Name	Size	Mode	Actions
2to3.rst.txt	15898	0644	editdlrm
abc.rst.txt	11805	0644	editdlrm
aifc.rst.txt	7503	0644	editdlrm
allos.rst.txt	678	0644	editdlrm
archiving.rst.txt	440	0644	editdlrm
argparse.rst.txt	77480	0644	editdlrm
array.rst.txt	10812	0644	editdlrm
ast.rst.txt	10159	0644	editdlrm
asynchat.rst.txt	8528	0644	editdlrm
asyncio-dev.rst.txt	13398	0644	editdlrm
asyncio-eventloop.rst.txt	33701	0644	editdlrm
asyncio-eventloops.rst.txt	7660	0644	editdlrm
asyncio-protocol.rst.txt	25170	0644	editdlrm
asyncio-queue.rst.txt	4328	0644	editdlrm
asyncio-stream.rst.txt	14363	0644	editdlrm
asyncio-subprocess.rst.txt	15544	0644	editdlrm
asyncio-sync.rst.txt	9078	0644	editdlrm
asyncio-task.rst.txt	25406	0644	editdlrm
asyncio.rst.txt	2272	0644	editdlrm
asyncore.rst.txt	13624	0644	editdlrm
atexit.rst.txt	3669	0644	editdlrm
audioop.rst.txt	10712	0644	editdlrm
base64.rst.txt	10371	0644	editdlrm
bdb.rst.txt	12985	0644	editdlrm
binary.rst.txt	654	0644	editdlrm
binascii.rst.txt	6539	0644	editdlrm
binhex.rst.txt	1709	0644	editdlrm
bisect.rst.txt	5398	0644	editdlrm
builtins.rst.txt	1465	0644	editdlrm
bz2.rst.txt	8825	0644	editdlrm
calendar.rst.txt	10988	0644	editdlrm
cgi.rst.txt	22650	0644	editdlrm
cgitb.rst.txt	2918	0644	editdlrm
chunk.rst.txt	5094	0644	editdlrm
cmath.rst.txt	9326	0644	editdlrm
cmd.rst.txt	13795	0644	editdlrm
code.rst.txt	7817	0644	editdlrm
codecs.rst.txt	75564	0644	editdlrm
codeop.rst.txt	3021	0644	editdlrm
collections.abc.rst.txt	12861	0644	editdlrm
collections.rst.txt	46063	0644	editdlrm
colorsys.rst.txt	1820	0644	editdlrm
compileall.rst.txt	8975	0644	editdlrm
concurrency.rst.txt	673	0644	editdlrm
concurrent.futures.rst.txt	16910	0644	editdlrm
concurrent.rst.txt	171	0644	editdlrm
configparser.rst.txt	48756	0644	editdlrm
constants.rst.txt	3331	0644	editdlrm
contextlib.rst.txt	28175	0644	editdlrm
copy.rst.txt	3378	0644	editdlrm
copyreg.rst.txt	2182	0644	editdlrm
crypt.rst.txt	5122	0644	editdlrm
crypto.rst.txt	411	0644	editdlrm
csv.rst.txt	19902	0644	editdlrm
ctypes.rst.txt	88613	0644	editdlrm
curses.ascii.rst.txt	8920	0644	editdlrm
curses.panel.rst.txt	2764	0644	editdlrm
curses.rst.txt	76397	0644	editdlrm
custominterp.rst.txt	569	0644	editdlrm
datatypes.rst.txt	751	0644	editdlrm
datetime.rst.txt	90524	0644	editdlrm
dbm.rst.txt	14293	0644	editdlrm
debug.rst.txt	471	0644	editdlrm
decimal.rst.txt	74869	0644	editdlrm
development.rst.txt	704	0644	editdlrm
difflib.rst.txt	29861	0644	editdlrm
dis.rst.txt	32567	0644	editdlrm
distribution.rst.txt	452	0644	editdlrm
distutils.rst.txt	1974	0644	editdlrm
doctest.rst.txt	71743	0644	editdlrm
dummy_threading.rst.txt	784	0644	editdlrm
email.charset.rst.txt	9293	0644	editdlrm
email.compat32-message.rst.txt	33493	0644	editdlrm
email.contentmanager.rst.txt	9112	0644	editdlrm
email.encoders.rst.txt	2715	0644	editdlrm
email.errors.rst.txt	4792	0644	editdlrm
email.examples.rst.txt	1915	0644	editdlrm
email.generator.rst.txt	13637	0644	editdlrm
email.header.rst.txt	9188	0644	editdlrm
email.headerregistry.rst.txt	17957	0644	editdlrm
email.iterators.rst.txt	2795	0644	editdlrm
email.message.rst.txt	33008	0644	editdlrm
email.mime.rst.txt	11721	0644	editdlrm
email.parser.rst.txt	14092	0644	editdlrm
email.policy.rst.txt	27022	0644	editdlrm
email.rst.txt	6785	0644	editdlrm
email.util.rst.txt	9214	0644	editdlrm
ensurepip.rst.txt	4987	0644	editdlrm
enum.rst.txt	32751	0644	editdlrm
errno.rst.txt	6811	0644	editdlrm
exceptions.rst.txt	25570	0644	editdlrm
faulthandler.rst.txt	6136	0644	editdlrm
fcntl.rst.txt	7152	0644	editdlrm
filecmp.rst.txt	5623	0644	editdlrm
fileformats.rst.txt	287	0644	editdlrm
fileinput.rst.txt	8051	0644	editdlrm
filesys.rst.txt	961	0644	editdlrm
fnmatch.rst.txt	3103	0644	editdlrm
formatter.rst.txt	13242	0644	editdlrm
fpectl.rst.txt	4180	0644	editdlrm
fractions.rst.txt	6364	0644	editdlrm
frameworks.rst.txt	391	0644	editdlrm
ftplib.rst.txt	17552	0644	editdlrm
functional.rst.txt	365	0644	editdlrm
functions.rst.txt	71621	0644	editdlrm
functools.rst.txt	18503	0644	editdlrm
gc.rst.txt	9694	0644	editdlrm
getopt.rst.txt	6557	0644	editdlrm
getpass.rst.txt	1882	0644	editdlrm
gettext.rst.txt	25588	0644	editdlrm
glob.rst.txt	3508	0644	editdlrm
grp.rst.txt	2417	0644	editdlrm
gzip.rst.txt	8301	0644	editdlrm
hashlib.rst.txt	26523	0644	editdlrm
heapq.rst.txt	13402	0644	editdlrm
hmac.rst.txt	4020	0644	editdlrm
html.entities.rst.txt	1319	0644	editdlrm
html.parser.rst.txt	11275	0644	editdlrm
html.rst.txt	1304	0644	editdlrm
http.client.rst.txt	18870	0644	editdlrm
http.cookiejar.rst.txt	27832	0644	editdlrm
http.cookies.rst.txt	8645	0644	editdlrm
http.rst.txt	7096	0644	editdlrm
http.server.rst.txt	17639	0644	editdlrm
i18n.rst.txt	408	0644	editdlrm
idle.rst.txt	25834	0644	editdlrm
imaplib.rst.txt	20367	0644	editdlrm
imghdr.rst.txt	2938	0644	editdlrm
imp.rst.txt	15548	0644	editdlrm
importlib.rst.txt	53563	0644	editdlrm
index.rst.txt	2258	0644	editdlrm
inspect.rst.txt	53928	0644	editdlrm
internet.rst.txt	992	0644	editdlrm
intro.rst.txt	2645	0644	editdlrm
io.rst.txt	40328	0644	editdlrm
ipaddress.rst.txt	32340	0644	editdlrm
ipc.rst.txt	649	0644	editdlrm
itertools.rst.txt	38459	0644	editdlrm
json.rst.txt	27876	0644	editdlrm
keyword.rst.txt	617	0644	editdlrm
language.rst.txt	522	0644	editdlrm
linecache.rst.txt	2408	0644	editdlrm
locale.rst.txt	25470	0644	editdlrm
logging.config.rst.txt	33886	0644	editdlrm
logging.handlers.rst.txt	42497	0644	editdlrm
logging.rst.txt	60479	0644	editdlrm
lzma.rst.txt	17361	0644	editdlrm
macpath.rst.txt	707	0644	editdlrm
mailbox.rst.txt	63055	0644	editdlrm
mailcap.rst.txt	3691	0644	editdlrm
markup.rst.txt	679	0644	editdlrm
marshal.rst.txt	4855	0644	editdlrm
math.rst.txt	14375	0644	editdlrm
mimetypes.rst.txt	9839	0644	editdlrm
misc.rst.txt	247	0644	editdlrm
mm.rst.txt	431	0644	editdlrm
mmap.rst.txt	11232	0644	editdlrm
modulefinder.rst.txt	3240	0644	editdlrm
modules.rst.txt	355	0644	editdlrm
msilib.rst.txt	18612	0644	editdlrm
msvcrt.rst.txt	4392	0644	editdlrm
multiprocessing.rst.txt	104494	0644	editdlrm
netdata.rst.txt	339	0644	editdlrm
netrc.rst.txt	3007	0644	editdlrm
nis.rst.txt	1993	0644	editdlrm
nntplib.rst.txt	21821	0644	editdlrm
numbers.rst.txt	8089	0644	editdlrm
numeric.rst.txt	696	0644	editdlrm
operator.rst.txt	18989	0644	editdlrm
optparse.rst.txt	76996	0644	editdlrm
os.path.rst.txt	16419	0644	editdlrm
os.rst.txt	137534	0644	editdlrm
ossaudiodev.rst.txt	17845	0644	editdlrm
othergui.rst.txt	2822	0644	editdlrm
parser.rst.txt	15148	0644	editdlrm
pathlib.rst.txt	30045	0644	editdlrm
pdb.rst.txt	19454	0644	editdlrm
persistence.rst.txt	591	0644	editdlrm
pickle.rst.txt	37440	0644	editdlrm
pickletools.rst.txt	3729	0644	editdlrm
pipes.rst.txt	2557	0644	editdlrm
pkgutil.rst.txt	8730	0644	editdlrm
platform.rst.txt	9624	0644	editdlrm
plistlib.rst.txt	7398	0644	editdlrm
poplib.rst.txt	8197	0644	editdlrm
posix.rst.txt	3694	0644	editdlrm
pprint.rst.txt	14274	0644	editdlrm
profile.rst.txt	27969	0644	editdlrm
pty.rst.txt	3123	0644	editdlrm
pwd.rst.txt	2739	0644	editdlrm
pyclbr.rst.txt	3297	0644	editdlrm
pydoc.rst.txt	4688	0644	editdlrm
pyexpat.rst.txt	28620	0644	editdlrm
python.rst.txt	475	0644	editdlrm
py_compile.rst.txt	3851	0644	editdlrm
queue.rst.txt	7268	0644	editdlrm
quopri.rst.txt	2571	0644	editdlrm
random.rst.txt	18503	0644	editdlrm
re.rst.txt	64936	0644	editdlrm
readline.rst.txt	11943	0644	editdlrm
reprlib.rst.txt	5162	0644	editdlrm
resource.rst.txt	12291	0644	editdlrm
rlcompleter.rst.txt	2294	0644	editdlrm
runpy.rst.txt	8285	0644	editdlrm
sched.rst.txt	4842	0644	editdlrm
secrets.rst.txt	5930	0644	editdlrm
select.rst.txt	28175	0644	editdlrm
selectors.rst.txt	8925	0644	editdlrm
shelve.rst.txt	8390	0644	editdlrm
shlex.rst.txt	16441	0644	editdlrm
shutil.rst.txt	26014	0644	editdlrm
signal.rst.txt	17218	0644	editdlrm
site.rst.txt	9628	0644	editdlrm
smtpd.rst.txt	10806	0644	editdlrm
smtplib.rst.txt	23439	0644	editdlrm
sndhdr.rst.txt	1994	0644	editdlrm
socket.rst.txt	68202	0644	editdlrm
socketserver.rst.txt	23712	0644	editdlrm
spwd.rst.txt	2958	0644	editdlrm
sqlite3.rst.txt	39215	0644	editdlrm
ssl.rst.txt	96021	0644	editdlrm
stat.rst.txt	9805	0644	editdlrm
statistics.rst.txt	15301	0644	editdlrm
stdtypes.rst.txt	179240	0644	editdlrm
string.rst.txt	35374	0644	editdlrm
stringprep.rst.txt	4279	0644	editdlrm
struct.rst.txt	19581	0644	editdlrm
subprocess.rst.txt	45793	0644	editdlrm
sunau.rst.txt	7390	0644	editdlrm
superseded.rst.txt	258	0644	editdlrm
symbol.rst.txt	975	0644	editdlrm
symtable.rst.txt	4964	0644	editdlrm
sys.rst.txt	58273	0644	editdlrm
sysconfig.rst.txt	8749	0644	editdlrm
syslog.rst.txt	4302	0644	editdlrm
tabnanny.rst.txt	2007	0644	editdlrm
tarfile.rst.txt	31749	0644	editdlrm
telnetlib.rst.txt	7899	0644	editdlrm
tempfile.rst.txt	13857	0644	editdlrm
termios.rst.txt	3751	0644	editdlrm
test.rst.txt	25764	0644	editdlrm
text.rst.txt	584	0644	editdlrm
textwrap.rst.txt	10519	0644	editdlrm
threading.rst.txt	39257	0644	editdlrm
time.rst.txt	32967	0644	editdlrm
timeit.rst.txt	13000	0644	editdlrm
tk.rst.txt	1639	0644	editdlrm
tkinter.rst.txt	33027	0644	editdlrm
tkinter.scrolledtext.rst.txt	1255	0644	editdlrm
tkinter.tix.rst.txt	22653	0644	editdlrm
tkinter.ttk.rst.txt	58489	0644	editdlrm
token.rst.txt	2607	0644	editdlrm
tokenize.rst.txt	10002	0644	editdlrm
trace.rst.txt	6914	0644	editdlrm
traceback.rst.txt	17854	0644	editdlrm
tracemalloc.rst.txt	22089	0644	editdlrm
tty.rst.txt	1097	0644	editdlrm
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typing.rst.txt	34332	0644	editdlrm
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unittest.mock-examples.rst.txt	46206	0644	editdlrm
unittest.mock.rst.txt	85991	0644	editdlrm
unittest.rst.txt	93304	0644	editdlrm
unix.rst.txt	446	0644	editdlrm
urllib.error.rst.txt	2199	0644	editdlrm
urllib.parse.rst.txt	27332	0644	editdlrm
urllib.request.rst.txt	59360	0644	editdlrm
urllib.robotparser.rst.txt	2969	0644	editdlrm
urllib.rst.txt	466	0644	editdlrm
uu.rst.txt	2387	0644	editdlrm
uuid.rst.txt	8760	0644	editdlrm
venv.rst.txt	20621	0644	editdlrm
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wave.rst.txt	6870	0644	editdlrm
weakref.rst.txt	21328	0644	editdlrm
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winreg.rst.txt	24073	0644	editdlrm
winsound.rst.txt	5134	0644	editdlrm
wsgiref.rst.txt	33047	0644	editdlrm
xdrlib.rst.txt	8078	0644	editdlrm
xml.dom.minidom.rst.txt	10198	0644	editdlrm
xml.dom.pulldom.rst.txt	5186	0644	editdlrm
xml.dom.rst.txt	39507	0644	editdlrm
xml.etree.elementtree.rst.txt	43871	0644	editdlrm
xml.rst.txt	6071	0644	editdlrm
xml.sax.handler.rst.txt	15399	0644	editdlrm
xml.sax.reader.rst.txt	12133	0644	editdlrm
xml.sax.rst.txt	7159	0644	editdlrm
xml.sax.utils.rst.txt	3901	0644	editdlrm
xmlrpc.client.rst.txt	23071	0644	editdlrm
xmlrpc.rst.txt	475	0644	editdlrm
xmlrpc.server.rst.txt	14990	0644	editdlrm
zipapp.rst.txt	17392	0644	editdlrm
zipfile.rst.txt	24005	0644	editdlrm
zipimport.rst.txt	5805	0644	editdlrm
zlib.rst.txt	13912	0644	editdlrm
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__future__.rst.txt	5245	0644	editdlrm
__main__.rst.txt	904	0644	editdlrm

: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. General rules ------------- The :func:`signal.signal` function allows defining custom handlers to be executed when a signal is received. A small number of default handlers are installed: :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. 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. Execution of Python signal handlers ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ A Python signal handler does not get executed inside the low-level (C) signal handler. Instead, the low-level signal handler sets a flag which tells the :term:`virtual machine` to execute the corresponding Python signal handler at a later point(for example at the next :term:`bytecode` instruction). This has consequences: * It makes little sense to catch synchronous errors like :const:`SIGFPE` or :const:`SIGSEGV` that are caused by an invalid operation in C code. Python will return from the signal handler to the C code, which is likely to raise the same signal again, causing Python to apparently hang. From Python 3.3 onwards, you can use the :mod:`faulthandler` module to report on synchronous errors. * A long-running calculation implemented purely in C (such as regular expression matching on a large body of text) may run uninterrupted for an arbitrary amount of time, regardless of any signals received. The Python signal handlers will be called when the calculation finishes. .. _signals-and-threads: Signals and threads ^^^^^^^^^^^^^^^^^^^ Python signal handlers are always executed in the main Python thread, even if the signal was received in another thread. This means that signals can't be used as a means of inter-thread communication. You can use the synchronization primitives from the :mod:`threading` module instead. Besides, only the main thread is allowed to set a new signal handler. Module contents --------------- .. versionchanged:: 3.5 signal (SIG*), handler (:const:`SIG_DFL`, :const:`SIG_IGN`) and sigmask (:const:`SIG_BLOCK`, :const:`SIG_UNBLOCK`, :const:`SIG_SETMASK`) related constants listed below were turned into :class:`enums `. :func:`getsignal`, :func:`pthread_sigmask`, :func:`sigpending` and :func:`sigwait` functions return human-readable :class:`enums `. 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:`SIGCHLD` 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 ````. The Unix man page for ':c:func:`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:: CTRL_C_EVENT The signal corresponding to the :kbd:`Ctrl+C` keystroke event. This signal can only be used with :func:`os.kill`. Availability: Windows. .. versionadded:: 3.2 .. data:: CTRL_BREAK_EVENT The signal corresponding to the :kbd:`Ctrl+Break` keystroke event. This signal can only be used with :func:`os.kill`. Availability: Windows. .. versionadded:: 3.2 .. data:: NSIG One more than the number of the highest signal number. .. data:: ITIMER_REAL 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. .. data:: SIG_BLOCK A possible value for the *how* parameter to :func:`pthread_sigmask` indicating that signals are to be blocked. .. versionadded:: 3.3 .. data:: SIG_UNBLOCK A possible value for the *how* parameter to :func:`pthread_sigmask` indicating that signals are to be unblocked. .. versionadded:: 3.3 .. data:: SIG_SETMASK A possible value for the *how* parameter to :func:`pthread_sigmask` indicating that the signal mask is to be replaced. .. versionadded:: 3.3 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:`OSError`. .. versionadded:: 3.3 This error used to be a subtype of :exc:`IOError`, which is now an alias of :exc:`OSError`. 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)`.) See also :func:`sigwait`, :func:`sigwaitinfo`, :func:`sigtimedwait` and :func:`sigpending`. .. function:: pthread_kill(thread_id, signalnum) Send the signal *signalnum* to the thread *thread_id*, another thread in the same process as the caller. The target thread can be executing any code (Python or not). However, if the target thread is executing the Python interpreter, the Python signal handlers will be :ref:`executed by the main thread `. Therefore, the only point of sending a signal to a particular Python thread would be to force a running system call to fail with :exc:`InterruptedError`. Use :func:`threading.get_ident()` or the :attr:`~threading.Thread.ident` attribute of :class:`threading.Thread` objects to get a suitable value for *thread_id*. If *signalnum* is 0, then no signal is sent, but error checking is still performed; this can be used to check if the target thread is still running. Availability: Unix (see the man page :manpage:`pthread_kill(3)` for further information). See also :func:`os.kill`. .. versionadded:: 3.3 .. function:: pthread_sigmask(how, mask) Fetch and/or change the signal mask of the calling thread. The signal mask is the set of signals whose delivery is currently blocked for the caller. Return the old signal mask as a set of signals. The behavior of the call is dependent on the value of *how*, as follows. * :data:`SIG_BLOCK`: The set of blocked signals is the union of the current set and the *mask* argument. * :data:`SIG_UNBLOCK`: The signals in *mask* are removed from the current set of blocked signals. It is permissible to attempt to unblock a signal which is not blocked. * :data:`SIG_SETMASK`: The set of blocked signals is set to the *mask* argument. *mask* is a set of signal numbers (e.g. {:const:`signal.SIGINT`, :const:`signal.SIGTERM`}). Use ``range(1, signal.NSIG)`` for a full mask including all signals. For example, ``signal.pthread_sigmask(signal.SIG_BLOCK, [])`` reads the signal mask of the calling thread. Availability: Unix. See the man page :manpage:`sigprocmask(3)` and :manpage:`pthread_sigmask(3)` for further information. See also :func:`pause`, :func:`sigpending` and :func:`sigwait`. .. versionadded:: 3.3 .. function:: setitimer(which, seconds[, interval]) 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. 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 an :exc:`ItimerError`. Availability: Unix. .. function:: getitimer(which) Returns current value of a given interval timer specified by *which*. Availability: Unix. .. function:: set_wakeup_fd(fd) Set the wakeup file descriptor to *fd*. When a signal is received, the signal number is written as a single byte into 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 (or -1 if file descriptor wakeup was not enabled). If *fd* is -1, file descriptor wakeup is disabled. If not -1, *fd* must be non-blocking. It is up to the library to remove any bytes from *fd* before calling poll or select again. Use for example ``struct.unpack('%uB' % len(data), data)`` to decode the signal numbers list. 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. .. versionchanged:: 3.5 On Windows, the function now also supports socket handles. .. function:: siginterrupt(signalnum, flag) Change system call restart behaviour: if *flag* is :const:`False`, system calls will be restarted when interrupted by signal *signalnum*, otherwise system calls will be interrupted. Returns nothing. Availability: Unix (see the man page :manpage:`siginterrupt(3)` for further information). Note that installing a signal handler with :func:`signal` will reset the restart behaviour to interruptible by implicitly calling :c:func:`siginterrupt` with a true *flag* value for the given signal. .. 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 :ref:`description in the type hierarchy ` or see the attribute descriptions in the :mod:`inspect` module). On Windows, :func:`signal` can only be called with :const:`SIGABRT`, :const:`SIGFPE`, :const:`SIGILL`, :const:`SIGINT`, :const:`SIGSEGV`, :const:`SIGTERM`, or :const:`SIGBREAK`. A :exc:`ValueError` will be raised in any other case. Note that not all systems define the same set of signal names; an :exc:`AttributeError` will be raised if a signal name is not defined as ``SIG*`` module level constant. .. function:: sigpending() Examine the set of signals that are pending for delivery to the calling thread (i.e., the signals which have been raised while blocked). Return the set of the pending signals. Availability: Unix (see the man page :manpage:`sigpending(2)` for further information). See also :func:`pause`, :func:`pthread_sigmask` and :func:`sigwait`. .. versionadded:: 3.3 .. function:: sigwait(sigset) Suspend execution of the calling thread until the delivery of one of the signals specified in the signal set *sigset*. The function accepts the signal (removes it from the pending list of signals), and returns the signal number. Availability: Unix (see the man page :manpage:`sigwait(3)` for further information). See also :func:`pause`, :func:`pthread_sigmask`, :func:`sigpending`, :func:`sigwaitinfo` and :func:`sigtimedwait`. .. versionadded:: 3.3 .. function:: sigwaitinfo(sigset) Suspend execution of the calling thread until the delivery of one of the signals specified in the signal set *sigset*. The function accepts the signal and removes it from the pending list of signals. If one of the signals in *sigset* is already pending for the calling thread, the function will return immediately with information about that signal. The signal handler is not called for the delivered signal. The function raises an :exc:`InterruptedError` if it is interrupted by a signal that is not in *sigset*. The return value is an object representing the data contained in the :c:type:`siginfo_t` structure, namely: :attr:`si_signo`, :attr:`si_code`, :attr:`si_errno`, :attr:`si_pid`, :attr:`si_uid`, :attr:`si_status`, :attr:`si_band`. Availability: Unix (see the man page :manpage:`sigwaitinfo(2)` for further information). See also :func:`pause`, :func:`sigwait` and :func:`sigtimedwait`. .. versionadded:: 3.3 .. versionchanged:: 3.5 The function is now retried if interrupted by a signal not in *sigset* and the signal handler does not raise an exception (see :pep:`475` for the rationale). .. function:: sigtimedwait(sigset, timeout) Like :func:`sigwaitinfo`, but takes an additional *timeout* argument specifying a timeout. If *timeout* is specified as :const:`0`, a poll is performed. Returns :const:`None` if a timeout occurs. Availability: Unix (see the man page :manpage:`sigtimedwait(2)` for further information). See also :func:`pause`, :func:`sigwait` and :func:`sigwaitinfo`. .. versionadded:: 3.3 .. versionchanged:: 3.5 The function is now retried with the recomputed *timeout* if interrupted by a signal not in *sigset* and the signal handler does not raise an exception (see :pep:`475` for the rationale). .. _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 OSError("Couldn't open device!") # 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