[Practice Problems] Python While Loops - Visually Explained

Added: 2026-05-21

[00:00:00]Did you get a chance to work through our Y loops practice exercises? If not, no worries. You can find the notebook linked in the description. In this video, we'll walk through the solutions step by step. All right, let's jump into problem one. In the first problem, we have three scenarios.

[00:00:16]For each scenario, we need to decide whether a for loop or a while loop is a better fit and then explain why. The first scenario describes asking a user for their phone number until they enter it in the correct format. Since we don't know how many attempts it'll take for the user to input a valid phone number, we should use a while loop. In the second scenario, the task is to print each name in a class roster list. In this case, we have all the names in a list before we need to print them. So, it's best to use a for loop. The third scenario describes attempting to connect to the internet. Like the first scenario, we don't know ahead of time how many attempts will be required. So, a while loop would be the best fit here.

[00:00:58]When we compare these answers, we can see a clear rule of thumb. If the number of iterations is known ahead of time, the for loop is usually a better fit.

[00:01:08]But if the number of iterations is unknown or variable, a while loop is usually the better fit. Great. That gives us a quick decision framework we can reuse in real projects. All right, let's move on to problem two. In this problem, we're writing a simple login check.

[00:01:24]We need to keep asking for password until the user types the correct value which is sunset 42. To start, we create the correct password variable and the user input variable. We set this variable equal to a placeholder so our loop has something to compare to before the first prompt. After creating those variables, we write a while loop that runs as long as user input is not equal to the correct password.

[00:01:55]Inside the loop, we prompt the user to enter a password.

[00:01:59]After the user enters a value, we check whether the password is still incorrect.

[00:02:04]If it is still incorrect, we print incorrect password. Try again.

[00:02:09]But if the user enters sunset 42, the loop condition fails on the next check and the loop ends. After the loop, we print access granted.

[00:02:22]When we run this code, wrong passwords keep the loop going. But when the correct password is entered, the loop exits and access is granted. Awesome.

[00:02:32]Asking for user input is one of the most common real world uses for while loops.

[00:02:36]In problem three, we'll refactor our solution from problem two to use the while true syntax and break keyword.

[00:02:44]We'll start with our code from problem two.

[00:02:48]Instead of defining a placeholder variable and writing the stopping condition in the while header, we simply write while true. Next, to avoid creating an infinite loop, we need to add an exit condition. To do this, we can simply add an else to our conditional.

[00:03:04]The code inside this else block will only be run if the user inputs the correct password.

[00:03:10]In this case, we print access granted and break out of the while loop. When the break keyword is run, the loop exits immediately.

[00:03:19]To confirm this, let's change the final print statement to say end of program.

[00:03:23]When we run this version of the code, the behavior is the same from the user's perspective. Wrong attempts keep repeating and the correct password ends the loop right away.

[00:03:34]Great. Now you're familiar with both common styles for while loops and understand when it's best to use a while loop instead of a for loop. If you're looking to learn more Python, check out our video on error handling. It's really useful when working with user input in Python. We're working on lots more Python explainer videos like this one, so be sure to subscribe so you don't miss out. If you have any questions or topics that you'd like to learn about, let us know in the comments below. We'd love to hear from you. Thanks for watching.