Regular expression of Python

1, What is regular expression ？

Regular expressions （regular expression） Is an expression used to express a set of strings concisely .

2, What is the role ？

① The characteristics of expressing text types . ② Find or replace a set of strings at the same time . ③ Match all or part of a string .

3, Common operators ：

 

The operator	explain	Example
.	Represents any single character
[]	Character set , Give a value range for a single character	[abc] Express a,b,c,[a-z] Express a-z Single character
[^]	Non character set , Give the exclusion range for a single character	[^abc] Express Division a,b,c A single character other than
*	Previous character 0 Times or infinitely	abc* Express ab,abc,abcc,abccc wait
+	Previous character 1 Times or infinitely	abc+ Express abc,abcc,abccc wait
？	The previous character appears or does not appear	abc Express ab,abc
|	Any one of the left and right expressions	abc|def Express abc,def
{m}	Extend the previous character m Time	ab{4}c Express abbbbc
{m,n}	Extend the previous character m To n Time , contain m,n	ab{1,2}c Express abc,abbc
^	Match the beginning of a string	^abc Express abc And at the beginning of the string
$	Match string end	abc$ Express abc And at the end of the string
()	Group markers , The interior can only be used | The operator	（abc） Express abc,（abc | def） Express abe、def
\d	Numbers , Equivalent to [0,9]
\w	Word characters , Equivalent to [A-Za-z0-9_]

4, Some syntax examples of regular expressions

Regular expressions	The corresponding string
P(Y|YT|YTH|YTHO)?N	"PN","PYN","PYTN","PYTHN","PYTHON"
PYTHON+	"PYTHON","PYTHONN","PYTHONNN".......
PY[TH]ON	"PYTON","PYHON"
PY[^TH]?ON	"PYON","PYAON","PYBON","PYCON"......
PY{:3}N	"PN","PYN","PYYN","PYYYN"

5, Classic examples of regular expressions

^[A-Za-z]+$	from 26 A string of letters
^[A-Za-z0-9]+$	from 26 A string of letters and numbers
^-?\d+$	String in integer form
^[0-9]*[1-9][0-9]*$	A string in the form of a positive integer
[1-9]\d{5}	Postcode in China
[\u4e00-\u9fa5]	Match Chinese characters
\d{3}-\d{8}|\d{4}-\d{7}	Domestic phone number ,010-12345678
[1-9]?\d	0-99
1\d{2}	100-199
2[0-4]\d	200-249
25[0-5]	250-255
(([1-9]?\d|1\d{2}|2[0-4]\d|25[0-5]).){3}([1-9]?\d|1\d{2}|2[0-4]\d|25[0-5])	matching ip Address

6,re Basic use of Library

 

re The main functions of the library are

re.search()	Search a string for the first place to match a regular expression , return match object
re.match()	Match regular expressions from the beginning of a string , return match object
re.findall()	Search string , Return all matching substrings with list type
re.split()	Split a string according to the regular expression matching result , Return list type
re.finditer()	Search string , Returns the iteration type of a matching result , Each iteration element is match object
re.sub()	Replace all substrings matching regular expressions in a string , Return the replaced string

 

①search(pattern, string, flags=0)

pattern： The string or native string representation of a regular expression
string： String to match
flags： Control flags when regular expressions are used

import re
match = re.search(r"[1-9]\d{5}", "haha 723300")
if match:
print(match.group())

G:\Project1\venv\Scripts\python.exe G:/Project1/practice/lianxi2.py
723300

Process finished with exit code 0

②match(pattern,string,flags=0)

It should be noted that match The function starts at the beginning of a string , If the start doesn't match , No more searching for , If found, the return value is One match object , Return when you can't find it None

import re
match = re.match(r"[1-9]\d{5}", "haha 723300")
print(type(match))
match = re.match(r"[1-9]\d{5}", "723300 haha")
if match:
print(match.group())

G:\Project1\venv\Scripts\python.exe G:/Project1/practice/lianxi2.py
<class 'NoneType'>
723300

Process finished with exit code 0

so search And match The difference is that ：
match The substring to be matched must be at the beginning of the string , Otherwise, we can't find , and search There is no such requirement

③findall（pattern,string,flags=0）

import re
c = re.findall(r"[1-9]\d{5}", "haha723300 xixi612203")
print(type(c))
print(c)

G:\Project1\venv\Scripts\python.exe G:/Project1/practice/lianxi2.py
<class 'list'>
['723300', '612203']

Process finished with exit code 0

④split(pattern,string,maxsplit=0,flags=0)

maxsplit： Maximum number of divisions , The rest is output as the last element

import re
a = re.split(r"[1-9]\d{5}", "haha723300 xixi612203")
print(type(a))
print(a)

a = re.split(r"[1-9]\d{5}", "haha723300 xixi612203", maxsplit=1)
print(a)

str1 = "name: hpl, age: 18"
b = re.split(r'\:|\,', str1)
print(b)


G:\Project1\venv\Scripts\python.exe G:/Project1/practice/lianxi2.py
<class 'list'>
['haha', ' xixi', '']
['haha', ' xixi612203']
['name', ' hpl', ' age', ' 18']

Process finished with exit code 0

⑤finditer(pattern,string,flags=0)

import re
for m in re.finditer(r"[1-9]\d{5}", "haha723300 xixi612203"):
if m:
print(m.group())

G:\Project1\venv\Scripts\python.exe G:/Project1/practice/lianxi2.py
723300
612203

Process finished with exit code 0

⑥sub(pattern,repl,string,count=0,flags=0)

repl： Replace string matching string
count： The maximum number of replacements to match

import re
m = re.sub(r"[1-9]\d{5}", "love", "haha723300 xixi612203")
if m:
print(m)

G:\Project1\venv\Scripts\python.exe G:/Project1/practice/lianxi2.py
hahalove xixilove

Process finished with exit code 0

7,re Library match object

attribute ：
string The text to be matched
re Used when matching pattern object （ Regular expressions ）
pos The beginning of regular expression search text
endpos The end of regular expression search text

Method ：
group() Get the matching string
start() Match string at the beginning of the original string
end() Match string at the end of the original string
span() return （start）…（end）

import re
match = re.search(r"[1-9]\d{5}", "haha723300 xixi612203")
print(match.string)
print(match.re)
print(match.pos)
print(match.endpos)
print(match.group())
print(match.start())
print(match.end())
print(match.span())

G:\Project1\venv\Scripts\python.exe G:/Project1/practice/lianxi2.py
haha723300 xixi612203
re.compile('[1-9]\\d{5}')
0
21
723300
4
10
(4, 10)

Process finished with exit code 0

8,re Library Greedy matching and minimum matching

①re The library defaults to greedy matching , That is, the output matches the longest substring

import re
match = re.search(r'PY.*N','PYANBNCNDN')
print(match.group())

G:\Project1\venv\Scripts\python.exe G:/Project1/practice/lianxi2.py
PYANBNCNDN

Process finished with exit code 0

② The method of minimum matching ： Add... After the extension operator ？

Minimum match operator

The operator	explain
*？	Previous character 0 Times or infinitely , Minimum match
+？	Previous character 1 Times or infinitely , Minimum match
？？	Previous character 0 Time or 1 Second expansion , Minimum match
[m,n]?	Extend the previous character m to n Time ( contain n), Minimum match

import re
match = re.search(r'PY.*?N','PYANBNCNDN')
print(match.group())

G:\Project1\venv\Scripts\python.exe G:/Project1/practice/lianxi2.py
PYAN

Process finished with exit code 0