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

Loops are fundamental structures in Python programming for executing a block of code repeatedly until a certain condition is met. However, there are scenarios where you might want to terminate a while loop prematurely, especially when you want to give the user the ability to interrupt the loop with a keystroke. In this article, we’ll explore some simple methods to achieve this using Python.

Kill a While Loop with a Keystroke in Python

Below are some of the methods to kill a While Loop with a keystroke in Python:

• Using KeyboardInterrupt
• Using keyboard Library
• Utilizing msvcrt Module

Kill a While Loop with a Keystroke Using KeyboardInterrupt

In this example, below code a variable num with 11 and enters an infinite loop, printing and incrementing num by 2 in each iteration until an even number is encountered. The loop is slowed down by one second. If interrupted by a keyboard interrupt (Ctrl+C), it passes and continues with the program, printing “Continuing with the program.”.

Python3

import time

try:
    num = 11
    while True:
        if num % 2 == 0:
            break
        print(num)
        num = num + 2
        time.sleep(1)  # Using to slow the while loop by one second 🙂
except KeyboardInterrupt:
    pass

print("Continuing with the program")

Output:

11
13
15
17
Continuing with the program

Kill a While Loop with a Keystroke Using keyboard Library

The keyboard library provides a straightforward way to capture keyboard events, making it an excellent choice for handling keystrokes within your Python programs. First, install the library using the following command:

pip install keyboard

In this example, below code uses the keyboard library to create an infinite loop (main_loop) where “Working…” is printed continuously. It checks for the ‘q’ key press using keyboard.is_pressed('q'), and if detected, it prints “Loop terminated by user” and breaks out of the loop.

Python3

import keyboard

def main_loop():
    while True:
        # Your loop logic here
        print("Working...")

        # Check for 'q' key press to break the loop
        if keyboard.is_pressed('q'):
            print("Loop terminated by user.")
            break

if __name__ == "__main__":
    main_loop()

Output:

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

Kill a While Loop with a Keystroke Utilizing msvcrt Module

The msvcrt module, specific to Windows systems, allows capturing keystrokes without the need for external libraries. Here’s an example of using it to terminate a while loop: This method works on Windows and is more suitable for scenarios where external libraries are not preferred.

Python3

import msvcrt

def main_loop():
    while True:
        # Your loop logic here
        print("Working...")

        # Check for a key press to break the loop
        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...
Working...
Working...
Working...
Loop terminated by user.