How to Kill a While Loop with a Keystroke in Python?

While loops are used to repeatedly execute a block of code until a condition is met. But what if you want the user to stop the loop manually, say by pressing a key? Then you can do so by pressing a key. This article covers three simple ways to break a while loop using a keystroke:

• Using KeyboardInterrupt
• Using keyboard Library
• Utilizing msvcrt Module

Let's discuss them one by one:

Method 1: Using KeyboardInterrupt (Ctrl+C)

This method allows you to manually stop the loop by pressing Ctrl+C.

import time

try:
    num = 11
    while True: 
        if num % 2 == 0:
            break
        print(num)
        num = num + 2
        time.sleep(1)  # Wait 1 second before next iteration
except KeyboardInterrupt:
    pass

print("Continuing with the program")

Output:

11
13
15
17
Continuing with the program

Explanation:

• try...except KeyboardInterrupt catches manual interruption (Ctrl+C).
• loop prints odd numbers and stops once an even number is found or interrupted.

Method 2: Using the keyboard Library

This approach allows the user to press a specific key (like q) to exit the loop. But to implement this in our code we need to first install the keyboard library using this command:

pip install keyboard

Example:

import keyboard

def main_loop():
    while True:
        print("Working...")
        
        # Press 'q' to exit
        if keyboard.is_pressed('q'):
            print("Loop terminated by user.")
            break

if __name__ == "__main__":
    main_loop()

Output:

Working...
Working...
Working...
Working...
Loop terminated by user.

Method 3: Using msvcrt Module (Windows Only)

For Windows users, this method captures key presses without extra libraries.

import msvcrt

def main_loop():
    while True:
        print("Working...")
        
        # Check if any key is pressed
        if msvcrt.kbhit():
            key = msvcrt.getch().decode()
            if key == 'q':
                print("Loop terminated by user.")
                break

if __name__ == "__main__":
    main_loop()

Output:

Working...
Working...
Working...
Working...
Loop terminated by user.

Explanation:

• msvcrt.kbhit() checks for any key press.
• msvcrt.getch() captures the pressed key (e.g., 'q') to break the loop.

Also read: KeyboardInterrupt, keyboard library.

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Article Tags :

• Python
• Python Programs
• python-basics
• Python-exceptions

Practice Tags :

• python