Introduction

The task is to check whether the given password is strong or not using regular expression.

Requirements for strong password:

• The password must be 8 to 15 characters long.
• The password must contain at least one lowercase, uppercase alphabet, digit, and a special character.
• The password must not contain a newline or space in between the string.
• Same character must not be repeated more than 3 times.
• There must not be the repetition of string pattern.

Program

import re 
def check(pwd): 
    if pwd == "\n" or pwd == " ": 
        return "Password must not contain a newline or space!"
 
    if 8 <= len(pwd) <= 15: 
        if not re.search('[a-z]', pwd):
            print("Weak Password! At least one lowercase alphabet should be present!")
        elif not re.search('[A-Z]', pwd): 
            print("Weak Password! At least one uppercase alphabet should be present!") 
        elif not re.search('[0-9]', pwd): 
            print("Weak Password! At least one digit should be present!")
        elif not re.search('[_@$]', pwd): 
            print("Weak Password! At least one special char should be present!")
        elif re.search(r'(.)\1\1\1', pwd): 
            print("Weak Password! Char repetition more than 3 times!")
        elif re.search(r'(..)(.*?)\1', pwd): 
            print("Weak Password! String pattern repetition!")
        else: 
            print("The given password is a strong password!")
   
    else: 
        print("Weak Password! Password must be 8 to 15 characters long! ")
        
ip_str = input("Enter the string: ")
check(ip_str)

Output

Explanation

In the above python code, we have checked the conditions for strong password using re.search() method in if-elif condition. If all the conditions are satisfied, the given password is strong. In case any of the condition fails, the password is weak.