1:mod:`time` --- Time access and conversions 2=========================================== 3 4.. module:: time 5 :synopsis: Time access and conversions. 6 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.. _epoch: 21 22.. index:: single: epoch 23 24* The :dfn:`epoch` is the point where the time starts, and is platform 25 dependent. For Unix, the epoch is January 1, 1970, 00:00:00 (UTC). 26 To find out what the epoch is on a given platform, look at 27 ``time.gmtime(0)``. 28 29.. _leap seconds: https://en.wikipedia.org/wiki/Leap_second 30 31.. index:: seconds since the epoch 32 33* The term :dfn:`seconds since the epoch` refers to the total number 34 of elapsed seconds since the epoch, typically excluding 35 `leap seconds`_. Leap seconds are excluded from this total on all 36 POSIX-compliant platforms. 37 38.. index:: single: Year 2038 39 40* The functions in this module may not handle dates and times before the epoch or 41 far in the future. The cut-off point in the future is determined by the C 42 library; for 32-bit systems, it is typically in 2038. 43 44.. index:: 45 single: 2-digit years 46 47* Function :func:`strptime` can parse 2-digit years when given ``%y`` format 48 code. When 2-digit years are parsed, they are converted according to the POSIX 49 and ISO C standards: values 69--99 are mapped to 1969--1999, and values 0--68 50 are mapped to 2000--2068. 51 52.. index:: 53 single: UTC 54 single: Coordinated Universal Time 55 single: Greenwich Mean Time 56 57* UTC is Coordinated Universal Time (formerly known as Greenwich Mean Time, or 58 GMT). The acronym UTC is not a mistake but a compromise between English and 59 French. 60 61.. index:: single: Daylight Saving Time 62 63* DST is Daylight Saving Time, an adjustment of the timezone by (usually) one 64 hour during part of the year. DST rules are magic (determined by local law) and 65 can change from year to year. The C library has a table containing the local 66 rules (often it is read from a system file for flexibility) and is the only 67 source of True Wisdom in this respect. 68 69* The precision of the various real-time functions may be less than suggested by 70 the units in which their value or argument is expressed. E.g. on most Unix 71 systems, the clock "ticks" only 50 or 100 times a second. 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 :c:func:`gettimeofday` where available), and :func:`sleep` will accept a time 77 with a nonzero fraction (Unix :c:func:`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 See :class:`struct_time` for a description of these objects. 87 88 .. versionchanged:: 3.3 89 The :class:`struct_time` type was extended to provide the :attr:`tm_gmtoff` 90 and :attr:`tm_zone` attributes when platform supports corresponding 91 ``struct tm`` members. 92 93 .. versionchanged:: 3.6 94 The :class:`struct_time` attributes :attr:`tm_gmtoff` and :attr:`tm_zone` 95 are now available on all platforms. 96 97* Use the following functions to convert between time representations: 98 99 +-------------------------+-------------------------+-------------------------+ 100 | From | To | Use | 101 +=========================+=========================+=========================+ 102 | seconds since the epoch | :class:`struct_time` in | :func:`gmtime` | 103 | | UTC | | 104 +-------------------------+-------------------------+-------------------------+ 105 | seconds since the epoch | :class:`struct_time` in | :func:`localtime` | 106 | | local time | | 107 +-------------------------+-------------------------+-------------------------+ 108 | :class:`struct_time` in | seconds since the epoch | :func:`calendar.timegm` | 109 | UTC | | | 110 +-------------------------+-------------------------+-------------------------+ 111 | :class:`struct_time` in | seconds since the epoch | :func:`mktime` | 112 | local time | | | 113 +-------------------------+-------------------------+-------------------------+ 114 115 116.. _time-functions: 117 118Functions 119--------- 120 121.. function:: asctime([t]) 122 123 Convert a tuple or :class:`struct_time` representing a time as returned by 124 :func:`gmtime` or :func:`localtime` to a string of the following 125 form: ``'Sun Jun 20 23:21:05 1993'``. The day field is two characters long 126 and is space padded if the day is a single digit, 127 e.g.: ``'Wed Jun 9 04:26:40 1993'``. 128 129 If *t* is not provided, the current time as returned by :func:`localtime` 130 is used. Locale information is not used by :func:`asctime`. 131 132 .. note:: 133 134 Unlike the C function of the same name, :func:`asctime` does not add a 135 trailing newline. 136 137.. function:: pthread_getcpuclockid(thread_id) 138 139 Return the *clk_id* of the thread-specific CPU-time clock for the specified *thread_id*. 140 141 Use :func:`threading.get_ident` or the :attr:`~threading.Thread.ident` 142 attribute of :class:`threading.Thread` objects to get a suitable value 143 for *thread_id*. 144 145 .. warning:: 146 Passing an invalid or expired *thread_id* may result in 147 undefined behavior, such as segmentation fault. 148 149 .. availability:: Unix (see the man page for :manpage:`pthread_getcpuclockid(3)` for 150 further information). 151 152 .. versionadded:: 3.7 153 154.. function:: clock_getres(clk_id) 155 156 Return the resolution (precision) of the specified clock *clk_id*. Refer to 157 :ref:`time-clock-id-constants` for a list of accepted values for *clk_id*. 158 159 .. availability:: Unix. 160 161 .. versionadded:: 3.3 162 163 164.. function:: clock_gettime(clk_id) -> float 165 166 Return the time of the specified clock *clk_id*. Refer to 167 :ref:`time-clock-id-constants` for a list of accepted values for *clk_id*. 168 169 .. availability:: Unix. 170 171 .. versionadded:: 3.3 172 173 174.. function:: clock_gettime_ns(clk_id) -> int 175 176 Similar to :func:`clock_gettime` but return time as nanoseconds. 177 178 .. availability:: Unix. 179 180 .. versionadded:: 3.7 181 182 183.. function:: clock_settime(clk_id, time: float) 184 185 Set the time of the specified clock *clk_id*. Currently, 186 :data:`CLOCK_REALTIME` is the only accepted value for *clk_id*. 187 188 .. availability:: Unix. 189 190 .. versionadded:: 3.3 191 192 193.. function:: clock_settime_ns(clk_id, time: int) 194 195 Similar to :func:`clock_settime` but set time with nanoseconds. 196 197 .. availability:: Unix. 198 199 .. versionadded:: 3.7 200 201 202.. function:: ctime([secs]) 203 204 Convert a time expressed in seconds since the epoch to a string of a form: 205 ``'Sun Jun 20 23:21:05 1993'`` representing local time. The day field 206 is two characters long and is space padded if the day is a single digit, 207 e.g.: ``'Wed Jun 9 04:26:40 1993'``. 208 209 If *secs* is not provided or :const:`None`, the current time as 210 returned by :func:`.time` is used. ``ctime(secs)`` is equivalent to 211 ``asctime(localtime(secs))``. Locale information is not used by 212 :func:`ctime`. 213 214 215.. function:: get_clock_info(name) 216 217 Get information on the specified clock as a namespace object. 218 Supported clock names and the corresponding functions to read their value 219 are: 220 221 * ``'monotonic'``: :func:`time.monotonic` 222 * ``'perf_counter'``: :func:`time.perf_counter` 223 * ``'process_time'``: :func:`time.process_time` 224 * ``'thread_time'``: :func:`time.thread_time` 225 * ``'time'``: :func:`time.time` 226 227 The result has the following attributes: 228 229 - *adjustable*: ``True`` if the clock can be changed automatically (e.g. by 230 a NTP daemon) or manually by the system administrator, ``False`` otherwise 231 - *implementation*: The name of the underlying C function used to get 232 the clock value. Refer to :ref:`time-clock-id-constants` for possible values. 233 - *monotonic*: ``True`` if the clock cannot go backward, 234 ``False`` otherwise 235 - *resolution*: The resolution of the clock in seconds (:class:`float`) 236 237 .. versionadded:: 3.3 238 239 240.. function:: gmtime([secs]) 241 242 Convert a time expressed in seconds since the epoch to a :class:`struct_time` in 243 UTC in which the dst flag is always zero. If *secs* is not provided or 244 :const:`None`, the current time as returned by :func:`.time` is used. Fractions 245 of a second are ignored. See above for a description of the 246 :class:`struct_time` object. See :func:`calendar.timegm` for the inverse of this 247 function. 248 249 250.. function:: localtime([secs]) 251 252 Like :func:`gmtime` but converts to local time. If *secs* is not provided or 253 :const:`None`, the current time as returned by :func:`.time` is used. The dst 254 flag is set to ``1`` when DST applies to the given time. 255 256 257.. function:: mktime(t) 258 259 This is the inverse function of :func:`localtime`. Its argument is the 260 :class:`struct_time` or full 9-tuple (since the dst flag is needed; use ``-1`` 261 as the dst flag if it is unknown) which expresses the time in *local* time, not 262 UTC. It returns a floating point number, for compatibility with :func:`.time`. 263 If the input value cannot be represented as a valid time, either 264 :exc:`OverflowError` or :exc:`ValueError` will be raised (which depends on 265 whether the invalid value is caught by Python or the underlying C libraries). 266 The earliest date for which it can generate a time is platform-dependent. 267 268 269.. function:: monotonic() -> float 270 271 Return the value (in fractional seconds) of a monotonic clock, i.e. a clock 272 that cannot go backwards. The clock is not affected by system clock updates. 273 The reference point of the returned value is undefined, so that only the 274 difference between the results of consecutive calls is valid. 275 276 .. versionadded:: 3.3 277 .. versionchanged:: 3.5 278 The function is now always available and always system-wide. 279 280 281.. function:: monotonic_ns() -> int 282 283 Similar to :func:`monotonic`, but return time as nanoseconds. 284 285 .. versionadded:: 3.7 286 287.. function:: perf_counter() -> float 288 289 .. index:: 290 single: benchmarking 291 292 Return the value (in fractional seconds) of a performance counter, i.e. a 293 clock with the highest available resolution to measure a short duration. It 294 does include time elapsed during sleep and is system-wide. The reference 295 point of the returned value is undefined, so that only the difference between 296 the results of consecutive calls is valid. 297 298 .. versionadded:: 3.3 299 300.. function:: perf_counter_ns() -> int 301 302 Similar to :func:`perf_counter`, but return time as nanoseconds. 303 304 .. versionadded:: 3.7 305 306 307.. function:: process_time() -> float 308 309 .. index:: 310 single: CPU time 311 single: processor time 312 single: benchmarking 313 314 Return the value (in fractional seconds) of the sum of the system and user 315 CPU time of the current process. It does not include time elapsed during 316 sleep. It is process-wide by definition. The reference point of the 317 returned value is undefined, so that only the difference between the results 318 of consecutive calls is valid. 319 320 .. versionadded:: 3.3 321 322.. function:: process_time_ns() -> int 323 324 Similar to :func:`process_time` but return time as nanoseconds. 325 326 .. versionadded:: 3.7 327 328.. function:: sleep(secs) 329 330 Suspend execution of the calling thread for the given number of seconds. 331 The argument may be a floating point number to indicate a more precise sleep 332 time. The actual suspension time may be less than that requested because any 333 caught signal will terminate the :func:`sleep` following execution of that 334 signal's catching routine. Also, the suspension time may be longer than 335 requested by an arbitrary amount because of the scheduling of other activity 336 in the system. 337 338 .. versionchanged:: 3.5 339 The function now sleeps at least *secs* even if the sleep is interrupted 340 by a signal, except if the signal handler raises an exception (see 341 :pep:`475` for the rationale). 342 343 344.. index:: 345 single: % (percent); datetime format 346 347.. function:: strftime(format[, t]) 348 349 Convert a tuple or :class:`struct_time` representing a time as returned by 350 :func:`gmtime` or :func:`localtime` to a string as specified by the *format* 351 argument. If *t* is not provided, the current time as returned by 352 :func:`localtime` is used. *format* must be a string. :exc:`ValueError` is 353 raised if any field in *t* is outside of the allowed range. 354 355 0 is a legal argument for any position in the time tuple; if it is normally 356 illegal the value is forced to a correct one. 357 358 The following directives can be embedded in the *format* string. They are shown 359 without the optional field width and precision specification, and are replaced 360 by the indicated characters in the :func:`strftime` result: 361 362 +-----------+------------------------------------------------+-------+ 363 | Directive | Meaning | Notes | 364 +===========+================================================+=======+ 365 | ``%a`` | Locale's abbreviated weekday name. | | 366 | | | | 367 +-----------+------------------------------------------------+-------+ 368 | ``%A`` | Locale's full weekday name. | | 369 +-----------+------------------------------------------------+-------+ 370 | ``%b`` | Locale's abbreviated month name. | | 371 | | | | 372 +-----------+------------------------------------------------+-------+ 373 | ``%B`` | Locale's full month name. | | 374 +-----------+------------------------------------------------+-------+ 375 | ``%c`` | Locale's appropriate date and time | | 376 | | representation. | | 377 +-----------+------------------------------------------------+-------+ 378 | ``%d`` | Day of the month as a decimal number [01,31]. | | 379 | | | | 380 +-----------+------------------------------------------------+-------+ 381 | ``%H`` | Hour (24-hour clock) as a decimal number | | 382 | | [00,23]. | | 383 +-----------+------------------------------------------------+-------+ 384 | ``%I`` | Hour (12-hour clock) as a decimal number | | 385 | | [01,12]. | | 386 +-----------+------------------------------------------------+-------+ 387 | ``%j`` | Day of the year as a decimal number [001,366]. | | 388 | | | | 389 +-----------+------------------------------------------------+-------+ 390 | ``%m`` | Month as a decimal number [01,12]. | | 391 | | | | 392 +-----------+------------------------------------------------+-------+ 393 | ``%M`` | Minute as a decimal number [00,59]. | | 394 | | | | 395 +-----------+------------------------------------------------+-------+ 396 | ``%p`` | Locale's equivalent of either AM or PM. | \(1) | 397 | | | | 398 +-----------+------------------------------------------------+-------+ 399 | ``%S`` | Second as a decimal number [00,61]. | \(2) | 400 | | | | 401 +-----------+------------------------------------------------+-------+ 402 | ``%U`` | Week number of the year (Sunday as the first | \(3) | 403 | | day of the week) as a decimal number [00,53]. | | 404 | | All days in a new year preceding the first | | 405 | | Sunday are considered to be in week 0. | | 406 | | | | 407 | | | | 408 | | | | 409 +-----------+------------------------------------------------+-------+ 410 | ``%w`` | Weekday as a decimal number [0(Sunday),6]. | | 411 | | | | 412 +-----------+------------------------------------------------+-------+ 413 | ``%W`` | Week number of the year (Monday as the first | \(3) | 414 | | day of the week) as a decimal number [00,53]. | | 415 | | All days in a new year preceding the first | | 416 | | Monday are considered to be in week 0. | | 417 | | | | 418 | | | | 419 | | | | 420 +-----------+------------------------------------------------+-------+ 421 | ``%x`` | Locale's appropriate date representation. | | 422 | | | | 423 +-----------+------------------------------------------------+-------+ 424 | ``%X`` | Locale's appropriate time representation. | | 425 | | | | 426 +-----------+------------------------------------------------+-------+ 427 | ``%y`` | Year without century as a decimal number | | 428 | | [00,99]. | | 429 +-----------+------------------------------------------------+-------+ 430 | ``%Y`` | Year with century as a decimal number. | | 431 | | | | 432 +-----------+------------------------------------------------+-------+ 433 | ``%z`` | Time zone offset indicating a positive or | | 434 | | negative time difference from UTC/GMT of the | | 435 | | form +HHMM or -HHMM, where H represents decimal| | 436 | | hour digits and M represents decimal minute | | 437 | | digits [-23:59, +23:59]. | | 438 +-----------+------------------------------------------------+-------+ 439 | ``%Z`` | Time zone name (no characters if no time zone | | 440 | | exists). | | 441 +-----------+------------------------------------------------+-------+ 442 | ``%%`` | A literal ``'%'`` character. | | 443 +-----------+------------------------------------------------+-------+ 444 445 Notes: 446 447 (1) 448 When used with the :func:`strptime` function, the ``%p`` directive only affects 449 the output hour field if the ``%I`` directive is used to parse the hour. 450 451 (2) 452 The range really is ``0`` to ``61``; value ``60`` is valid in 453 timestamps representing `leap seconds`_ and value ``61`` is supported 454 for historical reasons. 455 456 (3) 457 When used with the :func:`strptime` function, ``%U`` and ``%W`` are only used in 458 calculations when the day of the week and the year are specified. 459 460 Here is an example, a format for dates compatible with that specified in the 461 :rfc:`2822` Internet email standard. [#]_ :: 462 463 >>> from time import gmtime, strftime 464 >>> strftime("%a, %d %b %Y %H:%M:%S +0000", gmtime()) 465 'Thu, 28 Jun 2001 14:17:15 +0000' 466 467 Additional directives may be supported on certain platforms, but only the 468 ones listed here have a meaning standardized by ANSI C. To see the full set 469 of format codes supported on your platform, consult the :manpage:`strftime(3)` 470 documentation. 471 472 On some platforms, an optional field width and precision specification can 473 immediately follow the initial ``'%'`` of a directive in the following order; 474 this is also not portable. The field width is normally 2 except for ``%j`` where 475 it is 3. 476 477 478.. index:: 479 single: % (percent); datetime format 480 481.. function:: strptime(string[, format]) 482 483 Parse a string representing a time according to a format. The return value 484 is a :class:`struct_time` as returned by :func:`gmtime` or 485 :func:`localtime`. 486 487 The *format* parameter uses the same directives as those used by 488 :func:`strftime`; it defaults to ``"%a %b %d %H:%M:%S %Y"`` which matches the 489 formatting returned by :func:`ctime`. If *string* cannot be parsed according 490 to *format*, or if it has excess data after parsing, :exc:`ValueError` is 491 raised. The default values used to fill in any missing data when more 492 accurate values cannot be inferred are ``(1900, 1, 1, 0, 0, 0, 0, 1, -1)``. 493 Both *string* and *format* must be strings. 494 495 For example: 496 497 >>> import time 498 >>> time.strptime("30 Nov 00", "%d %b %y") # doctest: +NORMALIZE_WHITESPACE 499 time.struct_time(tm_year=2000, tm_mon=11, tm_mday=30, tm_hour=0, tm_min=0, 500 tm_sec=0, tm_wday=3, tm_yday=335, tm_isdst=-1) 501 502 Support for the ``%Z`` directive is based on the values contained in ``tzname`` 503 and whether ``daylight`` is true. Because of this, it is platform-specific 504 except for recognizing UTC and GMT which are always known (and are considered to 505 be non-daylight savings timezones). 506 507 Only the directives specified in the documentation are supported. Because 508 ``strftime()`` is implemented per platform it can sometimes offer more 509 directives than those listed. But ``strptime()`` is independent of any platform 510 and thus does not necessarily support all directives available that are not 511 documented as supported. 512 513 514.. class:: struct_time 515 516 The type of the time value sequence returned by :func:`gmtime`, 517 :func:`localtime`, and :func:`strptime`. It is an object with a :term:`named 518 tuple` interface: values can be accessed by index and by attribute name. The 519 following values are present: 520 521 +-------+-------------------+---------------------------------+ 522 | Index | Attribute | Values | 523 +=======+===================+=================================+ 524 | 0 | :attr:`tm_year` | (for example, 1993) | 525 +-------+-------------------+---------------------------------+ 526 | 1 | :attr:`tm_mon` | range [1, 12] | 527 +-------+-------------------+---------------------------------+ 528 | 2 | :attr:`tm_mday` | range [1, 31] | 529 +-------+-------------------+---------------------------------+ 530 | 3 | :attr:`tm_hour` | range [0, 23] | 531 +-------+-------------------+---------------------------------+ 532 | 4 | :attr:`tm_min` | range [0, 59] | 533 +-------+-------------------+---------------------------------+ 534 | 5 | :attr:`tm_sec` | range [0, 61]; see **(2)** in | 535 | | | :func:`strftime` description | 536 +-------+-------------------+---------------------------------+ 537 | 6 | :attr:`tm_wday` | range [0, 6], Monday is 0 | 538 +-------+-------------------+---------------------------------+ 539 | 7 | :attr:`tm_yday` | range [1, 366] | 540 +-------+-------------------+---------------------------------+ 541 | 8 | :attr:`tm_isdst` | 0, 1 or -1; see below | 542 +-------+-------------------+---------------------------------+ 543 | N/A | :attr:`tm_zone` | abbreviation of timezone name | 544 +-------+-------------------+---------------------------------+ 545 | N/A | :attr:`tm_gmtoff` | offset east of UTC in seconds | 546 +-------+-------------------+---------------------------------+ 547 548 Note that unlike the C structure, the month value is a range of [1, 12], not 549 [0, 11]. 550 551 In calls to :func:`mktime`, :attr:`tm_isdst` may be set to 1 when daylight 552 savings time is in effect, and 0 when it is not. A value of -1 indicates that 553 this is not known, and will usually result in the correct state being filled in. 554 555 When a tuple with an incorrect length is passed to a function expecting a 556 :class:`struct_time`, or having elements of the wrong type, a 557 :exc:`TypeError` is raised. 558 559.. function:: time() -> float 560 561 Return the time in seconds since the epoch_ as a floating point 562 number. The specific date of the epoch and the handling of 563 `leap seconds`_ is platform dependent. 564 On Windows and most Unix systems, the epoch is January 1, 1970, 565 00:00:00 (UTC) and leap seconds are not counted towards the time 566 in seconds since the epoch. This is commonly referred to as 567 `Unix time <https://en.wikipedia.org/wiki/Unix_time>`_. 568 To find out what the epoch is on a given platform, look at 569 ``gmtime(0)``. 570 571 Note that even though the time is always returned as a floating point 572 number, not all systems provide time with a better precision than 1 second. 573 While this function normally returns non-decreasing values, it can return a 574 lower value than a previous call if the system clock has been set back 575 between the two calls. 576 577 The number returned by :func:`.time` may be converted into a more common 578 time format (i.e. year, month, day, hour, etc...) in UTC by passing it to 579 :func:`gmtime` function or in local time by passing it to the 580 :func:`localtime` function. In both cases a 581 :class:`struct_time` object is returned, from which the components 582 of the calendar date may be accessed as attributes. 583 584 585.. function:: thread_time() -> float 586 587 .. index:: 588 single: CPU time 589 single: processor time 590 single: benchmarking 591 592 Return the value (in fractional seconds) of the sum of the system and user 593 CPU time of the current thread. It does not include time elapsed during 594 sleep. It is thread-specific by definition. The reference point of the 595 returned value is undefined, so that only the difference between the results 596 of consecutive calls in the same thread is valid. 597 598 .. availability:: Windows, Linux, Unix systems supporting 599 ``CLOCK_THREAD_CPUTIME_ID``. 600 601 .. versionadded:: 3.7 602 603 604.. function:: thread_time_ns() -> int 605 606 Similar to :func:`thread_time` but return time as nanoseconds. 607 608 .. versionadded:: 3.7 609 610 611.. function:: time_ns() -> int 612 613 Similar to :func:`~time.time` but returns time as an integer number of nanoseconds 614 since the epoch_. 615 616 .. versionadded:: 3.7 617 618.. function:: tzset() 619 620 Reset the time conversion rules used by the library routines. The environment 621 variable :envvar:`TZ` specifies how this is done. It will also set the variables 622 ``tzname`` (from the :envvar:`TZ` environment variable), ``timezone`` (non-DST 623 seconds West of UTC), ``altzone`` (DST seconds west of UTC) and ``daylight`` 624 (to 0 if this timezone does not have any daylight saving time rules, or to 625 nonzero if there is a time, past, present or future when daylight saving time 626 applies). 627 628 .. availability:: Unix. 629 630 .. note:: 631 632 Although in many cases, changing the :envvar:`TZ` environment variable may 633 affect the output of functions like :func:`localtime` without calling 634 :func:`tzset`, this behavior should not be relied on. 635 636 The :envvar:`TZ` environment variable should contain no whitespace. 637 638 The standard format of the :envvar:`TZ` environment variable is (whitespace 639 added for clarity):: 640 641 std offset [dst [offset [,start[/time], end[/time]]]] 642 643 Where the components are: 644 645 ``std`` and ``dst`` 646 Three or more alphanumerics giving the timezone abbreviations. These will be 647 propagated into time.tzname 648 649 ``offset`` 650 The offset has the form: ``± hh[:mm[:ss]]``. This indicates the value 651 added the local time to arrive at UTC. If preceded by a '-', the timezone 652 is east of the Prime Meridian; otherwise, it is west. If no offset follows 653 dst, summer time is assumed to be one hour ahead of standard time. 654 655 ``start[/time], end[/time]`` 656 Indicates when to change to and back from DST. The format of the 657 start and end dates are one of the following: 658 659 :samp:`J{n}` 660 The Julian day *n* (1 <= *n* <= 365). Leap days are not counted, so in 661 all years February 28 is day 59 and March 1 is day 60. 662 663 :samp:`{n}` 664 The zero-based Julian day (0 <= *n* <= 365). Leap days are counted, and 665 it is possible to refer to February 29. 666 667 :samp:`M{m}.{n}.{d}` 668 The *d*'th day (0 <= *d* <= 6) of week *n* of month *m* of the year (1 669 <= *n* <= 5, 1 <= *m* <= 12, where week 5 means "the last *d* day in 670 month *m*" which may occur in either the fourth or the fifth 671 week). Week 1 is the first week in which the *d*'th day occurs. Day 672 zero is a Sunday. 673 674 ``time`` has the same format as ``offset`` except that no leading sign 675 ('-' or '+') is allowed. The default, if time is not given, is 02:00:00. 676 677 :: 678 679 >>> os.environ['TZ'] = 'EST+05EDT,M4.1.0,M10.5.0' 680 >>> time.tzset() 681 >>> time.strftime('%X %x %Z') 682 '02:07:36 05/08/03 EDT' 683 >>> os.environ['TZ'] = 'AEST-10AEDT-11,M10.5.0,M3.5.0' 684 >>> time.tzset() 685 >>> time.strftime('%X %x %Z') 686 '16:08:12 05/08/03 AEST' 687 688 On many Unix systems (including \*BSD, Linux, Solaris, and Darwin), it is more 689 convenient to use the system's zoneinfo (:manpage:`tzfile(5)`) database to 690 specify the timezone rules. To do this, set the :envvar:`TZ` environment 691 variable to the path of the required timezone datafile, relative to the root of 692 the systems 'zoneinfo' timezone database, usually located at 693 :file:`/usr/share/zoneinfo`. For example, ``'US/Eastern'``, 694 ``'Australia/Melbourne'``, ``'Egypt'`` or ``'Europe/Amsterdam'``. :: 695 696 >>> os.environ['TZ'] = 'US/Eastern' 697 >>> time.tzset() 698 >>> time.tzname 699 ('EST', 'EDT') 700 >>> os.environ['TZ'] = 'Egypt' 701 >>> time.tzset() 702 >>> time.tzname 703 ('EET', 'EEST') 704 705 706.. _time-clock-id-constants: 707 708Clock ID Constants 709------------------ 710 711These constants are used as parameters for :func:`clock_getres` and 712:func:`clock_gettime`. 713 714.. data:: CLOCK_BOOTTIME 715 716 Identical to :data:`CLOCK_MONOTONIC`, except it also includes any time that 717 the system is suspended. 718 719 This allows applications to get a suspend-aware monotonic clock without 720 having to deal with the complications of :data:`CLOCK_REALTIME`, which may 721 have discontinuities if the time is changed using ``settimeofday()`` or 722 similar. 723 724 .. availability:: Linux 2.6.39 or later. 725 726 .. versionadded:: 3.7 727 728 729.. data:: CLOCK_HIGHRES 730 731 The Solaris OS has a ``CLOCK_HIGHRES`` timer that attempts to use an optimal 732 hardware source, and may give close to nanosecond resolution. 733 ``CLOCK_HIGHRES`` is the nonadjustable, high-resolution clock. 734 735 .. availability:: Solaris. 736 737 .. versionadded:: 3.3 738 739 740.. data:: CLOCK_MONOTONIC 741 742 Clock that cannot be set and represents monotonic time since some unspecified 743 starting point. 744 745 .. availability:: Unix. 746 747 .. versionadded:: 3.3 748 749 750.. data:: CLOCK_MONOTONIC_RAW 751 752 Similar to :data:`CLOCK_MONOTONIC`, but provides access to a raw 753 hardware-based time that is not subject to NTP adjustments. 754 755 .. availability:: Linux 2.6.28 and newer, macOS 10.12 and newer. 756 757 .. versionadded:: 3.3 758 759 760.. data:: CLOCK_PROCESS_CPUTIME_ID 761 762 High-resolution per-process timer from the CPU. 763 764 .. availability:: Unix. 765 766 .. versionadded:: 3.3 767 768 769.. data:: CLOCK_PROF 770 771 High-resolution per-process timer from the CPU. 772 773 .. availability:: FreeBSD, NetBSD 7 or later, OpenBSD. 774 775 .. versionadded:: 3.7 776 777.. data:: CLOCK_TAI 778 779 `International Atomic Time <https://www.nist.gov/pml/time-and-frequency-division/nist-time-frequently-asked-questions-faq#tai>`_ 780 781 The system must have a current leap second table in order for this to give 782 the correct answer. PTP or NTP software can maintain a leap second table. 783 784 .. availability:: Linux. 785 786 .. versionadded:: 3.9 787 788.. data:: CLOCK_THREAD_CPUTIME_ID 789 790 Thread-specific CPU-time clock. 791 792 .. availability:: Unix. 793 794 .. versionadded:: 3.3 795 796 797.. data:: CLOCK_UPTIME 798 799 Time whose absolute value is the time the system has been running and not 800 suspended, providing accurate uptime measurement, both absolute and 801 interval. 802 803 .. availability:: FreeBSD, OpenBSD 5.5 or later. 804 805 .. versionadded:: 3.7 806 807 808.. data:: CLOCK_UPTIME_RAW 809 810 Clock that increments monotonically, tracking the time since an arbitrary 811 point, unaffected by frequency or time adjustments and not incremented while 812 the system is asleep. 813 814 .. availability:: macOS 10.12 and newer. 815 816 .. versionadded:: 3.8 817 818The following constant is the only parameter that can be sent to 819:func:`clock_settime`. 820 821 822.. data:: CLOCK_REALTIME 823 824 System-wide real-time clock. Setting this clock requires appropriate 825 privileges. 826 827 .. availability:: Unix. 828 829 .. versionadded:: 3.3 830 831 832.. _time-timezone-constants: 833 834Timezone Constants 835------------------- 836 837.. data:: altzone 838 839 The offset of the local DST timezone, in seconds west of UTC, if one is defined. 840 This is negative if the local DST timezone is east of UTC (as in Western Europe, 841 including the UK). Only use this if ``daylight`` is nonzero. See note below. 842 843.. data:: daylight 844 845 Nonzero if a DST timezone is defined. See note below. 846 847.. data:: timezone 848 849 The offset of the local (non-DST) timezone, in seconds west of UTC (negative in 850 most of Western Europe, positive in the US, zero in the UK). See note below. 851 852.. data:: tzname 853 854 A tuple of two strings: the first is the name of the local non-DST timezone, the 855 second is the name of the local DST timezone. If no DST timezone is defined, 856 the second string should not be used. See note below. 857 858.. note:: 859 860 For the above Timezone constants (:data:`altzone`, :data:`daylight`, :data:`timezone`, 861 and :data:`tzname`), the value is determined by the timezone rules in effect 862 at module load time or the last time :func:`tzset` is called and may be incorrect 863 for times in the past. It is recommended to use the :attr:`tm_gmtoff` and 864 :attr:`tm_zone` results from :func:`localtime` to obtain timezone information. 865 866 867.. seealso:: 868 869 Module :mod:`datetime` 870 More object-oriented interface to dates and times. 871 872 Module :mod:`locale` 873 Internationalization services. The locale setting affects the interpretation 874 of many format specifiers in :func:`strftime` and :func:`strptime`. 875 876 Module :mod:`calendar` 877 General calendar-related functions. :func:`~calendar.timegm` is the 878 inverse of :func:`gmtime` from this module. 879 880.. rubric:: Footnotes 881 882.. [#] The use of ``%Z`` is now deprecated, but the ``%z`` escape that expands to the 883 preferred hour/minute offset is not supported by all ANSI C libraries. Also, a 884 strict reading of the original 1982 :rfc:`822` standard calls for a two-digit 885 year (%y rather than %Y), but practice moved to 4-digit years long before the 886 year 2000. After that, :rfc:`822` became obsolete and the 4-digit year has 887 been first recommended by :rfc:`1123` and then mandated by :rfc:`2822`. 888 889