How to interrupt a loop in python with the input of a key but without stopping the cycle to verify i-CodePudding


while(True):

   print("Enter to the bucle")
   with open('the_file.txt', 'w') as f:
       f.write('Hello world!\n')
   f.close()

   #if at some point during the execution of this loop press the letter, for example the key q, that a break is set and the while () loop closes

The problem i found is that if i use an input () and save the key as a string, that would be stopping the loop at the keyboard input wait point, but what i was looking for is that it doesn't have a point where it stops for wait for the keyboard input but simply if at some point the q was pressed, the cycle would end and it would not be executed again

CodePudding user response：

Sample code using threading. We run task in the background and parse user input for key/enter in another thread.

is_interrupt_task = True will interrupt the task otherwise it will not even if main thread has already exited.

Code

import logging
import threading
import time

format = '%(asctime)s: %(message)s'
logging.basicConfig(format=format, level=logging.INFO, datefmt='%H:%M:%S')


def task(name):
    logging.info(f'Thread {name}: starting')
    for i in range(10):
        time.sleep(i)
        logging.info(f'Thread {name}: sleeps for {i}s')

    logging.info(f'Thread {name}: task is completed.')


if __name__ == "__main__":
    # Run task in the background.
    is_interrupt_task = True
    mytask = threading.Thread(target=task, args=(1,), daemon=is_interrupt_task)
    mytask.start()

    logging.info('starting main loop ...')
    while True:  
        userinput = input()
        command = userinput.strip()

        if command:  # almost all keys
            logging.info("main quits")
            break

        # if command == 'q':
            # logging.info("main quits")
            # break

Example task is interrupted

16:12:29: Thread 1: starting
16:12:29: starting main loop ...
16:12:29: Thread 1: sleeps for 0s
16:12:30: Thread 1: sleeps for 1s
16:12:32: Thread 1: sleeps for 2s
16:12:35: Thread 1: sleeps for 3s
q
16:12:36: main quits

Example task is allowed to finish

is_interrupt_task = False

16:11:12: Thread 1: starting
16:11:12: starting main loop ... 
16:11:12: Thread 1: sleeps for 0s
16:11:13: Thread 1: sleeps for 1s
16:11:15: Thread 1: sleeps for 2s
16:11:18: Thread 1: sleeps for 3s
q
16:11:22: main quits
16:11:22: Thread 1: sleeps for 4s
16:11:27: Thread 1: sleeps for 5s
16:11:33: Thread 1: sleeps for 6s
16:11:40: Thread 1: sleeps for 7s
16:11:48: Thread 1: sleeps for 8s
16:11:57: Thread 1: sleeps for 9s
16:11:57: Thread 1: task is completed.