Introduction to the re module and regular expressions in python (with code)

This article brings you an introduction to the re module and regular expressions in Python (with code). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

Regular expression (English: Regular Expression, often abbreviated as regex, regexp or RE in code), also known as regular expression, regular expression, regular expression, regular expression, regular expression, is A concept in computer science. Regular expressions use a single string to describe and match a series of strings that match a certain syntax rule. In many text editors, regular expressions are often used to retrieve and replace text that matches a certain pattern.

Regular expression rules, single character matching

##.Match any character (except n)b.bbab,b2b[ ] Matches any character from the character set in [] i [abCde]mi am\d Matches any decimal digit, consistent with [0-9]w\dcschoolw3cschool\Dmatches non-numbers, that is, not numbersmou\Dhmouth\s Matches any space character, same as [\n\t\r\v\f]i\slikei like \S Matches any non-whitespace character, as opposed to \sn\Senoe,n3e\w Matches any alphanumeric character, same as [A-Za-z0-9_][A-Za-z]w ##\W means the quantity matches

Character	Function	Regular expression example	Match matching example
Matches non-word characters	[0-9]\W[A-Z]	3 A

characters ##* Matches the previous regular expression 0 or more times, optionala*aaa Matches the previous character once or infinitely, that is, at least once a aaa? Matches the previous character appearing 1 or 0 times, either once or not a?a or b Matches the previous character m times Match the previous character appearing at least m timesmatches the previous one Characters appear from m to n times a{2,6}aaa

function	regular expression example	matching example
				##{m}
[0-9]{5 }	12345			{m.}
a{5.}	aaaaa			##{m,n}
				Represents boundary matching

Characters

FunctionRegular expression example^Match the beginning part of the string^Dear$Match the ending part of the stringfi$bMatch any word boundary\bThe\bBMatch non-word boundaries.*\Bver\##Match groupsCharacter

Functionmatches either left or right The expression ##(ab) treats the characters in brackets as a group\numReference the string matched by group num(?P< ;name>)Group alias(?P=name)The reference alias is name Group matched stringsCommon functions and methods of re module

		##\
	re module	In python, you can use the built-in re module Regular expression

Core function

Description

compile(pattern,flags=0)	Compiles the regular expression pattern using any optional flags, then returns a regular expression object

##sub(pattern,repl,string,count=0) Use repl to replace all occurrences of the regular expression pattern in the string. Unless count is defined, all occurrences will be replaced.

re module functions and regular expression object methods	Description
match(pattern, string,flags=0)	Attempts to match a string using a regular expression pattern with optional flags. If the match is successful, return the matching object; if it fails, return None
search(pattern,string,flags=0)	Search for string using optional flags The first occurrence of the regular expression pattern in . If the match is successful, the matching object is returned; if it fails, None is returned.
findall(pattern,string,[,flags])	Find all occurrences in the string regular expression and returns a list
split(pattern,string,max=0)	According to the pattern separator of the regular expression, the split function separates the characters Split the string into a list, and then return a list of successful matches. The split operation can be max times (the default is to split all successfully matched positions)

Commonly used matching object methodsDescription##group(num=0)groups(default=None)span()

Default returns the entire matching object or returns a specific subgroup numbered num
Returns a tuple containing all matching subgroups, If there is no successful match, an empty tuple is returned

Commonly used module attributes, most of which are used to modify regular expression functionsre .Ire.S##re.MMulti-line matching, affecting ^ and $re.UParses characters according to the Unicode character set. Affects \w, \W, \b and \Bre.X This flag makes it easier to write regular expressions by giving you more flexible formatting Understand the general usage of re module

Explanation
Make the match case-insensitive (ignore case)
.(dot) matches anything except n All characters except, re.S mark indicates. (dot) can match all characters

Use the

compile()
1. function to convert the regular expression The string form is compiled into a regular expression object;
   matches the text through a series of methods provided by the regular expression object (such as:
match()
2. ) Search and obtain the matching result, a

   Match object;

   Finally use the properties and methods provided by the
Match
3. object (for example:

   group ()) Obtain information and perform other operations as needed.

   re module usage example

Import module

import re

compile()

Function compile function is used to compile regular expressions and generate a Pattern object. Its general usage form is as follows:

import re

# 将正则表达式编译成pattern对象
pattern = re.compile(r'\d+')

After compiling into a regular expression object, you can use the regular expression mentioned above expression object method.

match()

Method The match method is used to find the head of the string (you can also specify the starting position), it is once Matching, as long as a matching result is found, it is returned instead of searching for all matching results. Its general usage form is as follows:

match(string[, pos[, endpos]])

Among them, string is the string to be matched, pos and endpos are optional parameters, specifying the start and

endpoint# of the string. ## position, the default values ​​are 0 and len (string length) respectively. Therefore, when you do not specify pos and endpos, the match method defaults to matching the head of the string. When the match is successful, a Match object is returned. If there is no match, None is returned. <pre class="brush:php;toolbar:false">&gt;&gt;&gt; import re &gt;&gt;&gt;  &gt;&gt;&gt; pattern = re.compile(r'\d+') # 正则表达式表示匹配至少一个数字 &gt;&gt;&gt;  &gt;&gt;&gt; m = pattern.match(&quot;one2three4&quot;) # match默认从开头开始匹配，开头是字母o，所以没有匹配成功 &gt;&gt;&gt; print(m) # 匹配失败返回None None &gt;&gt;&gt;  &gt;&gt;&gt; m = pattern.match(&quot;1two3four&quot;) # 开头字符是数字，匹配成功 &gt;&gt;&gt; print(m) &lt;_sre.SRE_Match object; span=(0, 1), match=&amp;#39;1&amp;#39;&gt; &gt;&gt;&gt;  &gt;&gt;&gt; m.group() # group()方法获取匹配成功的字符 '1' &gt;&gt;&gt; m = pattern.match(&quot;onetwo3four56&quot;,6,12) # 指定match从数字3开始查找，第一个是数字3，匹配成功 &gt;&gt;&gt; print(m) &lt;_sre.SRE_Match object; span=(6, 7), match=&amp;#39;3&amp;#39;&gt; &gt;&gt;&gt; m.group() '3'</pre>

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