35.8. "pty" — Pseudo-terminal utilities
***************************************

**Source code:** Lib/pty.py

======================================================================

The "pty" module defines operations for handling the pseudo-terminal
concept: starting another process and being able to write to and read
from its controlling terminal programmatically.

Because pseudo-terminal handling is highly platform dependent, there
is code to do it only for Linux. (The Linux code is supposed to work
on other platforms, but hasn’t been tested yet.)

The "pty" module defines the following functions:

pty.fork()

   Fork. Connect the child’s controlling terminal to a pseudo-
   terminal. Return value is "(pid, fd)". Note that the child  gets
   *pid* 0, and the *fd* is *invalid*. The parent’s return value is
   the *pid* of the child, and *fd* is a file descriptor connected to
   the child’s controlling terminal (and also to the child’s standard
   input and output).

pty.openpty()

   Open a new pseudo-terminal pair, using "os.openpty()" if possible,
   or emulation code for generic Unix systems. Return a pair of file
   descriptors "(master, slave)", for the master and the slave end,
   respectively.

pty.spawn(argv[, master_read[, stdin_read]])

   Spawn a process, and connect its controlling terminal with the
   current process’s standard io. This is often used to baffle
   programs which insist on reading from the controlling terminal.

   The functions *master_read* and *stdin_read* should be functions
   which read from a file descriptor. The defaults try to read 1024
   bytes each time they are called.

   Changed in version 3.4: "spawn()" now returns the status value from
   "os.waitpid()" on the child process.


35.8.1. Example
===============

The following program acts like the Unix command *script(1)*, using a
pseudo-terminal to record all input and output of a terminal session
in a “typescript”.

   import argparse
   import os
   import pty
   import sys
   import time

   parser = argparse.ArgumentParser()
   parser.add_argument('-a', dest='append', action='store_true')
   parser.add_argument('-p', dest='use_python', action='store_true')
   parser.add_argument('filename', nargs='?', default='typescript')
   options = parser.parse_args()

   shell = sys.executable if options.use_python else os.environ.get('SHELL', 'sh')
   filename = options.filename
   mode = 'ab' if options.append else 'wb'

   with open(filename, mode) as script:
       def read(fd):
           data = os.read(fd, 1024)
           script.write(data)
           return data

       print('Script started, file is', filename)
       script.write(('Script started on %s\n' % time.asctime()).encode())

       pty.spawn(shell, read)

       script.write(('Script done on %s\n' % time.asctime()).encode())
       print('Script done, file is', filename)
