Built-in Module signal

signal This module provides mechanisms to use signal handlers in Python. Some general rules for working with signals handlers:

A handler for a particular signal, once set, remains installed until it is explicitly reset (i.e. Python uses the BSD style interface).
There is no way to ``block'' signals temporarily from critical sections (since this is not supported by all flavors).
Although Python signal handlers are called asynchronously as far as the Python user is concerned, they can only occur between the ``atomic'' instructions of the Python interpreter. This means that signals arriving during long calculations implemented purely in C (e.g. regular expression matches on large bodies of text) may be delayed for an arbitrary amount of time.
When a signal arrives during an I/O operation, it is possible that the I/O operation raises an exception after the signal handler returns. This is dependent on the underlying system's semantics regarding interrupted system calls.
Because the C signal handler always returns, it makes little sense to catch synchronous errors like SIGFPE or SIGSEGV.
Python installs a small number of signal handlers by default: SIGPIPE is ignored (so write errors on pipes and sockets can be reported as ordinary Python exceptions), SIGINT is translated into a KeyboardInterrupt exception, and SIGTERM is caught so that necessary cleanup (especially sys.exitfunc) can be performed before actually terminating. All of these can be overridden.
Some care must be taken if both signals and threads are used in the same program. The fundamental thing to remember in using signals and threads simultaneously is: always perform signal() operations in the main thread of execution. Any thread can perform an alarm(), getsignal(), or pause(); only the main thread can set a new signal handler, and the main thread will be the only one to receive signals (this is enforced by the Python signal module, even if the underlying thread implementation supports sending signals to individual threads). 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:
$\begin{datadesc}{SIG_DFL} This is one of two standard signal handling options; ... ...xit, while the default action for SIGCLD is to simply ignore it. \end{datadesc}$

$\begin{datadesc}{SIG_IGN} This is another standard signal handler, which will simply ignore the given signal. \end{datadesc}$

$\begin{datadesc}{SIG*} All the signal numbers are defined symbolically. For exa... ...ly those names defined by the system are defined by this module. \end{datadesc}$

$\begin{datadesc}{NSIG} One more than the number of the highest signal number. \end{datadesc}$
The signal module defines the following functions:
$\begin{funcdesc}{alarm}{time} If \var{time} is non-zero, this function requests... ...currently scheduled. (See the \UNIX{} man page \code{alarm(2)}.) \end{funcdesc}$

$\begin{funcdesc}{getsignal}{signalnum} Return the current signal handler for th... ... that the previous signal handler was not installed from Python. \end{funcdesc}$

$\begin{funcdesc}{pause}{} Cause the process to sleep until a signal is received... ...d. Returns nothing. (See the \UNIX{} man page \code{signal(2)}.) \end{funcdesc}$

$\begin{funcdesc}{signal}{signalnum\, handler} Set the handler for signal \var{s... ...rence manual for a description of frame objects). \obindex{frame} \end{funcdesc}$