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  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* **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.
 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  :cfunc:`gettimeofday` where available), and :func:`sleep` will accept a time
 76  with a nonzero fraction (Unix :cfunc:`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  +-------+-------------------+---------------------------------+
 86  | Index | Attribute         | Values                          |
 87  +=======+===================+=================================+
 88  | 0     | :attr:`tm_year`   | (for example, 1993)             |
 89  +-------+-------------------+---------------------------------+
 90  | 1     | :attr:`tm_mon`    | range [1,12]                    |
 91  +-------+-------------------+---------------------------------+
 92  | 2     | :attr:`tm_mday`   | range [1,31]                    |
 93  +-------+-------------------+---------------------------------+
 94  | 3     | :attr:`tm_hour`   | range [0,23]                    |
 95  +-------+-------------------+---------------------------------+
 96  | 4     | :attr:`tm_min`    | range [0,59]                    |
 97  +-------+-------------------+---------------------------------+
 98  | 5     | :attr:`tm_sec`    | range [0,61]; see **(1)** in    |
 99  |       |                   | :func:`strftime` description    |
100  +-------+-------------------+---------------------------------+
101  | 6     | :attr:`tm_wday`   | range [0,6], Monday is 0        |
102  +-------+-------------------+---------------------------------+
103  | 7     | :attr:`tm_yday`   | range [1,366]                   |
104  +-------+-------------------+---------------------------------+
105  | 8     | :attr:`tm_isdst`  | 0, 1 or -1; see below           |
106  +-------+-------------------+---------------------------------+
107
108  Note that unlike the C structure, the month value is a range of 1-12, not 0-11.
109  A year value will be handled as described under "Year 2000 (Y2K) issues" above.
110  A ``-1`` argument as the daylight savings flag, passed to :func:`mktime` will
111  usually result in the correct daylight savings state to be filled in.
112
113  When a tuple with an incorrect length is passed to a function expecting a
114  :class:`struct_time`, or having elements of the wrong type, a :exc:`TypeError`
115  is raised.
116
117  .. versionchanged:: 2.2
118     The time value sequence was changed from a tuple to a :class:`struct_time`, with
119     the addition of attribute names for the fields.
120
121* Use the following functions to convert between time representations:
122
123  +-------------------------+-------------------------+-------------------------+
124  | From                    | To                      | Use                     |
125  +=========================+=========================+=========================+
126  | seconds since the epoch | :class:`struct_time` in | :func:`gmtime`          |
127  |                         | UTC                     |                         |
128  +-------------------------+-------------------------+-------------------------+
129  | seconds since the epoch | :class:`struct_time` in | :func:`localtime`       |
130  |                         | local time              |                         |
131  +-------------------------+-------------------------+-------------------------+
132  | :class:`struct_time` in | seconds since the epoch | :func:`calendar.timegm` |
133  | UTC                     |                         |                         |
134  +-------------------------+-------------------------+-------------------------+
135  | :class:`struct_time` in | seconds since the epoch | :func:`mktime`          |
136  | local time              |                         |                         |
137  +-------------------------+-------------------------+-------------------------+
138
139
140The module defines the following functions and data items:
141
142.. data:: accept2dyear
143
144   Boolean value indicating whether two-digit year values will be accepted.  This
145   is true by default, but will be set to false if the environment variable
146   :envvar:`PYTHONY2K` has been set to a non-empty string.  It may also be modified
147   at run time.
148
149
150.. data:: altzone
151
152   The offset of the local DST timezone, in seconds west of UTC, if one is defined.
153   This is negative if the local DST timezone is east of UTC (as in Western Europe,
154   including the UK).  Only use this if ``daylight`` is nonzero.
155
156
157.. function:: asctime([t])
158
159   Convert a tuple or :class:`struct_time` representing a time as returned by
160   :func:`gmtime` or :func:`localtime` to a 24-character string of the following
161   form: ``'Sun Jun 20 23:21:05 1993'``.  If *t* is not provided, the current time
162   as returned by :func:`localtime` is used. Locale information is not used by
163   :func:`asctime`.
164
165   .. note::
166
167      Unlike the C function of the same name, there is no trailing newline.
168
169   .. versionchanged:: 2.1
170      Allowed *t* to be omitted.
171
172
173.. function:: clock()
174
175   .. index::
176      single: CPU time
177      single: processor time
178      single: benchmarking
179
180   On Unix, return the current processor time as a floating point number expressed
181   in seconds.  The precision, and in fact the very definition of the meaning of
182   "processor time", depends on that of the C function of the same name, but in any
183   case, this is the function to use for benchmarking Python or timing algorithms.
184
185   On Windows, this function returns wall-clock seconds elapsed since the first
186   call to this function, as a floating point number, based on the Win32 function
187   :cfunc:`QueryPerformanceCounter`. The resolution is typically better than one
188   microsecond.
189
190
191.. function:: ctime([secs])
192
193   Convert a time expressed in seconds since the epoch to a string representing
194   local time. If *secs* is not provided or :const:`None`, the current time as
195   returned by :func:`time` is used.  ``ctime(secs)`` is equivalent to
196   ``asctime(localtime(secs))``. Locale information is not used by :func:`ctime`.
197
198   .. versionchanged:: 2.1
199      Allowed *secs* to be omitted.
200
201   .. versionchanged:: 2.4
202      If *secs* is :const:`None`, the current time is used.
203
204
205.. data:: daylight
206
207   Nonzero if a DST timezone is defined.
208
209
210.. function:: gmtime([secs])
211
212   Convert a time expressed in seconds since the epoch to a :class:`struct_time` in
213   UTC in which the dst flag is always zero.  If *secs* is not provided or
214   :const:`None`, the current time as returned by :func:`time` is used.  Fractions
215   of a second are ignored.  See above for a description of the
216   :class:`struct_time` object. See :func:`calendar.timegm` for the inverse of this
217   function.
218
219   .. versionchanged:: 2.1
220      Allowed *secs* to be omitted.
221
222   .. versionchanged:: 2.4
223      If *secs* is :const:`None`, the current time is used.
224
225
226.. function:: localtime([secs])
227
228   Like :func:`gmtime` but converts to local time.  If *secs* is not provided or
229   :const:`None`, the current time as returned by :func:`time` is used.  The dst
230   flag is set to ``1`` when DST applies to the given time.
231
232   .. versionchanged:: 2.1
233      Allowed *secs* to be omitted.
234
235   .. versionchanged:: 2.4
236      If *secs* is :const:`None`, the current time is used.
237
238
239.. function:: mktime(t)
240
241   This is the inverse function of :func:`localtime`.  Its argument is the
242   :class:`struct_time` or full 9-tuple (since the dst flag is needed; use ``-1``
243   as the dst flag if it is unknown) which expresses the time in *local* time, not
244   UTC.  It returns a floating point number, for compatibility with :func:`time`.
245   If the input value cannot be represented as a valid time, either
246   :exc:`OverflowError` or :exc:`ValueError` will be raised (which depends on
247   whether the invalid value is caught by Python or the underlying C libraries).
248   The earliest date for which it can generate a time is platform-dependent.
249
250
251.. function:: sleep(secs)
252
253   Suspend execution for the given number of seconds.  The argument may be a
254   floating point number to indicate a more precise sleep time. The actual
255   suspension time may be less than that requested because any caught signal will
256   terminate the :func:`sleep` following execution of that signal's catching
257   routine.  Also, the suspension time may be longer than requested by an arbitrary
258   amount because of the scheduling of other activity in the system.
259
260
261.. function:: strftime(format[, t])
262
263   Convert a tuple or :class:`struct_time` representing a time as returned by
264   :func:`gmtime` or :func:`localtime` to a string as specified by the *format*
265   argument.  If *t* is not provided, the current time as returned by
266   :func:`localtime` is used.  *format* must be a string.  :exc:`ValueError` is
267   raised if any field in *t* is outside of the allowed range.
268
269   .. versionchanged:: 2.1
270      Allowed *t* to be omitted.
271
272   .. versionchanged:: 2.4
273      :exc:`ValueError` raised if a field in *t* is out of range.
274
275   .. versionchanged:: 2.5
276      0 is now a legal argument for any position in the time tuple; if it is normally
277      illegal the value is forced to a correct one..
278
279   The following directives can be embedded in the *format* string. They are shown
280   without the optional field width and precision specification, and are replaced
281   by the indicated characters in the :func:`strftime` result:
282
283   +-----------+--------------------------------+-------+
284   | Directive | Meaning                        | Notes |
285   +===========+================================+=======+
286   | ``%a``    | Locale's abbreviated weekday   |       |
287   |           | name.                          |       |
288   +-----------+--------------------------------+-------+
289   | ``%A``    | Locale's full weekday name.    |       |
290   +-----------+--------------------------------+-------+
291   | ``%b``    | Locale's abbreviated month     |       |
292   |           | name.                          |       |
293   +-----------+--------------------------------+-------+
294   | ``%B``    | Locale's full month name.      |       |
295   +-----------+--------------------------------+-------+
296   | ``%c``    | Locale's appropriate date and  |       |
297   |           | time representation.           |       |
298   +-----------+--------------------------------+-------+
299   | ``%d``    | Day of the month as a decimal  |       |
300   |           | number [01,31].                |       |
301   +-----------+--------------------------------+-------+
302   | ``%H``    | Hour (24-hour clock) as a      |       |
303   |           | decimal number [00,23].        |       |
304   +-----------+--------------------------------+-------+
305   | ``%I``    | Hour (12-hour clock) as a      |       |
306   |           | decimal number [01,12].        |       |
307   +-----------+--------------------------------+-------+
308   | ``%j``    | Day of the year as a decimal   |       |
309   |           | number [001,366].              |       |
310   +-----------+--------------------------------+-------+
311   | ``%m``    | Month as a decimal number      |       |
312   |           | [01,12].                       |       |
313   +-----------+--------------------------------+-------+
314   | ``%M``    | Minute as a decimal number     |       |
315   |           | [00,59].                       |       |
316   +-----------+--------------------------------+-------+
317   | ``%p``    | Locale's equivalent of either  | \(1)  |
318   |           | AM or PM.                      |       |
319   +-----------+--------------------------------+-------+
320   | ``%S``    | Second as a decimal number     | \(2)  |
321   |           | [00,61].                       |       |
322   +-----------+--------------------------------+-------+
323   | ``%U``    | Week number of the year        | \(3)  |
324   |           | (Sunday as the first day of    |       |
325   |           | the week) as a decimal number  |       |
326   |           | [00,53].  All days in a new    |       |
327   |           | year preceding the first       |       |
328   |           | Sunday are considered to be in |       |
329   |           | week 0.                        |       |
330   +-----------+--------------------------------+-------+
331   | ``%w``    | Weekday as a decimal number    |       |
332   |           | [0(Sunday),6].                 |       |
333   +-----------+--------------------------------+-------+
334   | ``%W``    | Week number of the year        | \(3)  |
335   |           | (Monday as the first day of    |       |
336   |           | the week) as a decimal number  |       |
337   |           | [00,53].  All days in a new    |       |
338   |           | year preceding the first       |       |
339   |           | Monday are considered to be in |       |
340   |           | week 0.                        |       |
341   +-----------+--------------------------------+-------+
342   | ``%x``    | Locale's appropriate date      |       |
343   |           | representation.                |       |
344   +-----------+--------------------------------+-------+
345   | ``%X``    | Locale's appropriate time      |       |
346   |           | representation.                |       |
347   +-----------+--------------------------------+-------+
348   | ``%y``    | Year without century as a      |       |
349   |           | decimal number [00,99].        |       |
350   +-----------+--------------------------------+-------+
351   | ``%Y``    | Year with century as a decimal |       |
352   |           | number.                        |       |
353   +-----------+--------------------------------+-------+
354   | ``%Z``    | Time zone name (no characters  |       |
355   |           | if no time zone exists).       |       |
356   +-----------+--------------------------------+-------+
357   | ``%%``    | A literal ``'%'`` character.   |       |
358   +-----------+--------------------------------+-------+
359
360   Notes:
361
362   (1)
363      When used with the :func:`strptime` function, the ``%p`` directive only affects
364      the output hour field if the ``%I`` directive is used to parse the hour.
365
366   (2)
367      The range really is ``0`` to ``61``; this accounts for leap seconds and the
368      (very rare) double leap seconds.
369
370   (3)
371      When used with the :func:`strptime` function, ``%U`` and ``%W`` are only used in
372      calculations when the day of the week and the year are specified.
373
374   Here is an example, a format for dates compatible with that specified  in the
375   :rfc:`2822` Internet email standard.  [#]_ ::
376
377      >>> from time import gmtime, strftime
378      >>> strftime("%a, %d %b %Y %H:%M:%S +0000", gmtime())
379      'Thu, 28 Jun 2001 14:17:15 +0000'
380
381   Additional directives may be supported on certain platforms, but only the ones
382   listed here have a meaning standardized by ANSI C.
383
384   On some platforms, an optional field width and precision specification can
385   immediately follow the initial ``'%'`` of a directive in the following order;
386   this is also not portable. The field width is normally 2 except for ``%j`` where
387   it is 3.
388
389
390.. function:: strptime(string[, format])
391
392   Parse a string representing a time according to a format.  The return  value is
393   a :class:`struct_time` as returned by :func:`gmtime` or :func:`localtime`.
394
395   The *format* parameter uses the same directives as those used by
396   :func:`strftime`; it defaults to ``"%a %b %d %H:%M:%S %Y"`` which matches the
397   formatting returned by :func:`ctime`. If *string* cannot be parsed according to
398   *format*, or if it has excess data after parsing, :exc:`ValueError` is raised.
399   The default values used to fill in any missing data when more accurate values
400   cannot be inferred are ``(1900, 1, 1, 0, 0, 0, 0, 1, -1)``.
401
402   For example:
403
404      >>> import time
405      >>> time.strptime("30 Nov 00", "%d %b %y")   # doctest: +NORMALIZE_WHITESPACE
406      time.struct_time(tm_year=2000, tm_mon=11, tm_mday=30, tm_hour=0, tm_min=0,
407                       tm_sec=0, tm_wday=3, tm_yday=335, tm_isdst=-1)
408
409   Support for the ``%Z`` directive is based on the values contained in ``tzname``
410   and whether ``daylight`` is true.  Because of this, it is platform-specific
411   except for recognizing UTC and GMT which are always known (and are considered to
412   be non-daylight savings timezones).
413
414   Only the directives specified in the documentation are supported.  Because
415   ``strftime()`` is implemented per platform it can sometimes offer more
416   directives than those listed.  But ``strptime()`` is independent of any platform
417   and thus does not necessarily support all directives available that are not
418   documented as supported.
419
420
421.. data:: struct_time
422
423   The type of the time value sequence returned by :func:`gmtime`,
424   :func:`localtime`, and :func:`strptime`.
425
426   .. versionadded:: 2.2
427
428
429.. function:: time()
430
431   Return the time as a floating point number expressed in seconds since the epoch,
432   in UTC.  Note that even though the time is always returned as a floating point
433   number, not all systems provide time with a better precision than 1 second.
434   While this function normally returns non-decreasing values, it can return a
435   lower value than a previous call if the system clock has been set back between
436   the two calls.
437
438
439.. data:: timezone
440
441   The offset of the local (non-DST) timezone, in seconds west of UTC (negative in
442   most of Western Europe, positive in the US, zero in the UK).
443
444
445.. data:: tzname
446
447   A tuple of two strings: the first is the name of the local non-DST timezone, the
448   second is the name of the local DST timezone.  If no DST timezone is defined,
449   the second string should not be used.
450
451
452.. function:: tzset()
453
454   Resets the time conversion rules used by the library routines. The environment
455   variable :envvar:`TZ` specifies how this is done.
456
457   .. versionadded:: 2.3
458
459   Availability: Unix.
460
461   .. note::
462
463      Although in many cases, changing the :envvar:`TZ` environment variable may
464      affect the output of functions like :func:`localtime` without calling
465      :func:`tzset`, this behavior should not be relied on.
466
467      The :envvar:`TZ` environment variable should contain no whitespace.
468
469   The standard format of the :envvar:`TZ` environment variable is (whitespace
470   added for clarity)::
471
472      std offset [dst [offset [,start[/time], end[/time]]]]
473
474   Where the components are:
475
476   ``std`` and ``dst``
477      Three or more alphanumerics giving the timezone abbreviations. These will be
478      propagated into time.tzname
479
480   ``offset``
481      The offset has the form: ``Âą hh[:mm[:ss]]``. This indicates the value
482      added the local time to arrive at UTC.  If preceded by a '-', the timezone
483      is east of the Prime Meridian; otherwise, it is west. If no offset follows
484      dst, summer time is assumed to be one hour ahead of standard time.
485
486   ``start[/time], end[/time]``
487      Indicates when to change to and back from DST. The format of the
488      start and end dates are one of the following:
489
490      :samp:`J{n}`
491         The Julian day *n* (1 <= *n* <= 365). Leap days are not counted, so in
492         all years February 28 is day 59 and March 1 is day 60.
493
494      :samp:`{n}`
495         The zero-based Julian day (0 <= *n* <= 365). Leap days are counted, and
496         it is possible to refer to February 29.
497
498      :samp:`M{m}.{n}.{d}`
499         The *d*'th day (0 <= *d* <= 6) or week *n* of month *m* of the year (1
500         <= *n* <= 5, 1 <= *m* <= 12, where week 5 means "the last *d* day in
501         month *m*" which may occur in either the fourth or the fifth
502         week). Week 1 is the first week in which the *d*'th day occurs. Day
503         zero is Sunday.
504
505      ``time`` has the same format as ``offset`` except that no leading sign
506      ('-' or '+') is allowed. The default, if time is not given, is 02:00:00.
507
508   ::
509
510      >>> os.environ['TZ'] = 'EST+05EDT,M4.1.0,M10.5.0'
511      >>> time.tzset()
512      >>> time.strftime('%X %x %Z')
513      '02:07:36 05/08/03 EDT'
514      >>> os.environ['TZ'] = 'AEST-10AEDT-11,M10.5.0,M3.5.0'
515      >>> time.tzset()
516      >>> time.strftime('%X %x %Z')
517      '16:08:12 05/08/03 AEST'
518
519   On many Unix systems (including \*BSD, Linux, Solaris, and Darwin), it is more
520   convenient to use the system's zoneinfo (:manpage:`tzfile(5)`)  database to
521   specify the timezone rules. To do this, set the  :envvar:`TZ` environment
522   variable to the path of the required timezone  datafile, relative to the root of
523   the systems 'zoneinfo' timezone database, usually located at
524   :file:`/usr/share/zoneinfo`. For example,  ``'US/Eastern'``,
525   ``'Australia/Melbourne'``, ``'Egypt'`` or  ``'Europe/Amsterdam'``. ::
526
527      >>> os.environ['TZ'] = 'US/Eastern'
528      >>> time.tzset()
529      >>> time.tzname
530      ('EST', 'EDT')
531      >>> os.environ['TZ'] = 'Egypt'
532      >>> time.tzset()
533      >>> time.tzname
534      ('EET', 'EEST')
535
536
537.. seealso::
538
539   Module :mod:`datetime`
540      More object-oriented interface to dates and times.
541
542   Module :mod:`locale`
543      Internationalization services.  The locale settings can affect the return values
544      for some of  the functions in the :mod:`time` module.
545
546   Module :mod:`calendar`
547      General calendar-related functions.   :func:`timegm` is the inverse of
548      :func:`gmtime` from this module.
549
550.. rubric:: Footnotes
551
552.. [#] The use of ``%Z`` is now deprecated, but the ``%z`` escape that expands to the
553   preferred  hour/minute offset is not supported by all ANSI C libraries. Also, a
554   strict reading of the original 1982 :rfc:`822` standard calls for a two-digit
555   year (%y rather than %Y), but practice moved to 4-digit years long before the
556   year 2000.  The 4-digit year has been mandated by :rfc:`2822`, which obsoletes
557   :rfc:`822`.
558