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# 35.7. `termios` — POSIX style tty control

Platforms: Unix

This module provides an interface to the POSIX calls for tty I/O control. For a complete description of these calls, see the POSIX or Unix manual pages. It is only available for those Unix versions that support POSIX termios style tty I/O control (and then only if configured at installation time).

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 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:

`termios.``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 `VMIN` and `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 `termios` module.

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

`termios.``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.

`termios.``tcdrain`(fd)
  Wait until all output written to file descriptor fd has been transmitted.

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

`termios.``tcflow`(fd, action)
  Suspend or resume input or output on file descriptor fd. The action argument can be `TCOOFF` to suspend output, `TCOON` to restart output, `TCIOFF` to suspend input, or `TCION` to restart input.

See also

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

## 35.7.1. Example

Here’s a function that prompts for a password with echoing turned off. Note the technique using a separate `tcgetattr()` call and a `try` ... `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 = raw_input(prompt)
        finally:
            termios.tcsetattr(fd, termios.TCSADRAIN, old)
        return passwd

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