Problem Statement: To understand Python RegEx.

RegEx stands for Regular Expression. The Regex or Regular Expression is a way to define a pattern for searching a string or a set of strings. 

The re module  

Python contains a built-in module (re) that provides all the required functionality needed and supports the  RegEx.

Syntax:  import re

Python regex module consists of multiple methods. Some of them are explained below.

Regex Metacharacters

The special characters used in RegEx are known as metacharacters.

For example, characters like ‘|’, ‘+’, or ‘*’.

Some of the metacharacters are :

Regex special sequences

A special sequence consists of  “\” and some selected characters. Every special sequence has a unique meaning.

Let us see some of the special sequences.

Regex flags

RE module methods have an optional flags argument which is used to enable various unique features. Let us see some of the flags.

 Let us see some of the advantages of regular expressions.

• It helps us in searching and replacing text in files. 
• Validating text input, such as password and email address.
• Rename a hundred files at any given time.

Example1:

Let us take an example

Program to check whether the given email is valid or not. Where email ends with com, in, net only.

Solution:

import re
 
patt = "[a-zA-Z0-9]+@[a-zA-Z]+\.(com|net|in)"
 
def isValid(email):    
    if re.search(patt, email):
        print("Email is valid")
    else:
        print("Email is Invalid ")
 
 
isValid("[email protected]")
isValid("tak[email protected]")
isValid("[email protected]")
isValid("[email protected]")

Example2:

We have given some employees id’s of company XYZ. Employee id consists of five to seven characters, which are separated into two parts by a space. The first half consists of two to four characters and the other half consists of three characters. The first half consists of a digit followed by one or two uppercase characters and the other half has two uppercase characters, followed by a digit.

Eg : AB1 2CD, AB2C 1WA.

 Write a regex to find if the given employee id belongs to company XYZ or not.

Disclaimer: Don’t jump directly to the solution, try it out yourself first.

Solution :

We will try to make a pattern according to the given question

[A-z]{1,2}[0-9R][0-9A-Z] ? [0-9][A-Z]{2}                  …. (pattern)

Code:

import re
 
employee_id = [  "AB1 0AA", 
                 "AZ1A 1AA", 
                 "SW1A 2BA", 
                 "BX3 2BB", 
                 "DH98 1BT", 
                 "N1 9UU", 
                 "EEZ3 1TT", 
                 "TIM E52", 
                 "A B1 A22", 
                 "AB34 2DD", 
                 "SE9 2HG", 
                 "N1 11H", 
                 "AC1V 8DS", 
                 "WCC1 9DD", 
                 "B4C 1LK", 
                 "B28 9AD", 
                 "WE12 7RJ", 
                 "AABB 007", 
                ]
patt = r"[A-z]{1,2}[0-9R][0-9A-Z]? [0-9][A-Z]{2}"
 
for Eid in employee_id:
    r = re.search(patt, Eid)
    if r:
        print(Eid + " is employee of XYZ")
    else:
        print(Eid + " is not an employee of XYZ")

Special thanks to AYUSH KUMAR for contributing to this article on takeUforward. If you also wish to share your knowledge with the takeUforward fam, please check out this article. If you want to suggest any improvement/correction in this article please mail us at [email protected]