1
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.. _time-y2kissues:
37
38* **Year 2000 (Y2K) issues**:  Python depends on the platform's C library, which
39  generally doesn't have year 2000 issues, since all dates and times are
40  represented internally as seconds since the epoch.  Functions accepting a
41  :class:`struct_time` (see below) generally require a 4-digit year.  For backward
42  compatibility, 2-digit years are supported if the module variable
43  ``accept2dyear`` is a non-zero integer; this variable is initialized to ``1``
44  unless the environment variable :envvar:`PYTHONY2K` is set to a non-empty
45  string, in which case it is initialized to ``0``.  Thus, you can set
46  :envvar:`PYTHONY2K` to a non-empty string in the environment to require 4-digit
47  years for all year input.  When 2-digit years are accepted, they are converted
48  according to the POSIX or X/Open standard: values 69-99 are mapped to 1969-1999,
49  and values 0--68 are mapped to 2000--2068. Values 100--1899 are always illegal.
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.
71
72* On the other hand, the precision of :func:`.time` and :func:`sleep` is better
73  than their Unix equivalents: times are expressed as floating point numbers,
74  :func:`.time` returns the most accurate time available (using Unix
75  :c:func:`gettimeofday` where available), and :func:`sleep` will accept a time
76  with a nonzero fraction (Unix :c:func:`select` is used to implement this, where
77  available).
78
79* The time value as returned by :func:`gmtime`, :func:`localtime`, and
80  :func:`strptime`, and accepted by :func:`asctime`, :func:`mktime` and
81  :func:`strftime`, may be considered as a sequence of 9 integers.  The return
82  values of :func:`gmtime`, :func:`localtime`, and :func:`strptime` also offer
83  attribute names for individual fields.
84
85  See :class:`struct_time` for a description of these objects.
86
87  .. versionchanged:: 2.2
88     The time value sequence was changed from a tuple to a :class:`struct_time`, with
89     the addition of attribute names for the fields.
90
91* Use the following functions to convert between time representations:
92
93  +-------------------------+-------------------------+-------------------------+
94  | From                    | To                      | Use                     |
95  +=========================+=========================+=========================+
96  | seconds since the epoch | :class:`struct_time` in | :func:`gmtime`          |
97  |                         | UTC                     |                         |
98  +-------------------------+-------------------------+-------------------------+
99  | seconds since the epoch | :class:`struct_time` in | :func:`localtime`       |
100  |                         | local time              |                         |
101  +-------------------------+-------------------------+-------------------------+
102  | :class:`struct_time` in | seconds since the epoch | :func:`calendar.timegm` |
103  | UTC                     |                         |                         |
104  +-------------------------+-------------------------+-------------------------+
105  | :class:`struct_time` in | seconds since the epoch | :func:`mktime`          |
106  | local time              |                         |                         |
107  +-------------------------+-------------------------+-------------------------+
108
109
110The module defines the following functions and data items:
111
112.. data:: accept2dyear
113
114   Boolean value indicating whether two-digit year values will be accepted.  This
115   is true by default, but will be set to false if the environment variable
116   :envvar:`PYTHONY2K` has been set to a non-empty string.  It may also be modified
117   at run time.
118
119
120.. data:: altzone
121
122   The offset of the local DST timezone, in seconds west of UTC, if one is defined.
123   This is negative if the local DST timezone is east of UTC (as in Western Europe,
124   including the UK).  Only use this if ``daylight`` is nonzero.
125
126
127.. function:: asctime([t])
128
129   Convert a tuple or :class:`struct_time` representing a time as returned by
130   :func:`gmtime` or :func:`localtime` to a 24-character string of the following
131   form: ``'Sun Jun 20 23:21:05 1993'``.  If *t* is not provided, the current time
132   as returned by :func:`localtime` is used. Locale information is not used by
133   :func:`asctime`.
134
135   .. note::
136
137      Unlike the C function of the same name, there is no trailing newline.
138
139   .. versionchanged:: 2.1
140      Allowed *t* to be omitted.
141
142
143.. function:: clock()
144
145   .. index::
146      single: CPU time
147      single: processor time
148      single: benchmarking
149
150   On Unix, return the current processor time as a floating point number expressed
151   in seconds.  The precision, and in fact the very definition of the meaning of
152   "processor time", depends on that of the C function of the same name, but in any
153   case, this is the function to use for benchmarking Python or timing algorithms.
154
155   On Windows, this function returns wall-clock seconds elapsed since the first
156   call to this function, as a floating point number, based on the Win32 function
157   :c:func:`QueryPerformanceCounter`. The resolution is typically better than one
158   microsecond.
159
160
161.. function:: ctime([secs])
162
163   Convert a time expressed in seconds since the epoch to a string representing
164   local time. If *secs* is not provided or :const:`None`, the current time as
165   returned by :func:`.time` is used.  ``ctime(secs)`` is equivalent to
166   ``asctime(localtime(secs))``. Locale information is not used by :func:`ctime`.
167
168   .. versionchanged:: 2.1
169      Allowed *secs* to be omitted.
170
171   .. versionchanged:: 2.4
172      If *secs* is :const:`None`, the current time is used.
173
174
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
189   .. versionchanged:: 2.1
190      Allowed *secs* to be omitted.
191
192   .. versionchanged:: 2.4
193      If *secs* is :const:`None`, the current time is used.
194
195
196.. function:: localtime([secs])
197
198   Like :func:`gmtime` but converts to local time.  If *secs* is not provided or
199   :const:`None`, the current time as returned by :func:`.time` is used.  The dst
200   flag is set to ``1`` when DST applies to the given time.
201
202   .. versionchanged:: 2.1
203      Allowed *secs* to be omitted.
204
205   .. versionchanged:: 2.4
206      If *secs* is :const:`None`, the current time is used.
207
208
209.. function:: mktime(t)
210
211   This is the inverse function of :func:`localtime`.  Its argument is the
212   :class:`struct_time` or full 9-tuple (since the dst flag is needed; use ``-1``
213   as the dst flag if it is unknown) which expresses the time in *local* time, not
214   UTC.  It returns a floating point number, for compatibility with :func:`.time`.
215   If the input value cannot be represented as a valid time, either
216   :exc:`OverflowError` or :exc:`ValueError` will be raised (which depends on
217   whether the invalid value is caught by Python or the underlying C libraries).
218   The earliest date for which it can generate a time is platform-dependent.
219
220
221.. function:: sleep(secs)
222
223   Suspend execution of the current thread for the given number of seconds.
224   The argument may be a floating point number to indicate a more precise sleep
225   time. The actual suspension time may be less than that requested because any
226   caught signal will terminate the :func:`sleep` following execution of that
227   signal's catching routine.  Also, the suspension time may be longer than
228   requested by an arbitrary amount because of the scheduling of other activity
229   in the system.
230
231
232.. function:: strftime(format[, t])
233
234   Convert a tuple or :class:`struct_time` representing a time as returned by
235   :func:`gmtime` or :func:`localtime` to a string as specified by the *format*
236   argument.  If *t* is not provided, the current time as returned by
237   :func:`localtime` is used.  *format* must be a string.  :exc:`ValueError` is
238   raised if any field in *t* is outside of the allowed range. :func:`strftime`
239   returns a locale dependent byte string; the result may be converted to unicode
240   by doing ``strftime(<myformat>).decode(locale.getlocale()[1])``.
241
242   .. versionchanged:: 2.1
243      Allowed *t* to be omitted.
244
245   .. versionchanged:: 2.4
246      :exc:`ValueError` raised if a field in *t* is out of range.
247
248   .. versionchanged:: 2.5
249      0 is now a legal argument for any position in the time tuple; if it is normally
250      illegal the value is forced to a correct one.
251
252   The following directives can be embedded in the *format* string. They are shown
253   without the optional field width and precision specification, and are replaced
254   by the indicated characters in the :func:`strftime` result:
255
256   +-----------+--------------------------------+-------+
257   | Directive | Meaning                        | Notes |
258   +===========+================================+=======+
259   | ``%a``    | Locale's abbreviated weekday   |       |
260   |           | name.                          |       |
261   +-----------+--------------------------------+-------+
262   | ``%A``    | Locale's full weekday name.    |       |
263   +-----------+--------------------------------+-------+
264   | ``%b``    | Locale's abbreviated month     |       |
265   |           | name.                          |       |
266   +-----------+--------------------------------+-------+
267   | ``%B``    | Locale's full month name.      |       |
268   +-----------+--------------------------------+-------+
269   | ``%c``    | Locale's appropriate date and  |       |
270   |           | time representation.           |       |
271   +-----------+--------------------------------+-------+
272   | ``%d``    | Day of the month as a decimal  |       |
273   |           | number [01,31].                |       |
274   +-----------+--------------------------------+-------+
275   | ``%H``    | Hour (24-hour clock) as a      |       |
276   |           | decimal number [00,23].        |       |
277   +-----------+--------------------------------+-------+
278   | ``%I``    | Hour (12-hour clock) as a      |       |
279   |           | decimal number [01,12].        |       |
280   +-----------+--------------------------------+-------+
281   | ``%j``    | Day of the year as a decimal   |       |
282   |           | number [001,366].              |       |
283   +-----------+--------------------------------+-------+
284   | ``%m``    | Month as a decimal number      |       |
285   |           | [01,12].                       |       |
286   +-----------+--------------------------------+-------+
287   | ``%M``    | Minute as a decimal number     |       |
288   |           | [00,59].                       |       |
289   +-----------+--------------------------------+-------+
290   | ``%p``    | Locale's equivalent of either  | \(1)  |
291   |           | AM or PM.                      |       |
292   +-----------+--------------------------------+-------+
293   | ``%S``    | Second as a decimal number     | \(2)  |
294   |           | [00,61].                       |       |
295   +-----------+--------------------------------+-------+
296   | ``%U``    | Week number of the year        | \(3)  |
297   |           | (Sunday as the first day of    |       |
298   |           | the week) as a decimal number  |       |
299   |           | [00,53].  All days in a new    |       |
300   |           | year preceding the first       |       |
301   |           | Sunday are considered to be in |       |
302   |           | week 0.                        |       |
303   +-----------+--------------------------------+-------+
304   | ``%w``    | Weekday as a decimal number    |       |
305   |           | [0(Sunday),6].                 |       |
306   +-----------+--------------------------------+-------+
307   | ``%W``    | Week number of the year        | \(3)  |
308   |           | (Monday as the first day of    |       |
309   |           | the week) as a decimal number  |       |
310   |           | [00,53].  All days in a new    |       |
311   |           | year preceding the first       |       |
312   |           | Monday are considered to be in |       |
313   |           | week 0.                        |       |
314   +-----------+--------------------------------+-------+
315   | ``%x``    | Locale's appropriate date      |       |
316   |           | representation.                |       |
317   +-----------+--------------------------------+-------+
318   | ``%X``    | Locale's appropriate time      |       |
319   |           | representation.                |       |
320   +-----------+--------------------------------+-------+
321   | ``%y``    | Year without century as a      |       |
322   |           | decimal number [00,99].        |       |
323   +-----------+--------------------------------+-------+
324   | ``%Y``    | Year with century as a decimal |       |
325   |           | number.                        |       |
326   +-----------+--------------------------------+-------+
327   | ``%Z``    | Time zone name (no characters  |       |
328   |           | if no time zone exists).       |       |
329   +-----------+--------------------------------+-------+
330   | ``%%``    | A literal ``'%'`` character.   |       |
331   +-----------+--------------------------------+-------+
332
333   Notes:
334
335   (1)
336      When used with the :func:`strptime` function, the ``%p`` directive only affects
337      the output hour field if the ``%I`` directive is used to parse the hour.
338
339   (2)
340      The range really is ``0`` to ``61``; this accounts for leap seconds and the
341      (very rare) double leap seconds.
342
343   (3)
344      When used with the :func:`strptime` function, ``%U`` and ``%W`` are only used in
345      calculations when the day of the week and the year are specified.
346
347   Here is an example, a format for dates compatible with that specified  in the
348   :rfc:`2822` Internet email standard.  [#]_ ::
349
350      >>> from time import gmtime, strftime
351      >>> strftime("%a, %d %b %Y %H:%M:%S +0000", gmtime())
352      'Thu, 28 Jun 2001 14:17:15 +0000'
353
354   Additional directives may be supported on certain platforms, but only the
355   ones listed here have a meaning standardized by ANSI C.  To see the full set
356   of format codes supported on your platform, consult the :manpage:`strftime(3)`
357   documentation.
358
359   On some platforms, an optional field width and precision specification can
360   immediately follow the initial ``'%'`` of a directive in the following order;
361   this is also not portable. The field width is normally 2 except for ``%j`` where
362   it is 3.
363
364
365.. function:: strptime(string[, format])
366
367   Parse a string representing a time according to a format.  The return  value is
368   a :class:`struct_time` as returned by :func:`gmtime` or :func:`localtime`.
369
370   The *format* parameter uses the same directives as those used by
371   :func:`strftime`; it defaults to ``"%a %b %d %H:%M:%S %Y"`` which matches the
372   formatting returned by :func:`ctime`. If *string* cannot be parsed according to
373   *format*, or if it has excess data after parsing, :exc:`ValueError` is raised.
374   The default values used to fill in any missing data when more accurate values
375   cannot be inferred are ``(1900, 1, 1, 0, 0, 0, 0, 1, -1)``.
376
377   For example:
378
379      >>> import time
380      >>> time.strptime("30 Nov 00", "%d %b %y")   # doctest: +NORMALIZE_WHITESPACE
381      time.struct_time(tm_year=2000, tm_mon=11, tm_mday=30, tm_hour=0, tm_min=0,
382                       tm_sec=0, tm_wday=3, tm_yday=335, tm_isdst=-1)
383
384   Support for the ``%Z`` directive is based on the values contained in ``tzname``
385   and whether ``daylight`` is true.  Because of this, it is platform-specific
386   except for recognizing UTC and GMT which are always known (and are considered to
387   be non-daylight savings timezones).
388
389   Only the directives specified in the documentation are supported.  Because
390   ``strftime()`` is implemented per platform it can sometimes offer more
391   directives than those listed.  But ``strptime()`` is independent of any platform
392   and thus does not necessarily support all directives available that are not
393   documented as supported.
394
395
396.. class:: struct_time
397
398   The type of the time value sequence returned by :func:`gmtime`,
399   :func:`localtime`, and :func:`strptime`.  It is an object with a :term:`named
400   tuple` interface: values can be accessed by index and by attribute name.  The
401   following values are present:
402
403   +-------+-------------------+---------------------------------+
404   | Index | Attribute         | Values                          |
405   +=======+===================+=================================+
406   | 0     | :attr:`tm_year`   | (for example, 1993)             |
407   +-------+-------------------+---------------------------------+
408   | 1     | :attr:`tm_mon`    | range [1, 12]                   |
409   +-------+-------------------+---------------------------------+
410   | 2     | :attr:`tm_mday`   | range [1, 31]                   |
411   +-------+-------------------+---------------------------------+
412   | 3     | :attr:`tm_hour`   | range [0, 23]                   |
413   +-------+-------------------+---------------------------------+
414   | 4     | :attr:`tm_min`    | range [0, 59]                   |
415   +-------+-------------------+---------------------------------+
416   | 5     | :attr:`tm_sec`    | range [0, 61]; see **(2)** in   |
417   |       |                   | :func:`strftime` description    |
418   +-------+-------------------+---------------------------------+
419   | 6     | :attr:`tm_wday`   | range [0, 6], Monday is 0       |
420   +-------+-------------------+---------------------------------+
421   | 7     | :attr:`tm_yday`   | range [1, 366]                  |
422   +-------+-------------------+---------------------------------+
423   | 8     | :attr:`tm_isdst`  | 0, 1 or -1; see below           |
424   +-------+-------------------+---------------------------------+
425
426   .. versionadded:: 2.2
427
428   Note that unlike the C structure, the month value is a range of [1, 12], not
429   [0, 11].  A year value will be handled as described under :ref:`Year 2000
430   (Y2K) issues <time-y2kissues>` above.
431
432   In calls to :func:`mktime`, :attr:`tm_isdst` may be set to 1 when daylight
433   savings time is in effect, and 0 when it is not.  A value of -1 indicates
434   that this is not known, and will usually result in the correct state being
435   filled in.
436
437   When a tuple with an incorrect length is passed to a function expecting a
438   :class:`struct_time`, or having elements of the wrong type, a
439   :exc:`TypeError` is raised.
440
441
442.. function:: time()
443
444   Return the time in seconds since the epoch as a floating point number.
445   Note that even though the time is always returned as a floating point
446   number, not all systems provide time with a better precision than 1 second.
447   While this function normally returns non-decreasing values, it can return a
448   lower value than a previous call if the system clock has been set back between
449   the two calls.
450
451
452.. data:: timezone
453
454   The offset of the local (non-DST) timezone, in seconds west of UTC (negative in
455   most of Western Europe, positive in the US, zero in the UK).
456
457
458.. data:: tzname
459
460   A tuple of two strings: the first is the name of the local non-DST timezone, the
461   second is the name of the local DST timezone.  If no DST timezone is defined,
462   the second string should not be used.
463
464
465.. function:: tzset()
466
467   Reset the time conversion rules used by the library routines. The environment
468   variable :envvar:`TZ` specifies how this is done. It will also set the variables
469   ``tzname`` (from the :envvar:`TZ` environment variable), ``timezone`` (non-DST
470   seconds West of UTC), ``altzone`` (DST seconds west of UTC) and ``daylight``
471   (to 0 if this timezone does not have any daylight saving time rules, or to
472   nonzero if there is a time, past, present or future when daylight saving time
473   applies).
474
475   .. versionadded:: 2.3
476
477   Availability: Unix.
478
479   .. note::
480
481      Although in many cases, changing the :envvar:`TZ` environment variable may
482      affect the output of functions like :func:`localtime` without calling
483      :func:`tzset`, this behavior should not be relied on.
484
485      The :envvar:`TZ` environment variable should contain no whitespace.
486
487   The standard format of the :envvar:`TZ` environment variable is (whitespace
488   added for clarity)::
489
490      std offset [dst [offset [,start[/time], end[/time]]]]
491
492   Where the components are:
493
494   ``std`` and ``dst``
495      Three or more alphanumerics giving the timezone abbreviations. These will be
496      propagated into time.tzname
497
498   ``offset``
499      The offset has the form: ``± hh[:mm[:ss]]``. This indicates the value
500      added the local time to arrive at UTC.  If preceded by a '-', the timezone
501      is east of the Prime Meridian; otherwise, it is west. If no offset follows
502      dst, summer time is assumed to be one hour ahead of standard time.
503
504   ``start[/time], end[/time]``
505      Indicates when to change to and back from DST. The format of the
506      start and end dates are one of the following:
507
508      :samp:`J{n}`
509         The Julian day *n* (1 <= *n* <= 365). Leap days are not counted, so in
510         all years February 28 is day 59 and March 1 is day 60.
511
512      :samp:`{n}`
513         The zero-based Julian day (0 <= *n* <= 365). Leap days are counted, and
514         it is possible to refer to February 29.
515
516      :samp:`M{m}.{n}.{d}`
517         The *d*'th day (0 <= *d* <= 6) or week *n* of month *m* of the year (1
518         <= *n* <= 5, 1 <= *m* <= 12, where week 5 means "the last *d* day in
519         month *m*" which may occur in either the fourth or the fifth
520         week). Week 1 is the first week in which the *d*'th day occurs. Day
521         zero is Sunday.
522
523      ``time`` has the same format as ``offset`` except that no leading sign
524      ('-' or '+') is allowed. The default, if time is not given, is 02:00:00.
525
526   ::
527
528      >>> os.environ['TZ'] = 'EST+05EDT,M4.1.0,M10.5.0'
529      >>> time.tzset()
530      >>> time.strftime('%X %x %Z')
531      '02:07:36 05/08/03 EDT'
532      >>> os.environ['TZ'] = 'AEST-10AEDT-11,M10.5.0,M3.5.0'
533      >>> time.tzset()
534      >>> time.strftime('%X %x %Z')
535      '16:08:12 05/08/03 AEST'
536
537   On many Unix systems (including \*BSD, Linux, Solaris, and Darwin), it is more
538   convenient to use the system's zoneinfo (:manpage:`tzfile(5)`)  database to
539   specify the timezone rules. To do this, set the  :envvar:`TZ` environment
540   variable to the path of the required timezone  datafile, relative to the root of
541   the systems 'zoneinfo' timezone database, usually located at
542   :file:`/usr/share/zoneinfo`. For example,  ``'US/Eastern'``,
543   ``'Australia/Melbourne'``, ``'Egypt'`` or  ``'Europe/Amsterdam'``. ::
544
545      >>> os.environ['TZ'] = 'US/Eastern'
546      >>> time.tzset()
547      >>> time.tzname
548      ('EST', 'EDT')
549      >>> os.environ['TZ'] = 'Egypt'
550      >>> time.tzset()
551      >>> time.tzname
552      ('EET', 'EEST')
553
554
555.. seealso::
556
557   Module :mod:`datetime`
558      More object-oriented interface to dates and times.
559
560   Module :mod:`locale`
561      Internationalization services.  The locale setting affects the interpretation
562      of many format specifiers in :func:`strftime` and :func:`strptime`.
563
564   Module :mod:`calendar`
565      General calendar-related functions.   :func:`~calendar.timegm` is the
566      inverse of :func:`gmtime` from this module.
567
568.. rubric:: Footnotes
569
570.. [#] The use of ``%Z`` is now deprecated, but the ``%z`` escape that expands to the
571   preferred  hour/minute offset is not supported by all ANSI C libraries. Also, a
572   strict reading of the original 1982 :rfc:`822` standard calls for a two-digit
573   year (%y rather than %Y), but practice moved to 4-digit years long before the
574   year 2000.  After that, :rfc:`822` became obsolete and the 4-digit year has
575   been first recommended by :rfc:`1123` and then mandated by :rfc:`2822`.
576
577