How to Validate Passwords in Python?

In this tutorial, I will explain how to validate passwords in Python. As a Python developer working on a project for one of our USA clients, I came across a scenario where I needed to validate passwords when dealing with user registration to make the application more secure. I will help you to learn different methods to validate passwords effectively with examples.

Table of Contents:

Methods to Validate Passwords in Python

In this article, we’ll explore various methods to check if a given string is a valid password in Python.

Method 1: Use Regular Expressions

One effective way to validate passwords in Python is by using regular expressions (regex). Regex allows you to define a pattern that the password must match. Here’s an example:

import re

def validate_password(password):
    pattern = "^(?=.*?[A-Z])(?=.*?[a-z])(?=.*?[0-9])(?=.*?[#?!@$%^&*-]).{8,}$"
    return re.match(pattern, password) is not None
print(validate_password("Passw0rd!"))

Output:

True

I have executed the above example code and added the screenshot below.

This code uses a function that checks if a given password satisfies certain conditions defined by the regex pattern:

(?=.*?[A-Z]): At least one uppercase letter
(?=.*?[a-z]): At least one lowercase letter
(?=.*?[0-9]): At least one digit
(?=.*?[#?!@$%^&*-]): At least one special character
.{8,}: Minimum 8 characters long

If the password matches the pattern, the function returns True , indicating a valid password. Otherwise, it returns False.

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Method 2: Custom Validation Function

Another approach is to write a custom function that checks each condition separately:

def validate_password(password):
    if len(password) < 8:
        return False
    if not any(char.isupper() for char in password):
        return False
    if not any(char.islower() for char in password):
        return False
    if not any(char.isdigit() for char in password):
        return False
    special_chars = "#?!@$%^&*-"
    if not any(char in special_chars for char in password):
        return False
    return True
print(validate_password("P@ssword"))

Output:

False

I have executed the above example code and added the screenshot below.

This function checks if the password meets the following criteria:

Minimum length of 8 characters
Contains at least one uppercase letter
Contains at least one lowercase letter
Contains at least one digit
Contains at least one special character from the set "#?!@$%^&*-"

If the password fails any of these checks, the function returns False. If it passes all checks, it returns True.

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Method 3: Use the passlib Library

Python’s passlib library provides a convenient way to handle password hashing and validation. Here’s an example:

from passlib.hash import pbkdf2_sha256

def validate_password(password):
    return pbkdf2_sha256.verify(password, pbkdf2_sha256.hash(password))

This code uses the pbkdf2_sha256 algorithm from passlib to hash the password and then verify if the password matches its hashed value. If the verification succeeds, the function returns True , indicating a valid password.

Read How to Use Built-In Functions in Python?

Examples

Here are some examples of using the password validation functions:

password1 = "Str0ngP@ssw0rd"
password2 = "weakpass"

print(validate_password(password1))
print(validate_password(password2))

Output:

True
False

In this example, password1 meets all the criteria for a strong password, so it returns True, while password2 is considered weak and returns False.

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Conclusion

In this tutorial, I discussed how to validate passwords in Python, We discussed various methods to validate passwords in Python like using regular expressions, custom validation functions, or libraries like passlib with examples.