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2 :mod:`time` --- Time access and conversions
3 ===========================================
5 .. module:: time
6 :synopsis: Time access and conversions.
9 This module provides various time-related functions. For related
10 functionality, see also the :mod:`datetime` and :mod:`calendar` modules.
12 Although this module is always available,
13 not all functions are available on all platforms. Most of the functions
14 defined in this module call platform C library functions with the same name. It
15 may sometimes be helpful to consult the platform documentation, because the
16 semantics of these functions varies among platforms.
18 An explanation of some terminology and conventions is in order.
20 .. index:: single: epoch
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)``.
26 .. index:: single: Year 2038
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.
32 .. index::
33 single: Year 2000
34 single: Y2K
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.
51 .. index::
52 single: UTC
53 single: Coordinated Universal Time
54 single: Greenwich Mean Time
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.
60 .. index:: single: Daylight Saving Time
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.
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.
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).
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`, may be considered as a sequence of 9 integers. The return
83 values of :func:`gmtime`, :func:`localtime`, and :func:`strptime` also offer
84 attribute names for individual fields.
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 +-------+-------------------+---------------------------------+
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.
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.
118 .. versionchanged:: 2.2
119 The time value sequence was changed from a tuple to a :class:`struct_time`, with
120 the addition of attribute names for the fields.
123 The module defines the following functions and data items:
125 .. data:: accept2dyear
127 Boolean value indicating whether two-digit year values will be accepted. This
128 is true by default, but will be set to false if the environment variable
129 :envvar:`PYTHONY2K` has been set to a non-empty string. It may also be modified
130 at run time.
133 .. data:: altzone
135 The offset of the local DST timezone, in seconds west of UTC, if one is defined.
136 This is negative if the local DST timezone is east of UTC (as in Western Europe,
137 including the UK). Only use this if ``daylight`` is nonzero.
140 .. function:: asctime([t])
142 Convert a tuple or :class:`struct_time` representing a time as returned by
143 :func:`gmtime` or :func:`localtime` to a 24-character string of the following
144 form: ``'Sun Jun 20 23:21:05 1993'``. If *t* is not provided, the current time
145 as returned by :func:`localtime` is used. Locale information is not used by
146 :func:`asctime`.
148 .. note::
150 Unlike the C function of the same name, there is no trailing newline.
152 .. versionchanged:: 2.1
153 Allowed *t* to be omitted.
156 .. function:: clock()
158 .. index::
159 single: CPU time
160 single: processor time
161 single: benchmarking
163 On Unix, return the current processor time as a floating point number expressed
164 in seconds. The precision, and in fact the very definition of the meaning of
165 "processor time", depends on that of the C function of the same name, but in any
166 case, this is the function to use for benchmarking Python or timing algorithms.
168 On Windows, this function returns wall-clock seconds elapsed since the first
169 call to this function, as a floating point number, based on the Win32 function
170 :cfunc:`QueryPerformanceCounter`. The resolution is typically better than one
171 microsecond.
174 .. function:: ctime([secs])
176 Convert a time expressed in seconds since the epoch to a string representing
177 local time. If *secs* is not provided or :const:`None`, the current time as
178 returned by :func:`time` is used. ``ctime(secs)`` is equivalent to
179 ``asctime(localtime(secs))``. Locale information is not used by :func:`ctime`.
181 .. versionchanged:: 2.1
182 Allowed *secs* to be omitted.
184 .. versionchanged:: 2.4
185 If *secs* is :const:`None`, the current time is used.
188 .. data:: daylight
190 Nonzero if a DST timezone is defined.
193 .. function:: gmtime([secs])
195 Convert a time expressed in seconds since the epoch to a :class:`struct_time` in
196 UTC in which the dst flag is always zero. If *secs* is not provided or
197 :const:`None`, the current time as returned by :func:`time` is used. Fractions
198 of a second are ignored. See above for a description of the
199 :class:`struct_time` object. See :func:`calendar.timegm` for the inverse of this
200 function.
202 .. versionchanged:: 2.1
203 Allowed *secs* to be omitted.
205 .. versionchanged:: 2.4
206 If *secs* is :const:`None`, the current time is used.
209 .. function:: localtime([secs])
211 Like :func:`gmtime` but converts to local time. If *secs* is not provided or
212 :const:`None`, the current time as returned by :func:`time` is used. The dst
213 flag is set to ``1`` when DST applies to the given time.
215 .. versionchanged:: 2.1
216 Allowed *secs* to be omitted.
218 .. versionchanged:: 2.4
219 If *secs* is :const:`None`, the current time is used.
222 .. function:: mktime(t)
224 This is the inverse function of :func:`localtime`. Its argument is the
225 :class:`struct_time` or full 9-tuple (since the dst flag is needed; use ``-1``
226 as the dst flag if it is unknown) which expresses the time in *local* time, not
227 UTC. It returns a floating point number, for compatibility with :func:`time`.
228 If the input value cannot be represented as a valid time, either
229 :exc:`OverflowError` or :exc:`ValueError` will be raised (which depends on
230 whether the invalid value is caught by Python or the underlying C libraries).
231 The earliest date for which it can generate a time is platform-dependent.
234 .. function:: sleep(secs)
236 Suspend execution for the given number of seconds. The argument may be a
237 floating point number to indicate a more precise sleep time. The actual
238 suspension time may be less than that requested because any caught signal will
239 terminate the :func:`sleep` following execution of that signal's catching
240 routine. Also, the suspension time may be longer than requested by an arbitrary
241 amount because of the scheduling of other activity in the system.
244 .. function:: strftime(format[, t])
246 Convert a tuple or :class:`struct_time` representing a time as returned by
247 :func:`gmtime` or :func:`localtime` to a string as specified by the *format*
248 argument. If *t* is not provided, the current time as returned by
249 :func:`localtime` is used. *format* must be a string. :exc:`ValueError` is
250 raised if any field in *t* is outside of the allowed range.
252 .. versionchanged:: 2.1
253 Allowed *t* to be omitted.
255 .. versionchanged:: 2.4
256 :exc:`ValueError` raised if a field in *t* is out of range.
258 .. versionchanged:: 2.5
259 0 is now a legal argument for any position in the time tuple; if it is normally
260 illegal the value is forced to a correct one..
262 The following directives can be embedded in the *format* string. They are shown
263 without the optional field width and precision specification, and are replaced
264 by the indicated characters in the :func:`strftime` result:
266 +-----------+--------------------------------+-------+
267 | Directive | Meaning | Notes |
268 +===========+================================+=======+
269 | ``%a`` | Locale's abbreviated weekday | |
270 | | name. | |
271 +-----------+--------------------------------+-------+
272 | ``%A`` | Locale's full weekday name. | |
273 +-----------+--------------------------------+-------+
274 | ``%b`` | Locale's abbreviated month | |
275 | | name. | |
276 +-----------+--------------------------------+-------+
277 | ``%B`` | Locale's full month name. | |
278 +-----------+--------------------------------+-------+
279 | ``%c`` | Locale's appropriate date and | |
280 | | time representation. | |
281 +-----------+--------------------------------+-------+
282 | ``%d`` | Day of the month as a decimal | |
283 | | number [01,31]. | |
284 +-----------+--------------------------------+-------+
285 | ``%H`` | Hour (24-hour clock) as a | |
286 | | decimal number [00,23]. | |
287 +-----------+--------------------------------+-------+
288 | ``%I`` | Hour (12-hour clock) as a | |
289 | | decimal number [01,12]. | |
290 +-----------+--------------------------------+-------+
291 | ``%j`` | Day of the year as a decimal | |
292 | | number [001,366]. | |
293 +-----------+--------------------------------+-------+
294 | ``%m`` | Month as a decimal number | |
295 | | [01,12]. | |
296 +-----------+--------------------------------+-------+
297 | ``%M`` | Minute as a decimal number | |
298 | | [00,59]. | |
299 +-----------+--------------------------------+-------+
300 | ``%p`` | Locale's equivalent of either | \(1) |
301 | | AM or PM. | |
302 +-----------+--------------------------------+-------+
303 | ``%S`` | Second as a decimal number | \(2) |
304 | | [00,61]. | |
305 +-----------+--------------------------------+-------+
306 | ``%U`` | Week number of the year | \(3) |
307 | | (Sunday as the first day of | |
308 | | the week) as a decimal number | |
309 | | [00,53]. All days in a new | |
310 | | year preceding the first | |
311 | | Sunday are considered to be in | |
312 | | week 0. | |
313 +-----------+--------------------------------+-------+
314 | ``%w`` | Weekday as a decimal number | |
315 | | [0(Sunday),6]. | |
316 +-----------+--------------------------------+-------+
317 | ``%W`` | Week number of the year | \(3) |
318 | | (Monday as the first day of | |
319 | | the week) as a decimal number | |
320 | | [00,53]. All days in a new | |
321 | | year preceding the first | |
322 | | Monday are considered to be in | |
323 | | week 0. | |
324 +-----------+--------------------------------+-------+
325 | ``%x`` | Locale's appropriate date | |
326 | | representation. | |
327 +-----------+--------------------------------+-------+
328 | ``%X`` | Locale's appropriate time | |
329 | | representation. | |
330 +-----------+--------------------------------+-------+
331 | ``%y`` | Year without century as a | |
332 | | decimal number [00,99]. | |
333 +-----------+--------------------------------+-------+
334 | ``%Y`` | Year with century as a decimal | |
335 | | number. | |
336 +-----------+--------------------------------+-------+
337 | ``%Z`` | Time zone name (no characters | |
338 | | if no time zone exists). | |
339 +-----------+--------------------------------+-------+
340 | ``%%`` | A literal ``'%'`` character. | |
341 +-----------+--------------------------------+-------+
343 Notes:
345 (1)
346 When used with the :func:`strptime` function, the ``%p`` directive only affects
347 the output hour field if the ``%I`` directive is used to parse the hour.
349 (2)
350 The range really is ``0`` to ``61``; this accounts for leap seconds and the
351 (very rare) double leap seconds.
353 (3)
354 When used with the :func:`strptime` function, ``%U`` and ``%W`` are only used in
355 calculations when the day of the week and the year are specified.
357 Here is an example, a format for dates compatible with that specified in the
358 :rfc:`2822` Internet email standard. [#]_ ::
360 >>> from time import gmtime, strftime
361 >>> strftime("%a, %d %b %Y %H:%M:%S +0000", gmtime())
362 'Thu, 28 Jun 2001 14:17:15 +0000'
364 Additional directives may be supported on certain platforms, but only the ones
365 listed here have a meaning standardized by ANSI C.
367 On some platforms, an optional field width and precision specification can
368 immediately follow the initial ``'%'`` of a directive in the following order;
369 this is also not portable. The field width is normally 2 except for ``%j`` where
370 it is 3.
373 .. function:: strptime(string[, format])
375 Parse a string representing a time according to a format. The return value is
376 a :class:`struct_time` as returned by :func:`gmtime` or :func:`localtime`.
378 The *format* parameter uses the same directives as those used by
379 :func:`strftime`; it defaults to ``"%a %b %d %H:%M:%S %Y"`` which matches the
380 formatting returned by :func:`ctime`. If *string* cannot be parsed according to
381 *format*, or if it has excess data after parsing, :exc:`ValueError` is raised.
382 The default values used to fill in any missing data when more accurate values
383 cannot be inferred are ``(1900, 1, 1, 0, 0, 0, 0, 1, -1)``.
385 For example:
387 >>> import time
388 >>> time.strptime("30 Nov 00", "%d %b %y") # doctest: +NORMALIZE_WHITESPACE
389 time.struct_time(tm_year=2000, tm_mon=11, tm_mday=30, tm_hour=0, tm_min=0,
390 tm_sec=0, tm_wday=3, tm_yday=335, tm_isdst=-1)
392 Support for the ``%Z`` directive is based on the values contained in ``tzname``
393 and whether ``daylight`` is true. Because of this, it is platform-specific
394 except for recognizing UTC and GMT which are always known (and are considered to
395 be non-daylight savings timezones).
397 Only the directives specified in the documentation are supported. Because
398 ``strftime()`` is implemented per platform it can sometimes offer more
399 directives than those listed. But ``strptime()`` is independent of any platform
400 and thus does not necessarily support all directives available that are not
401 documented as supported.
404 .. data:: struct_time
406 The type of the time value sequence returned by :func:`gmtime`,
407 :func:`localtime`, and :func:`strptime`.
409 .. versionadded:: 2.2
412 .. function:: time()
414 Return the time as a floating point number expressed in seconds since the epoch,
415 in UTC. Note that even though the time is always returned as a floating point
416 number, not all systems provide time with a better precision than 1 second.
417 While this function normally returns non-decreasing values, it can return a
418 lower value than a previous call if the system clock has been set back between
419 the two calls.
422 .. data:: timezone
424 The offset of the local (non-DST) timezone, in seconds west of UTC (negative in
425 most of Western Europe, positive in the US, zero in the UK).
428 .. data:: tzname
430 A tuple of two strings: the first is the name of the local non-DST timezone, the
431 second is the name of the local DST timezone. If no DST timezone is defined,
432 the second string should not be used.
435 .. function:: tzset()
437 Resets the time conversion rules used by the library routines. The environment
438 variable :envvar:`TZ` specifies how this is done.
440 .. versionadded:: 2.3
442 Availability: Unix.
444 .. note::
446 Although in many cases, changing the :envvar:`TZ` environment variable may
447 affect the output of functions like :func:`localtime` without calling
448 :func:`tzset`, this behavior should not be relied on.
450 The :envvar:`TZ` environment variable should contain no whitespace.
452 The standard format of the :envvar:`TZ` environment variable is (whitespace
453 added for clarity)::
455 std offset [dst [offset [,start[/time], end[/time]]]]
457 Where the components are:
459 ``std`` and ``dst``
460 Three or more alphanumerics giving the timezone abbreviations. These will be
461 propagated into time.tzname
463 ``offset``
464 The offset has the form: ``± hh[:mm[:ss]]``. This indicates the value
465 added the local time to arrive at UTC. If preceded by a '-', the timezone
466 is east of the Prime Meridian; otherwise, it is west. If no offset follows
467 dst, summer time is assumed to be one hour ahead of standard time.
469 ``start[/time], end[/time]``
470 Indicates when to change to and back from DST. The format of the
471 start and end dates are one of the following:
473 :samp:`J{n}`
474 The Julian day *n* (1 <= *n* <= 365). Leap days are not counted, so in
475 all years February 28 is day 59 and March 1 is day 60.
477 :samp:`{n}`
478 The zero-based Julian day (0 <= *n* <= 365). Leap days are counted, and
479 it is possible to refer to February 29.
481 :samp:`M{m}.{n}.{d}`
482 The *d*'th day (0 <= *d* <= 6) or week *n* of month *m* of the year (1
483 <= *n* <= 5, 1 <= *m* <= 12, where week 5 means "the last *d* day in
484 month *m*" which may occur in either the fourth or the fifth
485 week). Week 1 is the first week in which the *d*'th day occurs. Day
486 zero is Sunday.
488 ``time`` has the same format as ``offset`` except that no leading sign
489 ('-' or '+') is allowed. The default, if time is not given, is 02:00:00.
491 ::
493 >>> os.environ['TZ'] = 'EST+05EDT,M4.1.0,M10.5.0'
494 >>> time.tzset()
495 >>> time.strftime('%X %x %Z')
496 '02:07:36 05/08/03 EDT'
497 >>> os.environ['TZ'] = 'AEST-10AEDT-11,M10.5.0,M3.5.0'
498 >>> time.tzset()
499 >>> time.strftime('%X %x %Z')
500 '16:08:12 05/08/03 AEST'
502 On many Unix systems (including \*BSD, Linux, Solaris, and Darwin), it is more
503 convenient to use the system's zoneinfo (:manpage:`tzfile(5)`) database to
504 specify the timezone rules. To do this, set the :envvar:`TZ` environment
505 variable to the path of the required timezone datafile, relative to the root of
506 the systems 'zoneinfo' timezone database, usually located at
507 :file:`/usr/share/zoneinfo`. For example, ``'US/Eastern'``,
508 ``'Australia/Melbourne'``, ``'Egypt'`` or ``'Europe/Amsterdam'``. ::
510 >>> os.environ['TZ'] = 'US/Eastern'
511 >>> time.tzset()
512 >>> time.tzname
513 ('EST', 'EDT')
514 >>> os.environ['TZ'] = 'Egypt'
515 >>> time.tzset()
516 >>> time.tzname
517 ('EET', 'EEST')
520 .. seealso::
522 Module :mod:`datetime`
523 More object-oriented interface to dates and times.
525 Module :mod:`locale`
526 Internationalization services. The locale settings can affect the return values
527 for some of the functions in the :mod:`time` module.
529 Module :mod:`calendar`
530 General calendar-related functions. :func:`timegm` is the inverse of
531 :func:`gmtime` from this module.
533 .. rubric:: Footnotes
535 .. [#] The use of ``%Z`` is now deprecated, but the ``%z`` escape that expands to the
536 preferred hour/minute offset is not supported by all ANSI C libraries. Also, a
537 strict reading of the original 1982 :rfc:`822` standard calls for a two-digit
538 year (%y rather than %Y), but practice moved to 4-digit years long before the
539 year 2000. The 4-digit year has been mandated by :rfc:`2822`, which obsoletes
540 :rfc:`822`.