How to interrupt stdin.read(1) manually in Python?

Question

import sys
import threading
import tty
import termios


def loop():
    fd = sys.stdin.fileno()
    mode = termios.tcgetattr(fd)
    tty.setraw(fd)
    try:
        while True:
            sys.stdin.read(1)
    finally:
        termios.tcsetattr(fd, termios.TCSADRAIN, mode)


threading.Thread(target=loop).start()

I tried to manually send End-Of-Transmission character using sys.stdin.write(chr(4)) but it results in io.UnsupportedOperation: not writable.

I tried to close stdin but it will not terminate blocking read(1) method immediately. It triggers an exception after I typed another key.

I tried seletors but selector.select() need extra keys after I invoked selector.close(). And selector it self needs an event loop and this loop becomes uninterruptable.

bitdancer · Answer 1 · 2019-12-25T13:14:44.040

If you run the loop in a thread then it will be hard to interrupt and also keep original process running. But it's easy to run this loop in a subprocess. So you can interrupt the subprocess to interrupt the blocking stdin.read(1)

import os
import sys
import tty
import termios
import time
import signal
from multiprocessing import Process

def loop():
    # https://stackoverflow.com/questions/30134297/python-multiprocessing-stdin-input
    # Subprocess stdin will be set to os.devnull. So we need to reopen it here.
    # Use parent process stdin(fd=0) instead of subprocess stdin(fd=7)
    sys.stdin = open(0)  #
    fd = sys.stdin.fileno()
    mode = termios.tcgetattr(fd)
    tty.setraw(fd)
    try:
        while True:
            ch = sys.stdin.read(1)
            if ord(ch) == 3:
                break
    except KeyboardInterrupt:
        print("interrupted!\r\n", end="")
    finally:
        termios.tcsetattr(fd, termios.TCSADRAIN, mode)


if __name__ == '__main__':
    p = Process(target=loop)
    p.start()
    time.sleep(1)
    os.kill(p.pid, signal.SIGINT)
    p.join()
    print("done")

How to interrupt stdin.read(1) manually in Python?

1 Answers1