '99'

In [75]: ma = re.match(r'[\w]{4,6}@163.com','imooc@163.com')

In [76]: ma.group()
Out[76]: 'imooc@163.com'

In [77]: ma = re.match(r'[\w]{4,6}@(163,123).com','imooc@163.com')

In [78]: ma = re.match(r'[\w]{4,6}@(163,123).com','imooc@123.com')

In [79]: ma.group()
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-79-7c62fc675aee> in <module>()
----> 1 ma.group()

AttributeError: 'NoneType' object has no attribute 'group'

In [80]: ma = re.match(r'[\w]{4,6}@(163|123).com','imooc@123.com')

In [81]: ma.group()
Out[81]: 'imooc@123.com'

In [82]: ma = re.match(r'<[\w]+>','<book>')

In [83]: ma.group()
Out[83]: '<book>'

In [84]: ma = re.match(r'<([\w]+>)','<book>')

In [85]: ma.group()
Out[85]: '<book>'

In [86]: ma = re.match(r'<([\w]+>)\1','<book>')

In [87]: ma.groups()
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-87-f4e4ca66607d> in <module>()
----> 1 ma.groups()

AttributeError: 'NoneType' object has no attribute 'groups'

In [88]: ma = re.match(r'<([\w]+>)\1','<book>book>')

In [89]: ma.groups()
Out[89]: ('book>',)

In [90]: ma.group()
Out[90]: '<book>book>'

In [91]: ma = re.match(r'<([\w]+>\1','<book>book>')



In [3]: ma = re.match(r'<([\w]+>)[\w]+</\1','<book>python</book>')

In [4]: ma.group()
Out[4]: '<book>python</book>'

In [5]: ma = re.match(r'<([\w]+>)[\w]+</\1','<book>python</book1>')

In [6]: ma


In [9]: ma = re.match(r'<(?P<mark>[\w]+>)[\w]+</(?P=mark)','<book>python</book>')

In [10]: ma.group()
Out[10]: '<book>python</book>'

#   匹配邮箱
p = '(\w+)@(163|126|gmail|qq)\.(com|cn|net)$'
 
r = re.match(p,'zhang@qq.com')
 
 r
 <_sre.SRE_Match object; span=(0, 12), match='zhang@qq.com'>
 
 r.group()
 '# zhang@qq.com'

六、python贪婪和非贪婪

Python里数量词默认是贪婪的（在少数语言里也可能是默认非贪婪），总是尝试匹配尽可能多的字符；非贪婪则相反，总是尝试匹配尽可能少的字符。

在”*”,”?”,”+”,”{m,n}”后面加上？，使贪婪变成非贪婪。

s = 'this is a number 234-235-22-432'
r = re.match(r'.+(\d+-\d+-\d+-\d+)',s)
r.group(1)
Out[32]: '4-235-22-432'

咦？怎么和我们想的不一样啊？这就是因为Python默认的贪婪算法，解决方法：在*,+后面+？

r = re.match(r'(.+?)(\d+-\d+-\d+-\d+)',s)
r.groups()
Out[33]: ('this is a number ', '234-235-22-432')
r = re.match(r'(.+?)(\d+-\d+-\d+-\d+)',s)
r.group(1)
Out[34]: 'this is a number '
r = re.match(r'(.+?)(\d+-\d+-\d+-\d+)',s)
r.group(2)
Out[35]: '234-235-22-432'