Using Regex

Introduction

import re

def find(pattern, text):
    match = re.search(pattern, text)
    if match: return match.group()
    else: print("Match not Found")

pattern = "igs"
text = "called piiig"
find(pattern, text)

Match not Found

find("iig", "called piiig")

'iig'

find("...g", "called piiig")

'iiig'

find("...g", "called pimig")

'imig'

Repeating characters

• regex+ - one or more repetitions of preceding element
• regex* - zero or more repetitions of preceding element
• regex? – zero or one repetition of preceding element
• regex{n} - exactly n repetitions of preceding element
• regex{n,m} - from n to m repetitions of preceding element
• regex{n,} - n or more repetitions of preceding element

In Python you can use (.)\1{9,}

• (.) makes group from one char (any char)
• \1{9,} matches nine or more characters from 1st group

find(r"(.)\1{2}g", "called piiig")  #\1 - refers to first group. () indicates the group

'iiig'

find(r"(.)\1{2}g", "called piig")

Match not Found

find(r"(.)\1{2}g", "called psssg")

'sssg'

find(r"(.)\1{2}g", "called pssssg")

'sssg'

find(r"(.)\1{1,}g", "called pssssg")

'ssssg'

find(r"(.)\1{1,}g", "called pssg")

'ssg'

find(r"(.)\1{1,}g", "called psg")

Match not Found

Finding Email

find(r"[\w.]+@[\w.]+", "My email is foo@bar blah blah rahul.sarafiitk@gmail.com") # How to ensure atleast 1 . in second word

'foo@bar'

find(r"[\w.]+@[\w.]+", "My email is rahul.sarafiitk@gmail.com blah blah foo@bar")

'rahul.sarafiitk@gmail.com'