Open a Linux pty for another process to attach to

idleterm.py

#!/usr/bin/python3
#
# idleterm.py: Open a pty so that a process from elsewhere - such as a gdb
#              inferior - can attach to it and copy the IO between the pty and
#              this process's stdin and stdout.
#
#              This is a Python version of the idleterm program at
#              https://stackoverflow.com/a/71314902/2319122
#
# Ben Cohen, April 2022.
#
import pty
import os
import select
import sys
import termios
import threading

if (os.isatty(sys.stdin.fileno())):
    attrs = termios.tcgetattr(sys.stdin)
    attrs[3] = attrs[3] & ~(termios.ISIG | termios.ICANON | termios.ECHO)
    termios.tcsetattr(sys.stdin, termios.TCSANOW, attrs)

mfd, sfd = pty.openpty()
print(f"pid = {os.getpid()}   tty = {os.ttyname(sfd)}")

def do_copy(from_fd, to_fd):
    while True:
        rfds, wfds, xfds = select.select([from_fd], [], [])
        if from_fd in rfds:
            data = os.read(from_fd, 1)
            if len(data) > 0:
                os.write(to_fd, data)

t1 = threading.Thread(target=do_copy, args=(mfd, sys.stdout.fileno()))
t2 = threading.Thread(target=do_copy, args=(sys.stdin.fileno(), mfd))
t1.start()
t2.start()
t1.join()
t2.join()