How to get tcsh arrow keys when connected through python2.7 subprocess.PIPE

Question

I am writing a simple remote shell program in python2.7. It runs the shell like this:

p = subprocess.Popen(['/usr/bin/tcsh', '-i'],
                     stdin  = subprocess.PIPE,
                     stdout = subprocess.PIPE,
                     stderr = subprocess.PIPE)

This lets me run commands but the arrow keys aren't working:

Warning: no access to tty (Bad file descriptor).
Thus no job control in this shell.
% date
Sun Dec 25 10:54:47 PST 2022
% 
^[[A: Command not found.
% 

I tried the same thing with bash and the arrow keys are working. How should I modify the python2.7 code above to get working arrow keys in tcsh ?

Answer 1

Use a TTY instead of pipes for stdin, stdout, and stderr. Something like this:

import pty
import subprocess

master, slave = pty.openpty()

p = subprocess.Popen(['/usr/bin/tcsh', '-i'],
                     stdin  = slave,
                     stdout = slave,
                     stderr = slave)

And then later in your code where you're reading and writing to the pipes, change it to read and write to master instead.