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