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Built-In Functions In Regex

Basic Of Function of Regular Expression

For searching pattern, there are following two ways

1.single First match

  • re.search() to find the first match for a pattern.

2.Multiple Match

  • re.findall() finds all the matches and returns them as a list of strings, with each string representing one match.

1.search

  • The re.search() method takes a regular expression pattern and a string and searches for that pattern within the string.
  • This will return a match object if the search is successful Otherwise return None.
  • re.search() return the only first occurrence of searching pattern in the input given string.
  • add 'r' before the searching pattern which will be considered as a raw string

group():

  • group() is a method for an instance of the match object.
  • Return str or tuple,
  • Return subgroup(s) of the match by indices or names

Syntax:

re.search(pattern,string)

Example 1:

problem: find out 're' in a given string

import re
text='''this is simple re python program.re 
is a short form of regular expression'''
pattern=r're'

search_result=re.search(pattern,text)

#Get Type of result
print(type(search_result))

#Result:<class '_sre.SRE_Match'>
#use match object to get the result
if search_result:
    print('Result is found for :'+search_result.group())
else:
    print('Not Found')

OutPut:

<class '_sre.SRE_Match'>
Result is found for :re

2.findall

  • find all is used to get the multiple occurrences of a given pattern.
  • The findall() function returns a list containing all matches.
  • The list contains the matches in the order they are found. If no matches are found, an empty list is returned.

Syntax:

re.findall(pattern,string)

Example: Find out all occurrences of 're'

#import Required module
import re

#String
input_string='''this is simple re python program.re
is a short form of regular expression'''

#pattern 
pattern='re'

result=re.findall(pattern,input_string)
print(result)

Output:

['re', 're', 're', 're']

3.split()

  • Returns a list where the string has been split at each match.
  • The split() function returns a list where the string has been split at each match.
  • If multiple patterns matching in the split() function the list is split accordingly pattern.
input_string:'python'
splited list:['p', 'thon']

Syntax:

re.split('pattern',input_string)

Example:

#import Module
import re

#input String
str = "This is python program"

#Result
result = re.split("python", str)
print(result)

Output:

['This is ', ' program']

4.sub()

  • Replaces one or many matches with a given input string

consider

input_string :'python'
pattern      : 'py'
replace Text : 'cy'
result of re.sub(): 'cython'

Syntax:

re.sub('Search pattern','replace Text',input_string)

Example:

#import Module
import re

#input String
input_string = "This is python program"

#replace 'i' with 'it' word in given input_string
result = re.sub('i',"It", input_string)
print(result)

Output:

ThIts Its python program