05 regular expression syntax

One 、 Regular expression common Syntax




. ： Is any character except newline a.c —> You can talk to abc matching 、acc matching 、a$c matching
****： It's the escape sign ,a.c–>a.c a\c—>a\c
[…]： Indicates that any character appears only once

\d： Is the match 0–9 One of the numbers
\D： Match non numeric , As long as it's not a number
\s： It is used to match white space a\sc–> a c
\S： It is used to match non blank characters a\Sc–>abc
\w： Match all the letters （ Include case ） Numbers and underscores and Chinese
\W： As long as it's not a letter （ Include case ） Numbers and underscores and Chinese , Everything else can match
** * *： Indicates the occurrence of the previous character 0 Times or times \d
+： Indicates that the previous character appears one or more times （ At least there must be 1 Time ）
？： Express Match the previous character 0 Time or 1 Time . Can only match to the front 1 individual
{m}： Match the previous character m Time

# 1、 Import the regular module 
import re

# 2、 Character matching 
#  One 、 Simple string matching 
rs = re.findall('abc', 'abc')  #  The first one is regular expression , Next is the string we are looking for 
print(rs)  # ['abc']
rs = re.findall('abc', 'abcfeffevfefggh')  #  Find the content we need from the following string 
print(rs)  # ['abc']

#  Two 、 Use “.” Match  (. Is to match any character except newline , Just can't match newline )
rs = re.findall('a.c', 'abc')
print(rs)  # ['abc']
rs = re.findall('a.c', 'a%c')
print(rs)  # ['a%c']
rs = re.findall('a.c', 'a\nc')
print(rs)  # []  Just can't match newline 
rs = re.findall('a\.c', 'a.c')  #  Only match a.c
print(rs)  # ['a.c']
rs = re.findall('a\.c', 'abc')  #  Only match a.c
print(rs)  # []  Only match a.c

#  3、 ... and 、 Use “[]” Match 
rs = re.findall('a[bc]d', 'abd')
print(rs)  # ['abd']
rs = re.findall('a[bc]d', 'acd')
print(rs)  # ['acd']
rs = re.findall('a[bc]d', 'aed')
print(rs)  # []  Only match abd、abc

#  Four 、 Predefined character set 
rs = re.findall('\d', '123')
print(rs)  # ['1', '2', '3']
rs = re.findall('\w', '123_ chinese ')
print(rs)  # ['1', '2', '3', '_', ' in ', ' writing ']
rs = re.findall('\w', '123_ chinese $')
print(rs)  # ['1', '2', '3', '_', ' in ', ' writing ']  Mismatch $ Symbol 
rs = re.findall('\W', '123_ chinese $')
print(rs)  # ['$']

#  5、 ... and 、 quantifiers 
rs = re.findall('\d*', '123')  #  Empty strings are allowed 
print(rs)  # ['123', '']
rs = re.findall('a\d*', 'a123')
print(rs)  # ['a123']
rs = re.findall('\d+', '123')
print(rs)  # ['123']
rs = re.findall('a\d?', 'a123')
print(rs)  # ['a1']
rs = re.findall('a\d{2}', 'a123')
print(rs)  # ['a12']

Two 、findall() Method


flag It's for the right . and \n Matching

import re

# 1.findall Method , Return a list of matching results 
rs = re.findall('\d+', 'chuan13zhi24')
print(rs)


# 2.findall In the method ,flag The role of 
rs = re.findall('a.bc', 'a\nbc')  # . Cannot match newline 
print(rs)  # []
#  If you want to . It can match the newline character , We need to use flag This parameter .re.DOTALL perhaps re.S  such , You can match all characters 
rs = re.findall('a.bc', 'a\nbc', re.DOTALL)
print(rs)   # ['a\nbc']
rs = re.findall('a.bc', 'a\nbc', re.S)
print(rs)   # ['a\nbc']


# 3.findall Method , Grouping is existence （）
'''  About the use of grouping in regularity , If there is no grouping , It is to use the whole regular string to find the content that matches this regular , Then go back .  however , If this findall Regular expressions in methods have groupings , That is, if there are parentheses , Then it will only return the content that matches the rule in the parentheses , Will return , such as ： a(.+)bc, Only returned \n. Other regularities are used for positioning . Only here a hinder ,bc Previous content , We don't want any other places  '''

#  No grouping , Then match from the whole string 
rs = re.findall('a.+bc', 'a\nbc', re.S)
print(rs)   # ['a\nbc']


#  This is grouping ( There are parentheses ), Only look for a hinder b Previous content ,a and b It's for positioning 
rs = re.findall('a(.+)bc', 'a\nbc', re.S)
print(rs)     # ['a\nbc']

3、 ... and 、r Use in the original string

import re
'''re The role of ：  There are several \ Just a few \, In this way, it is very simple for us to write regular expressions  '''

# 1、 Without using r When the original string , Encountered escape character (\) How do you do it? 

rs=re.findall('a\nbc','a\nbc')
print(rs)

rs=re.findall('a\\nbc','a\\nbc')
print(rs)

rs=re.findall('a\\\nbc','a\\nbc')
print(rs)

rs=re.findall('a\\\\nbc','a\\nbc')
print(rs)   # ['a\\nbc']  Need to write 4 Escape characters 

# r The original string in the regular can eliminate the influence of escape characters 
rs=re.findall(r'a\\nbc','a\\nbc')
print(rs)   # ['a\\nbc']

rs=re.findall(r'a\nbc','a\nbc')
print(rs)   # ['a\nbc']

#  Expand ： It can solve the problem of writing regular , Do not conform to the PEP8 The problem of specification ( No, r It's OK )
rs=re.findall(r'\d','a123')
print(rs)   # ['1', '2', '3']