:mod:`termios` --- POSIX style tty control

.. module:: termios
 :platform: Unix
 :synopsis: POSIX style tty control.

.. index::
 pair: POSIX; I/O control
 pair: tty; I/O control

This module provides an interface to the POSIX calls for tty I/O control. For a complete description of these calls, see :manpage:`termios(3)` Unix manual page. It is only available for those Unix versions that support POSIX termios style tty I/O control configured during installation.

All functions in this module take a file descriptor fd as their first argument. This can be an integer file descriptor, such as returned by sys.stdin.fileno(), or a :term:`file object`, such as sys.stdin itself.

This module also defines all the constants needed to work with the functions provided here; these have the same name as their counterparts in C. Please refer to your system documentation for more information on using these terminal control interfaces.

The module defines the following functions:

.. function:: tcgetattr(fd)

 Return a list containing the tty attributes for file descriptor *fd*, as
 follows: ``[iflag, oflag, cflag, lflag, ispeed, ospeed, cc]`` where *cc* is a
 list of the tty special characters (each a string of length 1, except the
 items with indices :const:`VMIN` and :const:`VTIME`, which are integers when
 these fields are defined). The interpretation of the flags and the speeds as
 well as the indexing in the *cc* array must be done using the symbolic
 constants defined in the :mod:`termios` module.

.. function:: tcsetattr(fd, when, attributes)

 Set the tty attributes for file descriptor *fd* from the *attributes*, which is
 a list like the one returned by :func:`tcgetattr`. The *when* argument
 determines when the attributes are changed: :const:`TCSANOW` to change
 immediately, :const:`TCSADRAIN` to change after transmitting all queued output,
 or :const:`TCSAFLUSH` to change after transmitting all queued output and
 discarding all queued input.

.. function:: tcsendbreak(fd, duration)

 Send a break on file descriptor *fd*. A zero *duration* sends a break for
 0.25--0.5 seconds; a nonzero *duration* has a system dependent meaning.

.. function:: tcdrain(fd)

 Wait until all output written to file descriptor *fd* has been transmitted.

.. function:: tcflush(fd, queue)

 Discard queued data on file descriptor *fd*. The *queue* selector specifies
 which queue: :const:`TCIFLUSH` for the input queue, :const:`TCOFLUSH` for the
 output queue, or :const:`TCIOFLUSH` for both queues.

.. function:: tcflow(fd, action)

 Suspend or resume input or output on file descriptor *fd*. The *action*
 argument can be :const:`TCOOFF` to suspend output, :const:`TCOON` to restart
 output, :const:`TCIOFF` to suspend input, or :const:`TCION` to restart input.

.. seealso::

 Module :mod:`tty`
 Convenience functions for common terminal control operations.

Example

Here's a function that prompts for a password with echoing turned off. Note the technique using a separate :func:`tcgetattr` call and a :keyword:`try` ... :keyword:`finally` statement to ensure that the old tty attributes are restored exactly no matter what happens:

def getpass(prompt="Password: "):
 import termios, sys
 fd = sys.stdin.fileno()
 old = termios.tcgetattr(fd)
 new = termios.tcgetattr(fd)
 new[3] = new[3] & ~termios.ECHO # lflags
 try:
 termios.tcsetattr(fd, termios.TCSADRAIN, new)
 passwd = input(prompt)
 finally:
 termios.tcsetattr(fd, termios.TCSADRAIN, old)
 return passwd

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