# 8.11 `pty` -- Pseudo-terminal utilities

Availability: IRIX, Linux.

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 dependant, there is code to do it only for SGI and Linux. (The Linux code is supposed to work on other platforms, but hasn't been tested yet.)

The `pty` module defines the following functions:

`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).

`openpty`( | )

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

`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.