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Georg Brandl116aa622007-08-15 14:28:22 +00001
2:mod:`time` --- Time access and conversions
3===========================================
4
5.. module:: time
6 :synopsis: Time access and conversions.
7
8
9This module provides various time-related functions. For related
10functionality, see also the :mod:`datetime` and :mod:`calendar` modules.
11
12Although this module is always available,
13not all functions are available on all platforms. Most of the functions
14defined in this module call platform C library functions with the same name. It
15may sometimes be helpful to consult the platform documentation, because the
16semantics of these functions varies among platforms.
17
18An explanation of some terminology and conventions is in order.
19
20 .. index:: single: epoch
21
22* The :dfn:`epoch` is the point where the time starts. On January 1st of that
23 year, at 0 hours, the "time since the epoch" is zero. For Unix, the epoch is
24 1970. To find out what the epoch is, look at ``gmtime(0)``.
25
26 .. index:: single: Year 2038
27
28* The functions in this module do not handle dates and times before the epoch or
29 far in the future. The cut-off point in the future is determined by the C
30 library; for Unix, it is typically in 2038.
31
32 .. index::
33 single: Year 2000
34 single: Y2K
35
36* **Year 2000 (Y2K) issues**: Python depends on the platform's C library, which
37 generally doesn't have year 2000 issues, since all dates and times are
38 represented internally as seconds since the epoch. Functions accepting a
39 :class:`struct_time` (see below) generally require a 4-digit year. For backward
40 compatibility, 2-digit years are supported if the module variable
41 ``accept2dyear`` is a non-zero integer; this variable is initialized to ``1``
42 unless the environment variable :envvar:`PYTHONY2K` is set to a non-empty
43 string, in which case it is initialized to ``0``. Thus, you can set
44 :envvar:`PYTHONY2K` to a non-empty string in the environment to require 4-digit
45 years for all year input. When 2-digit years are accepted, they are converted
46 according to the POSIX or X/Open standard: values 69-99 are mapped to 1969-1999,
47 and values 0--68 are mapped to 2000--2068. Values 100--1899 are always illegal.
48 Note that this is new as of Python 1.5.2(a2); earlier versions, up to Python
49 1.5.1 and 1.5.2a1, would add 1900 to year values below 1900.
50
51 .. index::
52 single: UTC
53 single: Coordinated Universal Time
54 single: Greenwich Mean Time
55
56* UTC is Coordinated Universal Time (formerly known as Greenwich Mean Time, or
57 GMT). The acronym UTC is not a mistake but a compromise between English and
58 French.
59
60 .. index:: single: Daylight Saving Time
61
62* DST is Daylight Saving Time, an adjustment of the timezone by (usually) one
63 hour during part of the year. DST rules are magic (determined by local law) and
64 can change from year to year. The C library has a table containing the local
65 rules (often it is read from a system file for flexibility) and is the only
66 source of True Wisdom in this respect.
67
68* The precision of the various real-time functions may be less than suggested by
69 the units in which their value or argument is expressed. E.g. on most Unix
70 systems, the clock "ticks" only 50 or 100 times a second, and on the Mac, times
71 are only accurate to whole seconds.
72
73* On the other hand, the precision of :func:`time` and :func:`sleep` is better
74 than their Unix equivalents: times are expressed as floating point numbers,
75 :func:`time` returns the most accurate time available (using Unix
76 :cfunc:`gettimeofday` where available), and :func:`sleep` will accept a time
77 with a nonzero fraction (Unix :cfunc:`select` is used to implement this, where
78 available).
79
80* The time value as returned by :func:`gmtime`, :func:`localtime`, and
81 :func:`strptime`, and accepted by :func:`asctime`, :func:`mktime` and
82 :func:`strftime`, is a sequence of 9 integers. The return values of
83 :func:`gmtime`, :func:`localtime`, and :func:`strptime` also offer attribute
84 names for individual fields.
85
86 +-------+------------------+------------------------------+
87 | Index | Attribute | Values |
88 +=======+==================+==============================+
89 | 0 | :attr:`tm_year` | (for example, 1993) |
90 +-------+------------------+------------------------------+
91 | 1 | :attr:`tm_mon` | range [1,12] |
92 +-------+------------------+------------------------------+
93 | 2 | :attr:`tm_mday` | range [1,31] |
94 +-------+------------------+------------------------------+
95 | 3 | :attr:`tm_hour` | range [0,23] |
96 +-------+------------------+------------------------------+
97 | 4 | :attr:`tm_min` | range [0,59] |
98 +-------+------------------+------------------------------+
99 | 5 | :attr:`tm_sec` | range [0,61]; see **(1)** in |
100 | | | :func:`strftime` description |
101 +-------+------------------+------------------------------+
102 | 6 | :attr:`tm_wday` | range [0,6], Monday is 0 |
103 +-------+------------------+------------------------------+
104 | 7 | :attr:`tm_yday` | range [1,366] |
105 +-------+------------------+------------------------------+
106 | 8 | :attr:`tm_isdst` | 0, 1 or -1; see below |
107 +-------+------------------+------------------------------+
108
109 Note that unlike the C structure, the month value is a range of 1-12, not 0-11.
110 A year value will be handled as described under "Year 2000 (Y2K) issues" above.
111 A ``-1`` argument as the daylight savings flag, passed to :func:`mktime` will
112 usually result in the correct daylight savings state to be filled in.
113
114 When a tuple with an incorrect length is passed to a function expecting a
115 :class:`struct_time`, or having elements of the wrong type, a :exc:`TypeError`
116 is raised.
117
Georg Brandl116aa622007-08-15 14:28:22 +0000118The module defines the following functions and data items:
119
120
121.. data:: accept2dyear
122
123 Boolean value indicating whether two-digit year values will be accepted. This
124 is true by default, but will be set to false if the environment variable
125 :envvar:`PYTHONY2K` has been set to a non-empty string. It may also be modified
126 at run time.
127
128
129.. data:: altzone
130
131 The offset of the local DST timezone, in seconds west of UTC, if one is defined.
132 This is negative if the local DST timezone is east of UTC (as in Western Europe,
133 including the UK). Only use this if ``daylight`` is nonzero.
134
135
136.. function:: asctime([t])
137
138 Convert a tuple or :class:`struct_time` representing a time as returned by
139 :func:`gmtime` or :func:`localtime` to a 24-character string of the following
140 form: ``'Sun Jun 20 23:21:05 1993'``. If *t* is not provided, the current time
141 as returned by :func:`localtime` is used. Locale information is not used by
142 :func:`asctime`.
143
144 .. note::
145
146 Unlike the C function of the same name, there is no trailing newline.
147
Georg Brandl116aa622007-08-15 14:28:22 +0000148
149.. function:: clock()
150
151 .. index::
152 single: CPU time
153 single: processor time
154 single: benchmarking
155
156 On Unix, return the current processor time as a floating point number expressed
157 in seconds. The precision, and in fact the very definition of the meaning of
158 "processor time", depends on that of the C function of the same name, but in any
159 case, this is the function to use for benchmarking Python or timing algorithms.
160
161 On Windows, this function returns wall-clock seconds elapsed since the first
162 call to this function, as a floating point number, based on the Win32 function
163 :cfunc:`QueryPerformanceCounter`. The resolution is typically better than one
164 microsecond.
165
166
167.. function:: ctime([secs])
168
169 Convert a time expressed in seconds since the epoch to a string representing
170 local time. If *secs* is not provided or :const:`None`, the current time as
171 returned by :func:`time` is used. ``ctime(secs)`` is equivalent to
172 ``asctime(localtime(secs))``. Locale information is not used by :func:`ctime`.
173
Georg Brandl116aa622007-08-15 14:28:22 +0000174
175.. data:: daylight
176
177 Nonzero if a DST timezone is defined.
178
179
180.. function:: gmtime([secs])
181
182 Convert a time expressed in seconds since the epoch to a :class:`struct_time` in
183 UTC in which the dst flag is always zero. If *secs* is not provided or
184 :const:`None`, the current time as returned by :func:`time` is used. Fractions
185 of a second are ignored. See above for a description of the
186 :class:`struct_time` object. See :func:`calendar.timegm` for the inverse of this
187 function.
188
Georg Brandl116aa622007-08-15 14:28:22 +0000189
190.. function:: localtime([secs])
191
192 Like :func:`gmtime` but converts to local time. If *secs* is not provided or
193 :const:`None`, the current time as returned by :func:`time` is used. The dst
194 flag is set to ``1`` when DST applies to the given time.
195
Georg Brandl116aa622007-08-15 14:28:22 +0000196
197.. function:: mktime(t)
198
199 This is the inverse function of :func:`localtime`. Its argument is the
200 :class:`struct_time` or full 9-tuple (since the dst flag is needed; use ``-1``
201 as the dst flag if it is unknown) which expresses the time in *local* time, not
202 UTC. It returns a floating point number, for compatibility with :func:`time`.
203 If the input value cannot be represented as a valid time, either
204 :exc:`OverflowError` or :exc:`ValueError` will be raised (which depends on
205 whether the invalid value is caught by Python or the underlying C libraries).
206 The earliest date for which it can generate a time is platform-dependent.
207
208
209.. function:: sleep(secs)
210
211 Suspend execution for the given number of seconds. The argument may be a
212 floating point number to indicate a more precise sleep time. The actual
213 suspension time may be less than that requested because any caught signal will
214 terminate the :func:`sleep` following execution of that signal's catching
215 routine. Also, the suspension time may be longer than requested by an arbitrary
216 amount because of the scheduling of other activity in the system.
217
218
219.. function:: strftime(format[, t])
220
221 Convert a tuple or :class:`struct_time` representing a time as returned by
222 :func:`gmtime` or :func:`localtime` to a string as specified by the *format*
223 argument. If *t* is not provided, the current time as returned by
224 :func:`localtime` is used. *format* must be a string. :exc:`ValueError` is
225 raised if any field in *t* is outside of the allowed range.
226
Georg Brandl55ac8f02007-09-01 13:51:09 +0000227 0 is a legal argument for any position in the time tuple; if it is normally
228 illegal the value is forced to a correct one.
Georg Brandl116aa622007-08-15 14:28:22 +0000229
230 The following directives can be embedded in the *format* string. They are shown
231 without the optional field width and precision specification, and are replaced
232 by the indicated characters in the :func:`strftime` result:
233
Georg Brandl55ac8f02007-09-01 13:51:09 +0000234 +-----------+------------------------------------------------+-------+
235 | Directive | Meaning | Notes |
236 +===========+================================================+=======+
237 | ``%a`` | Locale's abbreviated weekday name. | |
238 | | | |
239 +-----------+------------------------------------------------+-------+
240 | ``%A`` | Locale's full weekday name. | |
241 +-----------+------------------------------------------------+-------+
242 | ``%b`` | Locale's abbreviated month name. | |
243 | | | |
244 +-----------+------------------------------------------------+-------+
245 | ``%B`` | Locale's full month name. | |
246 +-----------+------------------------------------------------+-------+
247 | ``%c`` | Locale's appropriate date and time | |
248 | | representation. | |
249 +-----------+------------------------------------------------+-------+
250 | ``%d`` | Day of the month as a decimal number [01,31]. | |
251 | | | |
252 +-----------+------------------------------------------------+-------+
253 | ``%H`` | Hour (24-hour clock) as a decimal number | |
254 | | [00,23]. | |
255 +-----------+------------------------------------------------+-------+
256 | ``%I`` | Hour (12-hour clock) as a decimal number | |
257 | | [01,12]. | |
258 +-----------+------------------------------------------------+-------+
259 | ``%j`` | Day of the year as a decimal number [001,366]. | |
260 | | | |
261 +-----------+------------------------------------------------+-------+
262 | ``%m`` | Month as a decimal number [01,12]. | |
263 | | | |
264 +-----------+------------------------------------------------+-------+
265 | ``%M`` | Minute as a decimal number [00,59]. | |
266 | | | |
267 +-----------+------------------------------------------------+-------+
268 | ``%p`` | Locale's equivalent of either AM or PM. | \(1) |
269 | | | |
270 +-----------+------------------------------------------------+-------+
271 | ``%S`` | Second as a decimal number [00,61]. | \(2) |
272 | | | |
273 +-----------+------------------------------------------------+-------+
274 | ``%U`` | Week number of the year (Sunday as the first | \(3) |
275 | | day of the week) as a decimal number [00,53]. | |
276 | | All days in a new year preceding the first | |
277 | | Sunday are considered to be in week 0. | |
278 | | | |
279 | | | |
280 | | | |
281 +-----------+------------------------------------------------+-------+
282 | ``%w`` | Weekday as a decimal number [0(Sunday),6]. | |
283 | | | |
284 +-----------+------------------------------------------------+-------+
285 | ``%W`` | Week number of the year (Monday as the first | \(3) |
286 | | day of the week) as a decimal number [00,53]. | |
287 | | All days in a new year preceding the first | |
288 | | Monday are considered to be in week 0. | |
289 | | | |
290 | | | |
291 | | | |
292 +-----------+------------------------------------------------+-------+
293 | ``%x`` | Locale's appropriate date representation. | |
294 | | | |
295 +-----------+------------------------------------------------+-------+
296 | ``%X`` | Locale's appropriate time representation. | |
297 | | | |
298 +-----------+------------------------------------------------+-------+
299 | ``%y`` | Year without century as a decimal number | |
300 | | [00,99]. | |
301 +-----------+------------------------------------------------+-------+
302 | ``%Y`` | Year with century as a decimal number. | |
303 | | | |
304 +-----------+------------------------------------------------+-------+
305 | ``%Z`` | Time zone name (no characters if no time zone | |
306 | | exists). | |
307 +-----------+------------------------------------------------+-------+
308 | ``%%`` | A literal ``'%'`` character. | |
309 +-----------+------------------------------------------------+-------+
Georg Brandl116aa622007-08-15 14:28:22 +0000310
311 Notes:
312
313 (1)
314 When used with the :func:`strptime` function, the ``%p`` directive only affects
315 the output hour field if the ``%I`` directive is used to parse the hour.
316
317 (2)
318 The range really is ``0`` to ``61``; this accounts for leap seconds and the
319 (very rare) double leap seconds.
320
321 (3)
322 When used with the :func:`strptime` function, ``%U`` and ``%W`` are only used in
323 calculations when the day of the week and the year are specified.
324
325 Here is an example, a format for dates compatible with that specified in the
326 :rfc:`2822` Internet email standard. [#]_ ::
327
328 >>> from time import gmtime, strftime
329 >>> strftime("%a, %d %b %Y %H:%M:%S +0000", gmtime())
330 'Thu, 28 Jun 2001 14:17:15 +0000'
331
332 Additional directives may be supported on certain platforms, but only the ones
333 listed here have a meaning standardized by ANSI C.
334
335 On some platforms, an optional field width and precision specification can
336 immediately follow the initial ``'%'`` of a directive in the following order;
337 this is also not portable. The field width is normally 2 except for ``%j`` where
338 it is 3.
339
340
341.. function:: strptime(string[, format])
342
343 Parse a string representing a time according to a format. The return value is
344 a :class:`struct_time` as returned by :func:`gmtime` or :func:`localtime`.
345
346 The *format* parameter uses the same directives as those used by
347 :func:`strftime`; it defaults to ``"%a %b %d %H:%M:%S %Y"`` which matches the
348 formatting returned by :func:`ctime`. If *string* cannot be parsed according to
349 *format*, or if it has excess data after parsing, :exc:`ValueError` is raised.
350 The default values used to fill in any missing data when more accurate values
351 cannot be inferred are ``(1900, 1, 1, 0, 0, 0, 0, 1, -1)``.
352
353 For example::
354
355 >>> import time
356 >>> time.strptime("30 Nov 00", "%d %b %y")
357 (2000, 11, 30, 0, 0, 0, 3, 335, -1)
358
359 Support for the ``%Z`` directive is based on the values contained in ``tzname``
360 and whether ``daylight`` is true. Because of this, it is platform-specific
361 except for recognizing UTC and GMT which are always known (and are considered to
362 be non-daylight savings timezones).
363
364 Only the directives specified in the documentation are supported. Because
365 ``strftime()`` is implemented per platform it can sometimes offer more
366 directives than those listed. But ``strptime()`` is independent of any platform
367 and thus does not necessarily support all directives available that are not
368 documented as supported.
369
370
371.. data:: struct_time
372
373 The type of the time value sequence returned by :func:`gmtime`,
374 :func:`localtime`, and :func:`strptime`.
375
Georg Brandl116aa622007-08-15 14:28:22 +0000376
377.. function:: time()
378
379 Return the time as a floating point number expressed in seconds since the epoch,
380 in UTC. Note that even though the time is always returned as a floating point
381 number, not all systems provide time with a better precision than 1 second.
382 While this function normally returns non-decreasing values, it can return a
383 lower value than a previous call if the system clock has been set back between
384 the two calls.
385
386
387.. data:: timezone
388
389 The offset of the local (non-DST) timezone, in seconds west of UTC (negative in
390 most of Western Europe, positive in the US, zero in the UK).
391
392
393.. data:: tzname
394
395 A tuple of two strings: the first is the name of the local non-DST timezone, the
396 second is the name of the local DST timezone. If no DST timezone is defined,
397 the second string should not be used.
398
399
400.. function:: tzset()
401
402 Resets the time conversion rules used by the library routines. The environment
403 variable :envvar:`TZ` specifies how this is done.
404
Georg Brandl116aa622007-08-15 14:28:22 +0000405 Availability: Unix.
406
407 .. note::
408
409 Although in many cases, changing the :envvar:`TZ` environment variable may
410 affect the output of functions like :func:`localtime` without calling
411 :func:`tzset`, this behavior should not be relied on.
412
413 The :envvar:`TZ` environment variable should contain no whitespace.
414
415 The standard format of the :envvar:`TZ` environment variable is (whitespace
416 added for clarity)::
417
418 std offset [dst [offset [,start[/time], end[/time]]]]
419
420 Where the components are:
421
422 ``std`` and ``dst``
423 Three or more alphanumerics giving the timezone abbreviations. These will be
424 propagated into time.tzname
425
426 ``offset``
427 The offset has the form: ``± hh[:mm[:ss]]``. This indicates the value
428 added the local time to arrive at UTC. If preceded by a '-', the timezone
429 is east of the Prime Meridian; otherwise, it is west. If no offset follows
430 dst, summer time is assumed to be one hour ahead of standard time.
431
432 ``start[/time], end[/time]``
433 Indicates when to change to and back from DST. The format of the
434 start and end dates are one of the following:
435
436 :samp:`J{n}`
437 The Julian day *n* (1 <= *n* <= 365). Leap days are not counted, so in
438 all years February 28 is day 59 and March 1 is day 60.
439
440 :samp:`{n}`
441 The zero-based Julian day (0 <= *n* <= 365). Leap days are counted, and
442 it is possible to refer to February 29.
443
444 :samp:`M{m}.{n}.{d}`
445 The *d*'th day (0 <= *d* <= 6) or week *n* of month *m* of the year (1
446 <= *n* <= 5, 1 <= *m* <= 12, where week 5 means "the last *d* day in
447 month *m*" which may occur in either the fourth or the fifth
448 week). Week 1 is the first week in which the *d*'th day occurs. Day
449 zero is Sunday.
450
451 ``time`` has the same format as ``offset`` except that no leading sign
452 ('-' or '+') is allowed. The default, if time is not given, is 02:00:00.
453
454 ::
455
456 >>> os.environ['TZ'] = 'EST+05EDT,M4.1.0,M10.5.0'
457 >>> time.tzset()
458 >>> time.strftime('%X %x %Z')
459 '02:07:36 05/08/03 EDT'
460 >>> os.environ['TZ'] = 'AEST-10AEDT-11,M10.5.0,M3.5.0'
461 >>> time.tzset()
462 >>> time.strftime('%X %x %Z')
463 '16:08:12 05/08/03 AEST'
464
465 On many Unix systems (including \*BSD, Linux, Solaris, and Darwin), it is more
466 convenient to use the system's zoneinfo (:manpage:`tzfile(5)`) database to
467 specify the timezone rules. To do this, set the :envvar:`TZ` environment
468 variable to the path of the required timezone datafile, relative to the root of
469 the systems 'zoneinfo' timezone database, usually located at
470 :file:`/usr/share/zoneinfo`. For example, ``'US/Eastern'``,
471 ``'Australia/Melbourne'``, ``'Egypt'`` or ``'Europe/Amsterdam'``. ::
472
473 >>> os.environ['TZ'] = 'US/Eastern'
474 >>> time.tzset()
475 >>> time.tzname
476 ('EST', 'EDT')
477 >>> os.environ['TZ'] = 'Egypt'
478 >>> time.tzset()
479 >>> time.tzname
480 ('EET', 'EEST')
481
482
483.. seealso::
484
485 Module :mod:`datetime`
486 More object-oriented interface to dates and times.
487
488 Module :mod:`locale`
489 Internationalization services. The locale settings can affect the return values
490 for some of the functions in the :mod:`time` module.
491
492 Module :mod:`calendar`
493 General calendar-related functions. :func:`timegm` is the inverse of
494 :func:`gmtime` from this module.
495
496.. rubric:: Footnotes
497
498.. [#] The use of ``%Z`` is now deprecated, but the ``%z`` escape that expands to the
499 preferred hour/minute offset is not supported by all ANSI C libraries. Also, a
500 strict reading of the original 1982 :rfc:`822` standard calls for a two-digit
501 year (%y rather than %Y), but practice moved to 4-digit years long before the
502 year 2000. The 4-digit year has been mandated by :rfc:`2822`, which obsoletes
503 :rfc:`822`.
504