regular expression

Regular expressions

regular expression

Regular expressions are a text pattern , Include normal characters （ for example ,a To z Between the letters ） And special characters （ be called " Metacharacters "）.

Regular expressions are described using a single string 、 Match a string that matches a syntax rule .

**re Module USES

lookup

search	 # Only return one 
match 	 # Only return one , Only those that match from the beginning are counted 
findall 	# Return string 
finditer	 # return Match iterator 

search,match All of them Match object 
m.group()	 Display the data 
m.group(1)	 Show first group 
m.groups()   Show all groups  （1,2,3） Group 

findall Return result array 

Replace

sub     # Replace 
subn	# After replacement , How much is replaced 

re.sub(r'123','456',text)
 Return the replaced string 

re.subn(r'123','456',text)
 Return the replaced string , And replaced a few places 

Division

split
 What segmentation is used for regular representation , Return the result list of segmentation 
 Example 

text='sassas , sas ; sas'
re.split(r'\s*[,.;]\s*',text) # Multiple spaces [,.;] Multiple spaces 
 return ['sassas', 'sas', 'sas']

** Rule of grammar

Character category

matching	Regular
a,b,c,1,2,3	Constant , Write what is what
\d	A number
\D	A non numeric character
\s	A space
\S	A non space
\w	An arbitrary alphanumeric underline
[abc]	a,b,c Any character
[a-e]	a To e Any one of
[^a-d]	Take the opposite , except a,b,c,d Any one of
[\d]	Back space （Backspace）
.	Wildcard Division \n Any character outside

quantifiers （ frequency ）

Regular	matching
*	0 Or more
+	1 Or more
？	0 or 1 individual
{2}	2 individual
{2,5}	2 To 5
{2,}	least 2
{,4}	most 4

Portfolio model

Multiple pattern combinations

\d{
    6}[a-z]{
    6}   # Six numbers ,6 individual a-z

|	# Both modes are OK , Such as two numbers or two characters  \d{2}|\w{2}


# grouping , After grouping, you can use quantifiers in groups 
()			# Such as （122）{3}  matching 3 Time 122

Location

Regular	matching
^	Start of string
\A	Start of string , Ignore m Mark
$	End of string
\Z	End of string , Ignore m Mark
\b	At the word boundary
\B	Not at word boundaries
(?<=xxx)\d	matching xxx after Of A number
(?=xxx)\d	matching xxx The first number at the beginning
(?!XXX)\d	Matching is not xxx At the beginning A number

grouping

It's too complicated to annotate

r'(sa)(?# What does the front match )'

Regular	matching
（…）	A group
（？P）	Group name is Y Group
（?：…）	Do not capture groups
\Y	Matching first Y Matching groups
（？P=Y）	The matching name is Y Group
（？#）	notes

Mark

re=re.findall(r'sad',flag=re.I)

Regular	matching
i	Ignore case
m	^ and $ Match the beginning and end of a line
s	. Match newline
x	Allow spaces and comments
\u	Unicode matching

Replace

Regular	matching
\g<0>	Insert the whole segment to match
\g	Insert matching Y,Y It can be a matching name or number
\Y	Insert, Y Group

string matching

import re

# Fixed string 
re.findall(r'123455',text)
      
 r Express raw, Native string 
      
# A certain category 
re.findall(r'\d',text)

\d \d+  
 Decorate the preceding characters # Such as  \d Match a number ,\d{4} Match four 


# Combination match 

re.findall(r'\d{2}abc\d{5}',text)


# Multiple situations ,
| The division , look for 123 or 456
re.findall(r'123|345')

# Limit position 
	^ Starting position 
	$ End position 

# Internal constraints 
w character ,（） Means a group ,（\1） It means the same as the first group 

text='abcabc5613111111'
re.findall(r'(\w{3})(\1)',text)
 return [('abc','abc'),('111','111')]

Writing steps

• 1. Find matching characters

  • Find the right model according to your needs
  • Use the lookup function

• 2. Split string

  • Observe the split pattern of the split string
  • split function

• 3. Replace

  • Find the right model according to your needs
  • Use the substitution function