Regular expressions in Python

1. Re.match function

Re.match tries to match a pattern from the beginning of the string, if it is not successful at the starting position. Match () will return none

Syntax: Re.match (pattern,string,flags=0)

Pattern: Regular expression to match

String: Target string

Flags: Used to control how expressions are matched, such as: case sensitivity, multiline matching, and so on.

Print (Re.match ('www','www.ruboob.com'3)# match at start position Print (Re.match ('com','www.ruboo.com') None  # does not match at start position

2. Group () function to get the matching expression

 >>> line =  " cats is smarter than dogs   " >>> p = re.match (R"   (. *). *   "  >>> P  <_sre. Sre_match object; span= (0, Match=
     
     cats is smarter than dogs  
      " >>>>
      P.group ()  
      " 
     cats is smarter than dogs  
     "  >>> P.group (1
        cats   " 
    

3. Re.search function

Re.search scans the entire string and returns the first successful match.

Syntax: Re.search (pattern,string,flags)

4, the difference between re.search&re.match

Re.match matches only the beginning of the string, if the string does not begin to conform to the regular expression, the match fails and the function returns none;

Re.search matches the entire string until a match is found.

5. Search and replace

Python's re module provides a match for re.sub to replace a string

Syntax: Re.sub (pattern,repl,string,count=0,flags=0)

A special mark for marking special information.

Parameters:

Pattern: Patterns string in regular

REPL: The replacement string, or as a function

String: The strings to be looked up

Count: The maximum number of times a pattern match is replaced, and the default of 0 means that all matches are replaced

>>> phone ='2004-959-559 # This is a foreign phone number'>>> num = re.sub (r'#.+',"', phone)#Remove Chinese comments>>>Num'2004-959-559'>>> num = re.sub (r'\d',"', phone)#Remove the small horizontal bar>>>Num'2004959559'

REPL is a function

 import   re  #   Multiply the matched number by 2  def   double (matched): value  = Int (Matched.group ( "  value   "  )  return  str (value * 2) s  =  " a23g4hfd567    print  (re.sub ( '   (? p<value>\d+)   " , double, s))  Span style= "COLOR: #008000" >#   result  a46g8hfd1134 

Regular expressions in Python