cpython/Doc/lib/libtermios.tex

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\section{\module{termios} ---
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\POSIX{} style tty control}
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\declaremodule{builtin}{termios}
\platform{Unix}
\modulesynopsis{\POSIX\ style tty control.}
\indexii{\POSIX}{I/O control}
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\indexii{tty}{I/O control}
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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
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\UNIX{} manual pages. It is only available for those \UNIX{} versions
that support \POSIX{} \emph{termios} style tty I/O control (and then
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only if configured at installation time).
All functions in this module take a file descriptor \var{fd} as their
first argument. This can be an integer file descriptor, such as
returned by \code{sys.stdin.fileno()}, or a file object, such as
\code{sys.stdin} itself.
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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.
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The module defines the following functions:
\begin{funcdesc}{tcgetattr}{fd}
Return a list containing the tty attributes for file descriptor
\var{fd}, as follows: \code{[}\var{iflag}, \var{oflag}, \var{cflag},
\var{lflag}, \var{ispeed}, \var{ospeed}, \var{cc}\code{]} where
\var{cc} is a list of the tty special characters (each a string of
length 1, except the items with indices \constant{VMIN} and
\constant{VTIME}, which are integers when these fields are
defined). The interpretation of the flags and the speeds as well as
the indexing in the \var{cc} array must be done using the symbolic
constants defined in the \module{termios}
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module.
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\end{funcdesc}
\begin{funcdesc}{tcsetattr}{fd, when, attributes}
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Set the tty attributes for file descriptor \var{fd} from the
\var{attributes}, which is a list like the one returned by
\function{tcgetattr()}. The \var{when} argument determines when the
attributes are changed: \constant{TCSANOW} to change immediately,
\constant{TCSADRAIN} to change after transmitting all queued output,
or \constant{TCSAFLUSH} to change after transmitting all queued
output and discarding all queued input.
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\end{funcdesc}
\begin{funcdesc}{tcsendbreak}{fd, duration}
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Send a break on file descriptor \var{fd}. A zero \var{duration} sends
a break for 0.25--0.5 seconds; a nonzero \var{duration} has a system
dependent meaning.
\end{funcdesc}
\begin{funcdesc}{tcdrain}{fd}
Wait until all output written to file descriptor \var{fd} has been
transmitted.
\end{funcdesc}
\begin{funcdesc}{tcflush}{fd, queue}
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Discard queued data on file descriptor \var{fd}. The \var{queue}
selector specifies which queue: \constant{TCIFLUSH} for the input
queue, \constant{TCOFLUSH} for the output queue, or
\constant{TCIOFLUSH} for both queues.
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\end{funcdesc}
\begin{funcdesc}{tcflow}{fd, action}
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Suspend or resume input or output on file descriptor \var{fd}. The
\var{action} argument can be \constant{TCOOFF} to suspend output,
\constant{TCOON} to restart output, \constant{TCIOFF} to suspend
input, or \constant{TCION} to restart input.
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\end{funcdesc}
\begin{seealso}
\seemodule{tty}{Convenience functions for common terminal control
operations.}
\end{seealso}
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\subsection{Example}
\nodename{termios Example}
Here's a function that prompts for a password with echoing turned
off. Note the technique using a separate \function{tcgetattr()} call
and a \keyword{try} ... \keyword{finally} statement to ensure that the
old tty attributes are restored exactly no matter what happens:
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\begin{verbatim}
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def getpass(prompt = "Password: "):
import termios, sys
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fd = sys.stdin.fileno()
old = termios.tcgetattr(fd)
new = termios.tcgetattr(fd)
new[3] = new[3] & ~termios.ECHO # lflags
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try:
termios.tcsetattr(fd, termios.TCSADRAIN, new)
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passwd = raw_input(prompt)
finally:
termios.tcsetattr(fd, termios.TCSADRAIN, old)
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return passwd
\end{verbatim}