Open New Pseudo Terminal Pair Using Python

Pseudo-terminals (pty) are an advanced and powerful technique in Python when we are dealing with terminal-based processes or simulating interactive sessions programmatically.

A pseudo-terminal allows a process to connect to a real terminal. Python provides a built-in pty module that helps in creating and managing these terminal pairs. In this article, we will learn how to open a new pseudo-terminal pair using Python.

Using pty.openpty()

The pty module in Python provides the openpty() function that returns a tuple containing file descriptors for the master and slave ends of a new pseudo-terminal pair.

Example

Following is an example, which shows how to create a new pty pair using pty.openpty() -

import os
import pty

# Open a new pseudo-terminal pair
master_fd, slave_fd = pty.openpty()

# Get the name of the slave device
slave_name = os.ttyname(slave_fd)

print("Master FD:", master_fd)
print("Slave FD:", slave_fd)
print("Slave device path:", slave_name)

Following is the output of the above program -

Master FD: 3
Slave FD: 4
Slave device path: /dev/pts/3

Using pty to Spawn a Shell

The other method available in Python is Spawn a shell that is connected to the slave end of the pseudo-terminal. This is useful for terminal emulation or sandboxing shell processes.

Example

Following is an example that shows how to spawn a shell and interact with it through the master end of the pty -

import os
import pty
import subprocess

master_fd, slave_fd = pty.openpty()

# Start a shell connected to the slave
proc = subprocess.Popen(
    ['/bin/bash'],
    stdin=slave_fd,
    stdout=slave_fd,
    stderr=slave_fd,
    close_fds=True
)

# Interact with the shell through the master
os.write(master_fd, b'echo Hello from pty\n')
output = os.read(master_fd, 1024)

print("Shell Output:", output.decode())

When we run the above program, a new bash shell is started, and it prints the message from our Python script -

Shell Output: Hello from pty

Finally, we can conclude, opening a pty pair in Python is straightforward and useful for many advanced usecases -

• We can use pty.openpty() to create a low-level terminal emulation channel.
• We can use os.ttyname() to identify the slave terminal path.
• We can connect subprocesses, such as shells, to the slave end to simulate terminal sessions.

Note: The pty module is available only on Unix-like systems and is not supported on Windows. When we want to use the pseudo-terminal pair in Windows, we can use the pywinpty on Windows 10+.