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+\section{Built-in Module \sectcode{signal}}
+
+\bimodindex{signal}
+This module provides mechanisms to write signal handlers in Python.
+
+{\bf Warning:} Some care must be taken if both signals and threads
+will be used in the same program. The fundamental thing to remember
+in using signals and threads simultaneously is: always perform
+\code{signal()} operations in the main thread of execution. Any
+thread can perform a \code{alarm()}, \code{getsignal()}, or
+\code{pause()}; only the main thread can set a new signal handler, and
+the main thread will be the only one to receive signals. This means
+that signals can't be used as a means of interthread communication.
+Use locks instead.
+
+The variables defined in the signal module are:
+
+\renewcommand{\indexsubitem}{(in module signal)}
+\begin{datadesc}{SIG_DFL}
+ This is one of two standard signal handling options; it will simply
+ perform the default function for the signal. For example, on most
+ systems the default action for SIGQUIT is to dump core and exit,
+ while the default action for SIGCLD is to simply ignore it.
+\end{datadesc}
+
+\begin{datadesc}{SIG_IGN}
+ This is another standard signal handler, which will simply ignore
+ the given signal.
+\end{datadesc}
+
+\begin{datadesc}{SIG*}
+ All the signal numbers are defined symbolically. For example, the
+ hangup signal is defined as \code{signal.SIGHUP}; the variable names
+ are identical to the names used in C programs, as found in
+ \file{signal.h}.
+ The UNIX man page for \file{signal} lists the existing signals (on
+ some systems this is \file{signal(2)}, on others the list is in
+ \file{signal(7)}).
+ Note that not all systems define the same set of signal names; only
+ those names defined by the system are defined by this module.
+\end{datadesc}
+
+The signal module defines the following functions:
+
+\begin{funcdesc}{alarm}{time}
+ If \var{time} is non-zero, this function requests that a
+ \code{SIGALRM} signal be sent to the process in \var{time} seconds.
+ Any previously scheduled alarm is canceled (i.e. only one alarm can
+ be scheduled at any time). The returned value is then the number of
+ seconds before any previously set alarm was to have been delivered.
+ If \var{time} is zero, no alarm id scheduled, and any scheduled
+ alarm is canceled. The return value is the number of seconds
+ remaining before a previously scheduled alarm. If the return value
+ is zero, no alarm is currently scheduled. (See the UNIX man page
+ \code{alarm(2)}.)
+\end{funcdesc}
+
+\begin{funcdesc}{getsignal}{signalnum}
+ Returns the current signal handler for the signal \var{signalnum}.
+ The returned value may be a callable Python object, or one of the
+ special values \code{signal.SIG_IGN} or \code{signal.SIG_DFL}.
+\end{funcdesc}
+
+\begin{funcdesc}{pause}{}
+ Causes the process to sleep until a signal is received; the
+ appropriate handler will then be called. Returns nothing. (See the
+ UNIX man page \code{signal(2)}.)
+\end{funcdesc}
+
+\begin{funcdesc}{signal}{signalnum\, handler}
+ Sets the handler for signal \var{signalnum} to the function
+ \var{handler}. \var{handler} can be any callable Python object, or
+ one of the special values \code{signal.SIG_IGN} or
+ \code{signal.SIG_DFL}. The previous signal handler will be
+ returned. (See the UNIX man page \code{signal(2)}.)
+
+ If threads are enabled, this function can only be called from the
+ main thread; attempting to call it from other threads will cause a
+ \code{ValueError} exception will be raised.
+\end{funcdesc}