While Loops

Unlike for loops, while loops are non-deterministic – the program (and programmer!) doesn't always know how many times the loop will repeat before it finally calls it quits. Instead, it depends on a particular condition – usually waiting for a boolean to flip from True to False. 🕵️‍♂️

Danger

If the condition never becomes False, an infinite loop can be created. If you encounter an infinite loop, usually Ctrl+C will kill the program (for basic scripting). (Don't worry, it happens to everyone! Even the pros forget to escape sometimes. 🏃‍♂️💨)

The basic form of a while loop is:

while expr:
    <code block>

The expression is evaluated at the start of each loop, and if it is True, the loop will run. It's like a party that keeps going as long as the music is playing! 🎶

For example:

keep_looping = True
while keep_looping:
    user_input = input("Enter 'exit' to stop the loop: ")
    if user_input.lower() == 'exit':
        print("Exiting the loop. Goodbye! 👋")
        keep_looping = False
    else:
        print(f"You entered: {user_input} 🤖")

Until the user enters "exit", this loop will keep echoing the user input infinitely. Careful not to get stuck in an infinite loop.

Tip

It is possible that a while loop will never run if, when it is reached, the condition it checks is already False. 🚫

Another common pattern is to check equality and increment/decrement the value on each iteration:

value = 10

while value > 0:
    print(f"Current value: {value}")
    value -= 1  # Decrease the value by 1 each iteration
print("Loop has ended. All done! 🏁")

Challenge

Try writing your own while loop that is different from the examples above! Bonus points for creativity – maybe count sheep, print emojis, or make a countdown to pizza time! 🍕⏳