Python Program to Check the Strength of Password

Last Updated on 28 April 2025

It is very important to secure our online accounts with a strong password. A weak password can make our accounts more vulnerable and easier to access. In this article, we will learn how to create a simple Python program to check the strength of a password.

We will use the re module in Python, which allows us to work with regular expressions. Regular expressions help us match patterns in a string, a good choice for validating passwords.

Let’s get started!

Important Points to Remember

Passwords must be at least 10 characters long and must include:

• At least one lowercase letter (a-z)
• At least one uppercase letter (A-Z)
• At least one number (0-9)
• At least one special character (@#$%^&+=!)

Remember, a strong password is harder to guess or crack.

Python Code to Check Password Strength

Here is the complete code to check if a password is strong:

import re

check_pass = re.compile(r'''(
^.*(?=.{10,})           # Checking the length, minimum 10 characters
(?=.*\d)                # At least one Numeric Digit
(?=.*[a-z])             # At least one Lowercase letter (a to z)
(?=.*[A-Z])             # At least one Uppercase letter (A to Z)
(?=.*[@#$%^&+=!]).*$    # At least one Special Character
)''', re.VERBOSE)

passCode = input('Enter the Password: ')
mo1 = check_pass.search(passCode)

# Check if the password is valid or not
if mo1:
    print("Strong Password.")
else:
    print("Not Valid! Weak Password.")

Output

Enter the Password: GoogleGoogleHappyBirthday@23
Strong Password.

Enter the Password: password123
Not Valid! Weak Password.

Line-by-Line Explanation of the Code

Let’s understand how the program works, especially the regular expression (regex) part:

Import the re module

import re

re is Python’s built-in library for working with regular expressions.

Compile the password checking pattern

check_pass = re.compile(r'''(...)''', re.VERBOSE)

Here:

• We create a regular expression pattern inside re.compile.
• re.VERBOSE allows us to write the regex in a readable, multi-line format with comments.

Inside the Regular Expression:

^.*(?=.{10,})

• ^ means the start of the string.
• .* means any character (0 or more times).
• (?=.{10,}) ensures that the password has at least 10 characters

(?=.*\d)

• \d matches any digit (0-9).
• This checks that the password has at least one number.

(?=.*[a-z])

• Matches at least one lowercase letter (from a to z).

(?=.*[A-Z])

• Matches at least one uppercase letter (from A to Z).

(?=.*[@#$%^&+=!])

• Checks for at least one special character like @, #, $, %, ^, &, +, =, !.

.*$

• .* means any character.
• $ marks the end of the string.