Detailed explanation of re regular module in python

1. Common symbols of regular expressions

'.'     默认匹配除\n之外的任意一个字符，若指定flag DOTALL,则匹配任意字符，包括换行
'^'     匹配字符开头，若指定flags MULTILINE,这种也可以匹配上(r"^a","\nabc\neee",flags=re.MULTILINE)
'$'     匹配字符结尾，或e.search("foo$","bfoo\nsdfsf",flags=re.MULTILINE).group()也可以
'*'     匹配*号前的字符0次或多次，re.findall("ab*","cabb3abcbbac")  结果为['abb', 'ab', 'a']
'+'     匹配前一个字符1次或多次，re.findall("ab+","ab+cd+abb+bba") 结果['ab', 'abb']
'?'     匹配前一个字符1次或0次
'{m}'   匹配前一个字符m次
'{n,m}' 匹配前一个字符n到m次，re.findall("ab{1,3}","abb abc abbcbbb") 结果'abb', 'ab', 'abb']
'|'     匹配|左或|右的字符，re.search("abc|ABC","ABCBabcCD").group() 结果'ABC'
'(...)' 分组匹配，re.search("(abc){2}a(123|456)c", "abcabca456c").group() 结果 abcabca456c
 
 
'\A'    只从字符开头匹配，re.search("\Aabc","alexabc") 是匹配不到的
'\Z'    匹配字符结尾，同$
'\d'    匹配数字0-9
'\D'    匹配非数字
'\w'    匹配[A-Za-z0-9]
'\W'    匹配非[A-Za-z0-9]
's'     匹配空白字符、\t、\n、\r , re.search("\s+","ab\tc1\n3").group() 结果 '\t'

　

2. Common syntax

2.1 re.match matches from scratch

re.mathch(pattern,string,flags)

• The first parameter is the regular expression Formula, here is "(\w+)\s", if the match is successful, a Match is returned, otherwise a None is returned;

• The second parameter represents the string to be matched;

• The third parameter is the Peugeot bit, which is used to control the matching method of the regular expression, such as: whether it is case-sensitive, multi-line matching, etc.

#匹配开头成功
>>> a=re.match("i",'inet 172.17.0.1  netmask 255.255.0.0  broadcast 0.0.0.0')
>>> a.group()
'i'

# 匹配开头失败
>>> a=re.match("n",'inet 172.17.0.1  netmask 255.255.0.0  broadcast 0.0.0.0')
>>> a.group()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: &#39;NoneType&#39; object has no attribute &#39;group&#39;
>>> print(a)
None

#\w匹配 (不匹配特殊字符 空格等)
>>> a=re.match("\w{4,10}",&#39;inet 172.17.0.1  netmask 255.255.0.0  broadcast 0.0.0.0&#39;)
>>> a.group()
&#39;inet&#39;

　

2.2 re.search

The re.search function will search for pattern matching within the string, only Returns the first match found, or None if the string does not match.

>>> a=re.search("\d+","sd234345resss")
>>> a.group()
'234345'

　

2.3 group and groups

>>> a=re.search("([a-z]*)(\d+)([a-z]*)","sd234345resss").group()
>>> a
'sd234345resss'
>>> a=re.search("([a-z]*)(\d+)([a-z]*)","sd234345resss").group(0)
>>> a
'sd234345resss'
>>> a=re.search("([a-z]*)(\d+)([a-z]*)","sd234345resss").group(1)
>>> a
'sd'
>>> a=re.search("([a-z]*)(\d+)([a-z]*)","sd234345resss").group(2)
>>> a
'234345'
>>> a=re.search("([a-z]*)(\d+)([a-z]*)","sd234345resss").group(3)
>>> a
'resss'
>>> a=re.search("([a-z]*)(\d+)([a-z]*)","sd234345resss").groups()
>>> a
('sd', '234345', 'resss')

　

2.4 re.findall(pattern,string,flags=0)

The above two methods are used to match single values, that is: they can only match strings One of them, if you want to match all elements in the string that meet the conditions, you need to use findall.

>>> a=re.findall("\d+","sd234/34*5resss")
>>> a
['234', '34', '5']

　

2.5 re.sub(pattern,repl,string,count=0,flags=0)

Replace the matched string

>>> s="123abc456"
>>> a=re.sub("\d+","SUB",s)
>>> a
'SUBabcSUB'

More powerful than str.replace

2.6 re.split(pattern, string, maxsplit=0, flags=0)

Group according to the specified match

s="123aaa345bbb789ccc"
>>> a=re.split("[a-z]*",s)
>>> a
['123', '345', '789', '']
>>> a=re.split("[a-z]*",s,1)
>>> a
['123', '345bbb789ccc']
>>> a=re.split("[a-z]*",s,2)
>>> a
['123', '345', '789ccc']

　

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