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Lesson-16

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16-exercise-password-checker

Exercise: Password Checker

Description here...

Lesson-16

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python-course

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16-exercise-password-checker

Exercise: Password Checker

Description here...

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Lesson Objectives

- Practice Built-In Methods and Functions
- Practice Loops
- Practice Custom Functions

Lesson Summary

Build a Password Checker

In this lesson, we’re going to build a password checker logic with python.

We'll create logic similar to any sign-up page where it tells you that your password is weak... We all hate it, but it's a good excercise in Python.

So, Here’s the plan:

🙋‍♂️ Ask for username and password
✔️ At least 8+ characters
✔️ Check for lowercase letter
✔️ Check for uppercase letter
✔️ Check for digits
✔️ Check for symbols
✔️ Check for spaces
📜 Report if password is secure enough.

Same as previously - Pause here and try to do it on your own (without ChatGPT). Then come back and let's do it together.

Ready? Set. Code 🚀

🙋‍♂️ Ask User Input

The first step is simple: ask the user for their username and password.

#🙋‍♂️ User Input
print("Creating a new account")
username = input("Enter username: ")
password = input("Enter password: ")
print('-'*50)

Keep Going!
You're Doing Great✨

Keep Going!
You're Doing Great✨

🔒 Security Checks

Now, we need to make a series of checks.

For clarity, we'll create placeholders for each check to hold True/False values so we can print the results later on too.

check_length    = False
check_digit     = False
check_lower     = False
check_upper     = False
check_symbol    = False
check_no_spaces = False

Now our goal is to go one by one and set it to True if it passes the test. I'll combine it into a single snippet so it's easier to read:

# Security Checks
# ✔️ Length (minimum 8 characters)
if len(password) >= 8:
    check_length = True

#✔️ Contains no spaces
if ' ' not in password: 
    check_no_spaces = True

for char in password:
    #✔️ Contains at least one digit
    if char.isdigit():
        check_digit = True

    #✔️ Contains at least one uppercase letter
    elif char.isupper():
        check_upper = True

    #✔️ Contains at least one lowercase letter
    elif char.islower():
        check_lower = True

    #✔️ Contains at least one special character
    elif char in symbols:
        check_symbol = True

As you can see it's very simple to do checks, we just need to remember a few built-in methods or membership operators to create these tests.

Also notice that we're creating a loop for a string, because it's a sequence of characters, and we can look at each character until we satisfy a condition.

Step 3: Combining the Checks

Lastly, we need to create a logical statement if everything is good or notify the user what's wrong. That's why we created variables to hold True/False about each test earlier.

We could use AND operator to combine all tests:

#🔎 Check Results
if check_length and check_digit and check_lower and check_upper and check_symbol and check_no_spaces:
    print('✅ Account Created Successfully.')

else:
    print('❌ Password is not strong enough.')

But there are too many of them and it looks ugly.

So instead, we can combine them into a list and then use all() built-in function to check if all values are True. It will look much cleaner and easier to read.

#➕ Combine Checks 
checks = [check_length,
            check_digit,
            check_lower,
            check_upper ,
            check_symbol,
            check_no_spaces ]

#🔎 Check Results
if all(checks):
    print('✅ Account Created Successfully.')

else:
    print('❌ Password is not strong enough.')

💡 Try To Always Make Your Code More Readable!

Notify What's Wrong:

Lastly, If the password isn’t strong enough, the user should know why. Let's look at each check variable and display the message if it's False. And avoid elif in this case, because we want to make individual checks unrelated to each tother.

if all(checks):
    print('✅ Account Created Successfully.')

else:
    print('❌ Password is not strong enough.')

    if not check_length:
        print('❌ - At least 8 characters')

    if not check_symbol:
        print(f'❌ - At least one symbol ({symbols})')

    if not check_digit:
        print('❌ - At least one digit.')

    if not check_upper:
        print('❌ - At least one uppercase letter.')

    if not check_lower:
        print('❌ - At least one lowercase letter.')

    if not check_no_spaces:
        print('❌ - Should not contain spaces.')

Now the feedback is clear.

Wrapping It in a Function

Lastly, let's turn everything into a function and add doc-strings to describe our code:

def check_password(password):
    """Check the strength of your password.
    Checks:
    - Length (minimum 8 characters)
    - Contains at least one digit
    - Contains at least one uppercase letter
    - Contains at least one lowercase letter
    - Contains at least one special character
    - Contains no spaces

    Returns: True/False"""
    print('-'*50)
    print(f'Checking Password: {password}')

    #📦 Placeholders
    symbols      = '!@#$%^&*()_+-<>/{}|'
    check_length = False
    check_digit  = False
    check_lower  = False
    check_upper  = False
    check_symbol = False
    check_no_spaces = False

    # Security Checks
    # ✔️ Length (minimum 8 characters)
    if len(password) >= 8:
        check_length = True

    #✔️ Contains no spaces
    if ' ' not in password:
        check_no_spaces = True

    for char in password:
        #✔️ Contains at least one digit
        if char.isdigit():
            check_digit = True

        #✔️ Contains at least one uppercase letter
        elif char.isupper():
            check_upper = True

        #✔️ Contains at least one lowercase letter
        elif char.islower():
            check_lower = True

        #✔️ Contains at least one special character
        elif char in symbols:
            check_symbol = True

    # Display Results
    checks = [check_length,
                check_digit,
                check_lower,
                check_upper ,
                check_symbol,
                check_no_spaces ]

    if all(checks):
        print('✅ Account Created Successfully.')
        return True

    else:
        print('Password is not strong enough.')

        if not check_length:
            print('❌ - At least 8 characters')

        if not check_symbol:
            print(f'❌ - At least one symbol ({symbols})')

        if not check_digit:
            print('❌ - At least one digit.')

        if not check_upper:
            print('❌ - At least one uppercase letter.')

        if not check_lower:
            print('❌ - At least one lowercase letter.')

        if not check_no_spaces:
            print('❌ - Should not contain spaces.')

        return False

Also notice that I've added return statements if password is secure or not.

Test Multiple Password

Now that our code is wrapped into a function we can reuse it multiple times. So let's create a list of passwords to check, and then test them one by one by calling the function name.

#📦 Variables
#----------------------------------------------------------------------------------------------------
passwords = [
    "Abc%",
    "trongass9!",
    "P@2025",
    "Secure99X",
    "HelloWorld7&",
    "MyPwd2025$X",
    "Test$Pass9Z",
    "Abcde1#23XY",
    "UltraSafe",
    "Zz99!XyyzW"
]

# FUNCTION HERE:
# ...

#🎯 MAIN
#----------------------------------------------------------------------------------------------------
for password in passwords:
    check = check_password(password)
    print(f'Is Secure: {check}')

This will check each password one by one, giving clear feedback on how to make it more secure.

Final Thoughts

And that’s it! 🎉

Now you know how to create a Password Checker with Python.
No password can escape your security check now:

Safe, Safe, Safe, DETECTED...😂

Happy Coding!

🙋‍♂️ See you in the next lesson.
- EF

Homework

Follow along the lesson and create password checker.

✅ Then you can add another function to check usernames:
- At least 4 characters
- No Spaces
- Exclude Curse Words
- Add More Custom Rules ✨

⌨️ Happy Coding!

Questions

If you have any questions, leave them in the YouTube Comments.

Have a Question?

Keep Going!
You're Doing Great✨

Keep Going!
You're Doing Great✨

PS. Python can change your career and how you think about problems.
Be Careful 🙂

PS. Python can change your career and how you think about problems.
Be Careful 🙂