cpython/Doc/library/signal.rst

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:mod:`signal` --- Set handlers for asynchronous events
======================================================
.. module:: signal
:synopsis: Set handlers for asynchronous events.
This module provides mechanisms to use signal handlers in Python. Some general
rules for working with signals and their handlers:
* A handler for a particular signal, once set, remains installed until it is
explicitly reset (Python emulates the BSD style interface regardless of the
underlying implementation), with the exception of the handler for
:const:`SIGCHLD`, which follows the underlying implementation.
* There is no way to "block" signals temporarily from critical sections (since
this is not supported by all Unix 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 (such as 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 Unix system's semantics regarding interrupted system
calls.
* Because the C signal handler always returns, it makes little sense to catch
synchronous errors like :const:`SIGFPE` or :const:`SIGSEGV`.
* Python installs a small number of signal handlers by default: :const:`SIGPIPE`
is ignored (so write errors on pipes and sockets can be reported as ordinary
Python exceptions) and :const:`SIGINT` is translated into a
:exc:`KeyboardInterrupt` exception. 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 :func:`signal` operations in the main thread
of execution. Any thread can perform an :func:`alarm`, :func:`getsignal`,
:func:`pause`, :func:`setitimer` or :func:`getitimer`; 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 :mod:`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
inter-thread communication. Use locks instead.
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The variables defined in the :mod:`signal` module are:
.. data:: 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 :const:`SIGQUIT` is to dump core and exit, while the default action
for :const:`SIGCLD` is to simply ignore it.
.. data:: SIG_IGN
This is another standard signal handler, which will simply ignore the given
signal.
.. data:: SIG*
All the signal numbers are defined symbolically. For example, the hangup signal
is defined as :const:`signal.SIGHUP`; the variable names are identical to the
names used in C programs, as found in ``<signal.h>``. The Unix man page for
':cfunc:`signal`' lists the existing signals (on some systems this is
:manpage:`signal(2)`, on others the list is in :manpage:`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.
.. data:: NSIG
One more than the number of the highest signal number.
.. data:: ITIMER_REAL
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2008-04-05 01:47:45 -03:00
Decrements interval timer in real time, and delivers :const:`SIGALRM` upon expiration.
.. data:: ITIMER_VIRTUAL
Decrements interval timer only when the process is executing, and delivers
SIGVTALRM upon expiration.
.. data:: ITIMER_PROF
Decrements interval timer both when the process executes and when the
system is executing on behalf of the process. Coupled with ITIMER_VIRTUAL,
this timer is usually used to profile the time spent by the application
in user and kernel space. SIGPROF is delivered upon expiration.
The :mod:`signal` module defines one exception:
.. exception:: ItimerError
Raised to signal an error from the underlying :func:`setitimer` or
:func:`getitimer` implementation. Expect this error if an invalid
interval timer or a negative time is passed to :func:`setitimer`.
This error is a subtype of :exc:`IOError`.
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The :mod:`signal` module defines the following functions:
.. function:: alarm(time)
If *time* is non-zero, this function requests that a :const:`SIGALRM` signal be
sent to the process in *time* seconds. Any previously scheduled alarm is
canceled (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 *time* is zero, no alarm is scheduled, and any scheduled alarm is
canceled. If the return value is zero, no alarm is currently scheduled. (See
the Unix man page :manpage:`alarm(2)`.) Availability: Unix.
.. function:: getsignal(signalnum)
Return the current signal handler for the signal *signalnum*. The returned value
may be a callable Python object, or one of the special values
:const:`signal.SIG_IGN`, :const:`signal.SIG_DFL` or :const:`None`. Here,
:const:`signal.SIG_IGN` means that the signal was previously ignored,
:const:`signal.SIG_DFL` means that the default way of handling the signal was
previously in use, and ``None`` means that the previous signal handler was not
installed from Python.
.. function:: pause()
Cause the process to sleep until a signal is received; the appropriate handler
will then be called. Returns nothing. Not on Windows. (See the Unix man page
:manpage:`signal(2)`.)
.. function:: setitimer(which, seconds[, interval])
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2008-04-05 01:47:45 -03:00
Sets given interval timer (one of :const:`signal.ITIMER_REAL`,
:const:`signal.ITIMER_VIRTUAL` or :const:`signal.ITIMER_PROF`) specified
by *which* to fire after *seconds* (float is accepted, different from
:func:`alarm`) and after that every *interval* seconds. The interval
timer specified by *which* can be cleared by setting seconds to zero.
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2008-04-05 01:47:45 -03:00
When an interval timer fires, a signal is sent to the process.
The signal sent is dependent on the timer being used;
:const:`signal.ITIMER_REAL` will deliver :const:`SIGALRM`,
:const:`signal.ITIMER_VIRTUAL` sends :const:`SIGVTALRM`,
and :const:`signal.ITIMER_PROF` will deliver :const:`SIGPROF`.
The old values are returned as a tuple: (delay, interval).
Attempting to pass an invalid interval timer will cause a
:exc:`ItimerError`.
.. function:: getitimer(which)
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2008-04-05 01:47:45 -03:00
Returns current value of a given interval timer specified by *which*.
Merged revisions 59565-59594 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r59568 | facundo.batista | 2007-12-19 13:53:01 +0100 (Wed, 19 Dec 2007) | 3 lines Some minor cleanups. Thanks Mark Dickinson. ........ r59573 | raymond.hettinger | 2007-12-19 19:13:31 +0100 (Wed, 19 Dec 2007) | 1 line Fix issue 1661: Flags argument silently ignored in re functions with compiled regexes. ........ r59574 | guido.van.rossum | 2007-12-19 20:41:06 +0100 (Wed, 19 Dec 2007) | 7 lines Patch #1583 by Adam Olsen. This adds signal.set_wakeup_fd(fd) which sets a file descriptor to which a zero byte will be written whenever a C exception handler runs. I added a simple C API as well, PySignal_SetWakeupFd(fd). ........ r59575 | raymond.hettinger | 2007-12-19 23:14:34 +0100 (Wed, 19 Dec 2007) | 1 line Bigger range for non-extended opargs. ........ r59576 | guido.van.rossum | 2007-12-19 23:51:13 +0100 (Wed, 19 Dec 2007) | 5 lines Patch #1549 by Thomas Herve. This changes the rules for when __hash__ is inherited slightly, by allowing it to be inherited when one or more of __lt__, __le__, __gt__, __ge__ are overridden, as long as __eq__ and __ne__ aren't. ........ r59577 | raymond.hettinger | 2007-12-20 02:25:05 +0100 (Thu, 20 Dec 2007) | 1 line Add comments ........ r59578 | brett.cannon | 2007-12-20 11:09:52 +0100 (Thu, 20 Dec 2007) | 3 lines Add tests for the warnings module; specifically formatwarning and showwarning. Still need tests for warn_explicit and simplefilter. ........ r59582 | guido.van.rossum | 2007-12-20 18:28:10 +0100 (Thu, 20 Dec 2007) | 2 lines Patch #1672 by Joseph Armbruster. Use tempdir() to get a temporary directory. ........ r59584 | georg.brandl | 2007-12-20 22:03:02 +0100 (Thu, 20 Dec 2007) | 2 lines Fix refleak introduced in r59576. ........ r59586 | guido.van.rossum | 2007-12-21 00:48:28 +0100 (Fri, 21 Dec 2007) | 4 lines Improve performance of built-in any()/all() by avoiding PyIter_Next() -- using a trick found in ifilter(). Feel free to backport to 2.5. ........ r59591 | andrew.kuchling | 2007-12-22 18:27:02 +0100 (Sat, 22 Dec 2007) | 1 line Add item ........
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.. function:: set_wakeup_fd(fd)
Set the wakeup fd to *fd*. When a signal is received, a ``'\0'`` byte is
written to the fd. This can be used by a library to wakeup a poll or select
call, allowing the signal to be fully processed.
The old wakeup fd is returned. *fd* must be non-blocking. It is up to the
library to remove any bytes before calling poll or select again.
When threads are enabled, this function can only be called from the main thread;
attempting to call it from other threads will cause a :exc:`ValueError`
exception to be raised.
Merged revisions 60481,60485,60489-60492,60494-60496,60498-60499,60501-60503,60505-60506,60508-60509,60523-60524,60532,60543,60545,60547-60548,60552,60554,60556-60559,60561-60562,60569,60571-60572,60574,60576-60583,60585-60586,60589,60591,60594-60595,60597-60598,60600-60601,60606-60612,60615,60617,60619-60621,60623-60625,60627-60629,60631,60633,60635,60647,60650,60652,60654,60656,60658-60659,60664-60666,60668-60670,60672,60676,60678,60680-60683,60685-60686,60688,60690,60692-60694,60697-60700,60705-60706,60708,60711,60714,60720,60724-60730,60732,60736,60742,60744,60746,60748,60750-60751,60753,60756-60757,60759-60761,60763-60764,60766,60769-60770,60774-60784,60787-60789,60793,60796,60799-60809,60812-60813,60815-60821,60823-60826,60828-60829,60831-60834,60836,60838-60839,60846-60849,60852-60854,60856-60859,60861-60870,60874-60875,60880-60881,60886,60888-60890,60892,60894-60898,60900,60902-60906,60908,60911-60917,60919-60920,60922,60926,60929-60931,60933-60935,60937,60939-60941,60943-60954,60959-60961,60963-60964,60966-60967,60971,60977,60979-60989 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r60980 | georg.brandl | 2008-02-23 16:02:28 +0100 (Sat, 23 Feb 2008) | 2 lines #1492: allow overriding BaseHTTPServer's content type for error messages. ........ r60982 | georg.brandl | 2008-02-23 16:06:25 +0100 (Sat, 23 Feb 2008) | 2 lines #2165: fix test_logging failure on some machines. ........ r60983 | facundo.batista | 2008-02-23 16:07:35 +0100 (Sat, 23 Feb 2008) | 6 lines Issue 1089358. Adds the siginterrupt() function, that is just a wrapper around the system call with the same name. Also added test cases, doc changes and NEWS entry. Thanks Jason and Ralf Schmitt. ........ r60984 | georg.brandl | 2008-02-23 16:11:18 +0100 (Sat, 23 Feb 2008) | 2 lines #2067: file.__exit__() now calls subclasses' close() method. ........ r60985 | georg.brandl | 2008-02-23 16:19:54 +0100 (Sat, 23 Feb 2008) | 2 lines More difflib examples. Written for GHOP by Josip Dzolonga. ........ r60987 | andrew.kuchling | 2008-02-23 16:41:51 +0100 (Sat, 23 Feb 2008) | 1 line #2072: correct documentation for .rpc_paths ........ r60988 | georg.brandl | 2008-02-23 16:43:48 +0100 (Sat, 23 Feb 2008) | 2 lines #2161: Fix opcode name. ........ r60989 | andrew.kuchling | 2008-02-23 16:49:35 +0100 (Sat, 23 Feb 2008) | 2 lines #1119331: ncurses will just call exit() if the terminal name isn't found. Call setupterm() first so that we get a Python exception instead of just existing. ........
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.. function:: siginterrupt(signalnum, flag)
Change system call restart behaviour: if *flag* is :const:`False`, system calls
Merged revisions 61209-61214,61217-61222,61224-61226,61233-61237 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r61209 | georg.brandl | 2008-03-03 21:37:55 +0100 (Mon, 03 Mar 2008) | 2 lines There are now sixteen isfoo functions. ........ r61210 | georg.brandl | 2008-03-03 21:39:00 +0100 (Mon, 03 Mar 2008) | 2 lines 15 -> 16, the 2nd ........ r61211 | georg.brandl | 2008-03-03 22:22:47 +0100 (Mon, 03 Mar 2008) | 2 lines Actually import itertools. ........ r61212 | georg.brandl | 2008-03-03 22:31:50 +0100 (Mon, 03 Mar 2008) | 2 lines Expand a bit on genexp scopes. ........ r61213 | raymond.hettinger | 2008-03-03 23:04:55 +0100 (Mon, 03 Mar 2008) | 1 line Remove dependency on itertools -- a simple genexp suffices. ........ r61214 | raymond.hettinger | 2008-03-03 23:19:58 +0100 (Mon, 03 Mar 2008) | 1 line Issue 2226: Callable checked for the wrong abstract method. ........ r61217 | andrew.kuchling | 2008-03-04 01:40:32 +0100 (Tue, 04 Mar 2008) | 1 line Typo fix ........ r61218 | andrew.kuchling | 2008-03-04 02:30:10 +0100 (Tue, 04 Mar 2008) | 1 line Grammar fix; markup fix ........ r61219 | andrew.kuchling | 2008-03-04 02:47:38 +0100 (Tue, 04 Mar 2008) | 1 line Fix sentence fragment ........ r61220 | andrew.kuchling | 2008-03-04 02:48:26 +0100 (Tue, 04 Mar 2008) | 1 line Typo fix ........ r61221 | andrew.kuchling | 2008-03-04 02:49:37 +0100 (Tue, 04 Mar 2008) | 1 line Add versionadded tags ........ r61222 | andrew.kuchling | 2008-03-04 02:50:32 +0100 (Tue, 04 Mar 2008) | 1 line Thesis night results: add various items ........ r61224 | raymond.hettinger | 2008-03-04 05:17:08 +0100 (Tue, 04 Mar 2008) | 1 line Beef-up docs and tests for itertools. Fix-up end-case for product(). ........ r61225 | georg.brandl | 2008-03-04 08:25:54 +0100 (Tue, 04 Mar 2008) | 2 lines Fix some patch attributions. ........ r61226 | georg.brandl | 2008-03-04 08:33:30 +0100 (Tue, 04 Mar 2008) | 2 lines #2230: document that PyArg_* leaves addresses alone on error. ........ r61233 | neal.norwitz | 2008-03-04 17:22:46 +0100 (Tue, 04 Mar 2008) | 3 lines Close the file before trying to remove the directory so it works on Windows. As reported by Trent Nelson on python-dev. ........ r61234 | thomas.heller | 2008-03-04 21:09:11 +0100 (Tue, 04 Mar 2008) | 9 lines Merged changes from libffi3-branch. The bundled libffi copy is now in sync with the recently released libffi3.0.4 version, apart from some small changes to Modules/_ctypes/libffi/configure.ac. I gave up on using libffi3 files on os x. Instead, static configuration with files from pyobjc is used. ........ r61235 | thomas.heller | 2008-03-04 21:21:42 +0100 (Tue, 04 Mar 2008) | 1 line Try to fix the build for PY_LINUX. ........ r61236 | fred.drake | 2008-03-04 22:14:04 +0100 (Tue, 04 Mar 2008) | 2 lines fix typo ........ r61237 | raymond.hettinger | 2008-03-04 23:29:44 +0100 (Tue, 04 Mar 2008) | 1 line Fix refleak in chain(). ........
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will be restarted when interrupted by signal *signalnum*, otherwise system calls will
Merged revisions 60481,60485,60489-60492,60494-60496,60498-60499,60501-60503,60505-60506,60508-60509,60523-60524,60532,60543,60545,60547-60548,60552,60554,60556-60559,60561-60562,60569,60571-60572,60574,60576-60583,60585-60586,60589,60591,60594-60595,60597-60598,60600-60601,60606-60612,60615,60617,60619-60621,60623-60625,60627-60629,60631,60633,60635,60647,60650,60652,60654,60656,60658-60659,60664-60666,60668-60670,60672,60676,60678,60680-60683,60685-60686,60688,60690,60692-60694,60697-60700,60705-60706,60708,60711,60714,60720,60724-60730,60732,60736,60742,60744,60746,60748,60750-60751,60753,60756-60757,60759-60761,60763-60764,60766,60769-60770,60774-60784,60787-60789,60793,60796,60799-60809,60812-60813,60815-60821,60823-60826,60828-60829,60831-60834,60836,60838-60839,60846-60849,60852-60854,60856-60859,60861-60870,60874-60875,60880-60881,60886,60888-60890,60892,60894-60898,60900,60902-60906,60908,60911-60917,60919-60920,60922,60926,60929-60931,60933-60935,60937,60939-60941,60943-60954,60959-60961,60963-60964,60966-60967,60971,60977,60979-60989 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r60980 | georg.brandl | 2008-02-23 16:02:28 +0100 (Sat, 23 Feb 2008) | 2 lines #1492: allow overriding BaseHTTPServer's content type for error messages. ........ r60982 | georg.brandl | 2008-02-23 16:06:25 +0100 (Sat, 23 Feb 2008) | 2 lines #2165: fix test_logging failure on some machines. ........ r60983 | facundo.batista | 2008-02-23 16:07:35 +0100 (Sat, 23 Feb 2008) | 6 lines Issue 1089358. Adds the siginterrupt() function, that is just a wrapper around the system call with the same name. Also added test cases, doc changes and NEWS entry. Thanks Jason and Ralf Schmitt. ........ r60984 | georg.brandl | 2008-02-23 16:11:18 +0100 (Sat, 23 Feb 2008) | 2 lines #2067: file.__exit__() now calls subclasses' close() method. ........ r60985 | georg.brandl | 2008-02-23 16:19:54 +0100 (Sat, 23 Feb 2008) | 2 lines More difflib examples. Written for GHOP by Josip Dzolonga. ........ r60987 | andrew.kuchling | 2008-02-23 16:41:51 +0100 (Sat, 23 Feb 2008) | 1 line #2072: correct documentation for .rpc_paths ........ r60988 | georg.brandl | 2008-02-23 16:43:48 +0100 (Sat, 23 Feb 2008) | 2 lines #2161: Fix opcode name. ........ r60989 | andrew.kuchling | 2008-02-23 16:49:35 +0100 (Sat, 23 Feb 2008) | 2 lines #1119331: ncurses will just call exit() if the terminal name isn't found. Call setupterm() first so that we get a Python exception instead of just existing. ........
2008-02-23 12:23:06 -04:00
be interrupted. Returns nothing. Availability: Unix, Mac (see the man page
:manpage:`siginterrupt(3)` for further information).
Note that installing a signal handler with :func:`signal` will reset the restart
Merged revisions 61209-61214,61217-61222,61224-61226,61233-61237 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r61209 | georg.brandl | 2008-03-03 21:37:55 +0100 (Mon, 03 Mar 2008) | 2 lines There are now sixteen isfoo functions. ........ r61210 | georg.brandl | 2008-03-03 21:39:00 +0100 (Mon, 03 Mar 2008) | 2 lines 15 -> 16, the 2nd ........ r61211 | georg.brandl | 2008-03-03 22:22:47 +0100 (Mon, 03 Mar 2008) | 2 lines Actually import itertools. ........ r61212 | georg.brandl | 2008-03-03 22:31:50 +0100 (Mon, 03 Mar 2008) | 2 lines Expand a bit on genexp scopes. ........ r61213 | raymond.hettinger | 2008-03-03 23:04:55 +0100 (Mon, 03 Mar 2008) | 1 line Remove dependency on itertools -- a simple genexp suffices. ........ r61214 | raymond.hettinger | 2008-03-03 23:19:58 +0100 (Mon, 03 Mar 2008) | 1 line Issue 2226: Callable checked for the wrong abstract method. ........ r61217 | andrew.kuchling | 2008-03-04 01:40:32 +0100 (Tue, 04 Mar 2008) | 1 line Typo fix ........ r61218 | andrew.kuchling | 2008-03-04 02:30:10 +0100 (Tue, 04 Mar 2008) | 1 line Grammar fix; markup fix ........ r61219 | andrew.kuchling | 2008-03-04 02:47:38 +0100 (Tue, 04 Mar 2008) | 1 line Fix sentence fragment ........ r61220 | andrew.kuchling | 2008-03-04 02:48:26 +0100 (Tue, 04 Mar 2008) | 1 line Typo fix ........ r61221 | andrew.kuchling | 2008-03-04 02:49:37 +0100 (Tue, 04 Mar 2008) | 1 line Add versionadded tags ........ r61222 | andrew.kuchling | 2008-03-04 02:50:32 +0100 (Tue, 04 Mar 2008) | 1 line Thesis night results: add various items ........ r61224 | raymond.hettinger | 2008-03-04 05:17:08 +0100 (Tue, 04 Mar 2008) | 1 line Beef-up docs and tests for itertools. Fix-up end-case for product(). ........ r61225 | georg.brandl | 2008-03-04 08:25:54 +0100 (Tue, 04 Mar 2008) | 2 lines Fix some patch attributions. ........ r61226 | georg.brandl | 2008-03-04 08:33:30 +0100 (Tue, 04 Mar 2008) | 2 lines #2230: document that PyArg_* leaves addresses alone on error. ........ r61233 | neal.norwitz | 2008-03-04 17:22:46 +0100 (Tue, 04 Mar 2008) | 3 lines Close the file before trying to remove the directory so it works on Windows. As reported by Trent Nelson on python-dev. ........ r61234 | thomas.heller | 2008-03-04 21:09:11 +0100 (Tue, 04 Mar 2008) | 9 lines Merged changes from libffi3-branch. The bundled libffi copy is now in sync with the recently released libffi3.0.4 version, apart from some small changes to Modules/_ctypes/libffi/configure.ac. I gave up on using libffi3 files on os x. Instead, static configuration with files from pyobjc is used. ........ r61235 | thomas.heller | 2008-03-04 21:21:42 +0100 (Tue, 04 Mar 2008) | 1 line Try to fix the build for PY_LINUX. ........ r61236 | fred.drake | 2008-03-04 22:14:04 +0100 (Tue, 04 Mar 2008) | 2 lines fix typo ........ r61237 | raymond.hettinger | 2008-03-04 23:29:44 +0100 (Tue, 04 Mar 2008) | 1 line Fix refleak in chain(). ........
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behaviour to interruptible by implicitly calling :cfunc:`siginterrupt` with a true *flag*
Merged revisions 60481,60485,60489-60492,60494-60496,60498-60499,60501-60503,60505-60506,60508-60509,60523-60524,60532,60543,60545,60547-60548,60552,60554,60556-60559,60561-60562,60569,60571-60572,60574,60576-60583,60585-60586,60589,60591,60594-60595,60597-60598,60600-60601,60606-60612,60615,60617,60619-60621,60623-60625,60627-60629,60631,60633,60635,60647,60650,60652,60654,60656,60658-60659,60664-60666,60668-60670,60672,60676,60678,60680-60683,60685-60686,60688,60690,60692-60694,60697-60700,60705-60706,60708,60711,60714,60720,60724-60730,60732,60736,60742,60744,60746,60748,60750-60751,60753,60756-60757,60759-60761,60763-60764,60766,60769-60770,60774-60784,60787-60789,60793,60796,60799-60809,60812-60813,60815-60821,60823-60826,60828-60829,60831-60834,60836,60838-60839,60846-60849,60852-60854,60856-60859,60861-60870,60874-60875,60880-60881,60886,60888-60890,60892,60894-60898,60900,60902-60906,60908,60911-60917,60919-60920,60922,60926,60929-60931,60933-60935,60937,60939-60941,60943-60954,60959-60961,60963-60964,60966-60967,60971,60977,60979-60989 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r60980 | georg.brandl | 2008-02-23 16:02:28 +0100 (Sat, 23 Feb 2008) | 2 lines #1492: allow overriding BaseHTTPServer's content type for error messages. ........ r60982 | georg.brandl | 2008-02-23 16:06:25 +0100 (Sat, 23 Feb 2008) | 2 lines #2165: fix test_logging failure on some machines. ........ r60983 | facundo.batista | 2008-02-23 16:07:35 +0100 (Sat, 23 Feb 2008) | 6 lines Issue 1089358. Adds the siginterrupt() function, that is just a wrapper around the system call with the same name. Also added test cases, doc changes and NEWS entry. Thanks Jason and Ralf Schmitt. ........ r60984 | georg.brandl | 2008-02-23 16:11:18 +0100 (Sat, 23 Feb 2008) | 2 lines #2067: file.__exit__() now calls subclasses' close() method. ........ r60985 | georg.brandl | 2008-02-23 16:19:54 +0100 (Sat, 23 Feb 2008) | 2 lines More difflib examples. Written for GHOP by Josip Dzolonga. ........ r60987 | andrew.kuchling | 2008-02-23 16:41:51 +0100 (Sat, 23 Feb 2008) | 1 line #2072: correct documentation for .rpc_paths ........ r60988 | georg.brandl | 2008-02-23 16:43:48 +0100 (Sat, 23 Feb 2008) | 2 lines #2161: Fix opcode name. ........ r60989 | andrew.kuchling | 2008-02-23 16:49:35 +0100 (Sat, 23 Feb 2008) | 2 lines #1119331: ncurses will just call exit() if the terminal name isn't found. Call setupterm() first so that we get a Python exception instead of just existing. ........
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value for the given signal.
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.. function:: signal(signalnum, handler)
Set the handler for signal *signalnum* to the function *handler*. *handler* can
be a callable Python object taking two arguments (see below), or one of the
special values :const:`signal.SIG_IGN` or :const:`signal.SIG_DFL`. The previous
signal handler will be returned (see the description of :func:`getsignal`
above). (See the Unix man page :manpage:`signal(2)`.)
When threads are enabled, this function can only be called from the main thread;
attempting to call it from other threads will cause a :exc:`ValueError`
exception to be raised.
The *handler* is called with two arguments: the signal number and the current
stack frame (``None`` or a frame object; for a description of frame objects, see
the reference manual section on the standard type hierarchy or see the attribute
descriptions in the :mod:`inspect` module).
.. _signal-example:
Example
-------
Here is a minimal example program. It uses the :func:`alarm` function to limit
the time spent waiting to open a file; this is useful if the file is for a
serial device that may not be turned on, which would normally cause the
:func:`os.open` to hang indefinitely. The solution is to set a 5-second alarm
before opening the file; if the operation takes too long, the alarm signal will
be sent, and the handler raises an exception. ::
import signal, os
def handler(signum, frame):
print('Signal handler called with signal', signum)
raise IOError("Couldn't open device!")
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# Set the signal handler and a 5-second alarm
signal.signal(signal.SIGALRM, handler)
signal.alarm(5)
# This open() may hang indefinitely
fd = os.open('/dev/ttyS0', os.O_RDWR)
signal.alarm(0) # Disable the alarm