1 :mod:`time` --- Time access and conversions 2 =========================================== 3 4 .. module:: time 5 :synopsis: Time access and conversions. 6 7 -------------- 8 9 This module provides various time-related functions. For related 10 functionality, see also the :mod:`datetime` and :mod:`calendar` modules. 11 12 Although this module is always available, 13 not all functions are available on all platforms. Most of the functions 14 defined in this module call platform C library functions with the same name. It 15 may sometimes be helpful to consult the platform documentation, because the 16 semantics of these functions varies among platforms. 17 18 An 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: Year 2000 46 single: Y2K 47 48 .. _time-y2kissues: 49 50 * **Year 2000 (Y2K) issues**: Python depends on the platform's C library, which 51 generally doesn't have year 2000 issues, since all dates and times are 52 represented internally as seconds since the epoch. Function :func:`strptime` 53 can parse 2-digit years when given ``%y`` format code. When 2-digit years are 54 parsed, they are converted according to the POSIX and ISO C standards: values 55 69--99 are mapped to 1969--1999, and values 0--68 are mapped to 2000--2068. 56 57 .. index:: 58 single: UTC 59 single: Coordinated Universal Time 60 single: Greenwich Mean Time 61 62 * UTC is Coordinated Universal Time (formerly known as Greenwich Mean Time, or 63 GMT). The acronym UTC is not a mistake but a compromise between English and 64 French. 65 66 .. index:: single: Daylight Saving Time 67 68 * DST is Daylight Saving Time, an adjustment of the timezone by (usually) one 69 hour during part of the year. DST rules are magic (determined by local law) and 70 can change from year to year. The C library has a table containing the local 71 rules (often it is read from a system file for flexibility) and is the only 72 source of True Wisdom in this respect. 73 74 * The precision of the various real-time functions may be less than suggested by 75 the units in which their value or argument is expressed. E.g. on most Unix 76 systems, the clock "ticks" only 50 or 100 times a second. 77 78 * On the other hand, the precision of :func:`.time` and :func:`sleep` is better 79 than their Unix equivalents: times are expressed as floating point numbers, 80 :func:`.time` returns the most accurate time available (using Unix 81 :c:func:`gettimeofday` where available), and :func:`sleep` will accept a time 82 with a nonzero fraction (Unix :c:func:`select` is used to implement this, where 83 available). 84 85 * The time value as returned by :func:`gmtime`, :func:`localtime`, and 86 :func:`strptime`, and accepted by :func:`asctime`, :func:`mktime` and 87 :func:`strftime`, is a sequence of 9 integers. The return values of 88 :func:`gmtime`, :func:`localtime`, and :func:`strptime` also offer attribute 89 names for individual fields. 90 91 See :class:`struct_time` for a description of these objects. 92 93 .. versionchanged:: 3.3 94 The :class:`struct_time` type was extended to provide the :attr:`tm_gmtoff` 95 and :attr:`tm_zone` attributes when platform supports corresponding 96 ``struct tm`` members. 97 98 .. versionchanged:: 3.6 99 The :class:`struct_time` attributes :attr:`tm_gmtoff` and :attr:`tm_zone` 100 are now available on all platforms. 101 102 * Use the following functions to convert between time representations: 103 104 +-------------------------+-------------------------+-------------------------+ 105 | From | To | Use | 106 +=========================+=========================+=========================+ 107 | seconds since the epoch | :class:`struct_time` in | :func:`gmtime` | 108 | | UTC | | 109 +-------------------------+-------------------------+-------------------------+ 110 | seconds since the epoch | :class:`struct_time` in | :func:`localtime` | 111 | | local time | | 112 +-------------------------+-------------------------+-------------------------+ 113 | :class:`struct_time` in | seconds since the epoch | :func:`calendar.timegm` | 114 | UTC | | | 115 +-------------------------+-------------------------+-------------------------+ 116 | :class:`struct_time` in | seconds since the epoch | :func:`mktime` | 117 | local time | | | 118 +-------------------------+-------------------------+-------------------------+ 119 120 121 The module defines the following functions and data items: 122 123 .. data:: altzone 124 125 The offset of the local DST timezone, in seconds west of UTC, if one is defined. 126 This is negative if the local DST timezone is east of UTC (as in Western Europe, 127 including the UK). Only use this if ``daylight`` is nonzero. 128 129 130 .. function:: asctime([t]) 131 132 Convert a tuple or :class:`struct_time` representing a time as returned by 133 :func:`gmtime` or :func:`localtime` to a string of the following 134 form: ``'Sun Jun 20 23:21:05 1993'``. If *t* is not provided, the current time 135 as returned by :func:`localtime` is used. Locale information is not used by 136 :func:`asctime`. 137 138 .. note:: 139 140 Unlike the C function of the same name, :func:`asctime` does not add a 141 trailing newline. 142 143 144 .. function:: clock() 145 146 .. index:: 147 single: CPU time 148 single: processor time 149 single: benchmarking 150 151 On Unix, return the current processor time as a floating point number expressed 152 in seconds. The precision, and in fact the very definition of the meaning of 153 "processor time", depends on that of the C function of the same name. 154 155 On Windows, this function returns wall-clock seconds elapsed since the first 156 call to this function, as a floating point number, based on the Win32 function 157 :c:func:`QueryPerformanceCounter`. The resolution is typically better than one 158 microsecond. 159 160 .. deprecated:: 3.3 161 The behaviour of this function depends on the platform: use 162 :func:`perf_counter` or :func:`process_time` instead, depending on your 163 requirements, to have a well defined behaviour. 164 165 166 .. function:: clock_getres(clk_id) 167 168 Return the resolution (precision) of the specified clock *clk_id*. 169 170 Availability: Unix. 171 172 .. versionadded:: 3.3 173 174 175 .. function:: clock_gettime(clk_id) 176 177 Return the time of the specified clock *clk_id*. 178 179 Availability: Unix. 180 181 .. versionadded:: 3.3 182 183 184 .. function:: clock_settime(clk_id, time) 185 186 Set the time of the specified clock *clk_id*. 187 188 Availability: Unix. 189 190 .. versionadded:: 3.3 191 192 193 .. data:: CLOCK_HIGHRES 194 195 The Solaris OS has a CLOCK_HIGHRES timer that attempts to use an optimal 196 hardware source, and may give close to nanosecond resolution. CLOCK_HIGHRES 197 is the nonadjustable, high-resolution clock. 198 199 Availability: Solaris. 200 201 .. versionadded:: 3.3 202 203 204 .. data:: CLOCK_MONOTONIC 205 206 Clock that cannot be set and represents monotonic time since some unspecified 207 starting point. 208 209 Availability: Unix. 210 211 .. versionadded:: 3.3 212 213 214 .. data:: CLOCK_MONOTONIC_RAW 215 216 Similar to :data:`CLOCK_MONOTONIC`, but provides access to a raw 217 hardware-based time that is not subject to NTP adjustments. 218 219 Availability: Linux 2.6.28 or later. 220 221 .. versionadded:: 3.3 222 223 224 .. data:: CLOCK_PROCESS_CPUTIME_ID 225 226 High-resolution per-process timer from the CPU. 227 228 Availability: Unix. 229 230 .. versionadded:: 3.3 231 232 233 .. data:: CLOCK_REALTIME 234 235 System-wide real-time clock. Setting this clock requires appropriate 236 privileges. 237 238 Availability: Unix. 239 240 .. versionadded:: 3.3 241 242 243 .. data:: CLOCK_THREAD_CPUTIME_ID 244 245 Thread-specific CPU-time clock. 246 247 Availability: Unix. 248 249 .. versionadded:: 3.3 250 251 252 .. function:: ctime([secs]) 253 254 Convert a time expressed in seconds since the epoch to a string representing 255 local time. If *secs* is not provided or :const:`None`, the current time as 256 returned by :func:`.time` is used. ``ctime(secs)`` is equivalent to 257 ``asctime(localtime(secs))``. Locale information is not used by :func:`ctime`. 258 259 260 .. data:: daylight 261 262 Nonzero if a DST timezone is defined. 263 264 265 .. function:: get_clock_info(name) 266 267 Get information on the specified clock as a namespace object. 268 Supported clock names and the corresponding functions to read their value 269 are: 270 271 * ``'clock'``: :func:`time.clock` 272 * ``'monotonic'``: :func:`time.monotonic` 273 * ``'perf_counter'``: :func:`time.perf_counter` 274 * ``'process_time'``: :func:`time.process_time` 275 * ``'time'``: :func:`time.time` 276 277 The result has the following attributes: 278 279 - *adjustable*: ``True`` if the clock can be changed automatically (e.g. by 280 a NTP daemon) or manually by the system administrator, ``False`` otherwise 281 - *implementation*: The name of the underlying C function used to get 282 the clock value 283 - *monotonic*: ``True`` if the clock cannot go backward, 284 ``False`` otherwise 285 - *resolution*: The resolution of the clock in seconds (:class:`float`) 286 287 .. versionadded:: 3.3 288 289 290 .. function:: gmtime([secs]) 291 292 Convert a time expressed in seconds since the epoch to a :class:`struct_time` in 293 UTC in which the dst flag is always zero. If *secs* is not provided or 294 :const:`None`, the current time as returned by :func:`.time` is used. Fractions 295 of a second are ignored. See above for a description of the 296 :class:`struct_time` object. See :func:`calendar.timegm` for the inverse of this 297 function. 298 299 300 .. function:: localtime([secs]) 301 302 Like :func:`gmtime` but converts to local time. If *secs* is not provided or 303 :const:`None`, the current time as returned by :func:`.time` is used. The dst 304 flag is set to ``1`` when DST applies to the given time. 305 306 307 .. function:: mktime(t) 308 309 This is the inverse function of :func:`localtime`. Its argument is the 310 :class:`struct_time` or full 9-tuple (since the dst flag is needed; use ``-1`` 311 as the dst flag if it is unknown) which expresses the time in *local* time, not 312 UTC. It returns a floating point number, for compatibility with :func:`.time`. 313 If the input value cannot be represented as a valid time, either 314 :exc:`OverflowError` or :exc:`ValueError` will be raised (which depends on 315 whether the invalid value is caught by Python or the underlying C libraries). 316 The earliest date for which it can generate a time is platform-dependent. 317 318 319 .. function:: monotonic() 320 321 Return the value (in fractional seconds) of a monotonic clock, i.e. a clock 322 that cannot go backwards. The clock is not affected by system clock updates. 323 The reference point of the returned value is undefined, so that only the 324 difference between the results of consecutive calls is valid. 325 326 On Windows versions older than Vista, :func:`monotonic` detects 327 :c:func:`GetTickCount` integer overflow (32 bits, roll-over after 49.7 days). 328 It increases an internal epoch (reference time) by 2\ :sup:`32` each time 329 that an overflow is detected. The epoch is stored in the process-local state 330 and so the value of :func:`monotonic` may be different in two Python 331 processes running for more than 49 days. On more recent versions of Windows 332 and on other operating systems, :func:`monotonic` is system-wide. 333 334 .. versionadded:: 3.3 335 .. versionchanged:: 3.5 336 The function is now always available. 337 338 339 .. function:: perf_counter() 340 341 Return the value (in fractional seconds) of a performance counter, i.e. a 342 clock with the highest available resolution to measure a short duration. It 343 does include time elapsed during sleep and is system-wide. The reference 344 point of the returned value is undefined, so that only the difference between 345 the results of consecutive calls is valid. 346 347 .. versionadded:: 3.3 348 349 350 .. function:: process_time() 351 352 Return the value (in fractional seconds) of the sum of the system and user 353 CPU time of the current process. It does not include time elapsed during 354 sleep. It is process-wide by definition. The reference point of the 355 returned value is undefined, so that only the difference between the results 356 of consecutive calls is valid. 357 358 .. versionadded:: 3.3 359 360 .. function:: sleep(secs) 361 362 Suspend execution of the calling thread for the given number of seconds. 363 The argument may be a floating point number to indicate a more precise sleep 364 time. The actual suspension time may be less than that requested because any 365 caught signal will terminate the :func:`sleep` following execution of that 366 signal's catching routine. Also, the suspension time may be longer than 367 requested by an arbitrary amount because of the scheduling of other activity 368 in the system. 369 370 .. versionchanged:: 3.5 371 The function now sleeps at least *secs* even if the sleep is interrupted 372 by a signal, except if the signal handler raises an exception (see 373 :pep:`475` for the rationale). 374 375 376 .. function:: strftime(format[, t]) 377 378 Convert a tuple or :class:`struct_time` representing a time as returned by 379 :func:`gmtime` or :func:`localtime` to a string as specified by the *format* 380 argument. If *t* is not provided, the current time as returned by 381 :func:`localtime` is used. *format* must be a string. :exc:`ValueError` is 382 raised if any field in *t* is outside of the allowed range. 383 384 0 is a legal argument for any position in the time tuple; if it is normally 385 illegal the value is forced to a correct one. 386 387 The following directives can be embedded in the *format* string. They are shown 388 without the optional field width and precision specification, and are replaced 389 by the indicated characters in the :func:`strftime` result: 390 391 +-----------+------------------------------------------------+-------+ 392 | Directive | Meaning | Notes | 393 +===========+================================================+=======+ 394 | ``%a`` | Locale's abbreviated weekday name. | | 395 | | | | 396 +-----------+------------------------------------------------+-------+ 397 | ``%A`` | Locale's full weekday name. | | 398 +-----------+------------------------------------------------+-------+ 399 | ``%b`` | Locale's abbreviated month name. | | 400 | | | | 401 +-----------+------------------------------------------------+-------+ 402 | ``%B`` | Locale's full month name. | | 403 +-----------+------------------------------------------------+-------+ 404 | ``%c`` | Locale's appropriate date and time | | 405 | | representation. | | 406 +-----------+------------------------------------------------+-------+ 407 | ``%d`` | Day of the month as a decimal number [01,31]. | | 408 | | | | 409 +-----------+------------------------------------------------+-------+ 410 | ``%H`` | Hour (24-hour clock) as a decimal number | | 411 | | [00,23]. | | 412 +-----------+------------------------------------------------+-------+ 413 | ``%I`` | Hour (12-hour clock) as a decimal number | | 414 | | [01,12]. | | 415 +-----------+------------------------------------------------+-------+ 416 | ``%j`` | Day of the year as a decimal number [001,366]. | | 417 | | | | 418 +-----------+------------------------------------------------+-------+ 419 | ``%m`` | Month as a decimal number [01,12]. | | 420 | | | | 421 +-----------+------------------------------------------------+-------+ 422 | ``%M`` | Minute as a decimal number [00,59]. | | 423 | | | | 424 +-----------+------------------------------------------------+-------+ 425 | ``%p`` | Locale's equivalent of either AM or PM. | \(1) | 426 | | | | 427 +-----------+------------------------------------------------+-------+ 428 | ``%S`` | Second as a decimal number [00,61]. | \(2) | 429 | | | | 430 +-----------+------------------------------------------------+-------+ 431 | ``%U`` | Week number of the year (Sunday as the first | \(3) | 432 | | day of the week) as a decimal number [00,53]. | | 433 | | All days in a new year preceding the first | | 434 | | Sunday are considered to be in week 0. | | 435 | | | | 436 | | | | 437 | | | | 438 +-----------+------------------------------------------------+-------+ 439 | ``%w`` | Weekday as a decimal number [0(Sunday),6]. | | 440 | | | | 441 +-----------+------------------------------------------------+-------+ 442 | ``%W`` | Week number of the year (Monday as the first | \(3) | 443 | | day of the week) as a decimal number [00,53]. | | 444 | | All days in a new year preceding the first | | 445 | | Monday are considered to be in week 0. | | 446 | | | | 447 | | | | 448 | | | | 449 +-----------+------------------------------------------------+-------+ 450 | ``%x`` | Locale's appropriate date representation. | | 451 | | | | 452 +-----------+------------------------------------------------+-------+ 453 | ``%X`` | Locale's appropriate time representation. | | 454 | | | | 455 +-----------+------------------------------------------------+-------+ 456 | ``%y`` | Year without century as a decimal number | | 457 | | [00,99]. | | 458 +-----------+------------------------------------------------+-------+ 459 | ``%Y`` | Year with century as a decimal number. | | 460 | | | | 461 +-----------+------------------------------------------------+-------+ 462 | ``%z`` | Time zone offset indicating a positive or | | 463 | | negative time difference from UTC/GMT of the | | 464 | | form +HHMM or -HHMM, where H represents decimal| | 465 | | hour digits and M represents decimal minute | | 466 | | digits [-23:59, +23:59]. | | 467 +-----------+------------------------------------------------+-------+ 468 | ``%Z`` | Time zone name (no characters if no time zone | | 469 | | exists). | | 470 +-----------+------------------------------------------------+-------+ 471 | ``%%`` | A literal ``'%'`` character. | | 472 +-----------+------------------------------------------------+-------+ 473 474 Notes: 475 476 (1) 477 When used with the :func:`strptime` function, the ``%p`` directive only affects 478 the output hour field if the ``%I`` directive is used to parse the hour. 479 480 (2) 481 The range really is ``0`` to ``61``; value ``60`` is valid in 482 timestamps representing `leap seconds`_ and value ``61`` is supported 483 for historical reasons. 484 485 (3) 486 When used with the :func:`strptime` function, ``%U`` and ``%W`` are only used in 487 calculations when the day of the week and the year are specified. 488 489 Here is an example, a format for dates compatible with that specified in the 490 :rfc:`2822` Internet email standard. [#]_ :: 491 492 >>> from time import gmtime, strftime 493 >>> strftime("%a, %d %b %Y %H:%M:%S +0000", gmtime()) 494 'Thu, 28 Jun 2001 14:17:15 +0000' 495 496 Additional directives may be supported on certain platforms, but only the 497 ones listed here have a meaning standardized by ANSI C. To see the full set 498 of format codes supported on your platform, consult the :manpage:`strftime(3)` 499 documentation. 500 501 On some platforms, an optional field width and precision specification can 502 immediately follow the initial ``'%'`` of a directive in the following order; 503 this is also not portable. The field width is normally 2 except for ``%j`` where 504 it is 3. 505 506 507 .. function:: strptime(string[, format]) 508 509 Parse a string representing a time according to a format. The return value 510 is a :class:`struct_time` as returned by :func:`gmtime` or 511 :func:`localtime`. 512 513 The *format* parameter uses the same directives as those used by 514 :func:`strftime`; it defaults to ``"%a %b %d %H:%M:%S %Y"`` which matches the 515 formatting returned by :func:`ctime`. If *string* cannot be parsed according 516 to *format*, or if it has excess data after parsing, :exc:`ValueError` is 517 raised. The default values used to fill in any missing data when more 518 accurate values cannot be inferred are ``(1900, 1, 1, 0, 0, 0, 0, 1, -1)``. 519 Both *string* and *format* must be strings. 520 521 For example: 522 523 >>> import time 524 >>> time.strptime("30 Nov 00", "%d %b %y") # doctest: +NORMALIZE_WHITESPACE 525 time.struct_time(tm_year=2000, tm_mon=11, tm_mday=30, tm_hour=0, tm_min=0, 526 tm_sec=0, tm_wday=3, tm_yday=335, tm_isdst=-1) 527 528 Support for the ``%Z`` directive is based on the values contained in ``tzname`` 529 and whether ``daylight`` is true. Because of this, it is platform-specific 530 except for recognizing UTC and GMT which are always known (and are considered to 531 be non-daylight savings timezones). 532 533 Only the directives specified in the documentation are supported. Because 534 ``strftime()`` is implemented per platform it can sometimes offer more 535 directives than those listed. But ``strptime()`` is independent of any platform 536 and thus does not necessarily support all directives available that are not 537 documented as supported. 538 539 540 .. class:: struct_time 541 542 The type of the time value sequence returned by :func:`gmtime`, 543 :func:`localtime`, and :func:`strptime`. It is an object with a :term:`named 544 tuple` interface: values can be accessed by index and by attribute name. The 545 following values are present: 546 547 +-------+-------------------+---------------------------------+ 548 | Index | Attribute | Values | 549 +=======+===================+=================================+ 550 | 0 | :attr:`tm_year` | (for example, 1993) | 551 +-------+-------------------+---------------------------------+ 552 | 1 | :attr:`tm_mon` | range [1, 12] | 553 +-------+-------------------+---------------------------------+ 554 | 2 | :attr:`tm_mday` | range [1, 31] | 555 +-------+-------------------+---------------------------------+ 556 | 3 | :attr:`tm_hour` | range [0, 23] | 557 +-------+-------------------+---------------------------------+ 558 | 4 | :attr:`tm_min` | range [0, 59] | 559 +-------+-------------------+---------------------------------+ 560 | 5 | :attr:`tm_sec` | range [0, 61]; see **(2)** in | 561 | | | :func:`strftime` description | 562 +-------+-------------------+---------------------------------+ 563 | 6 | :attr:`tm_wday` | range [0, 6], Monday is 0 | 564 +-------+-------------------+---------------------------------+ 565 | 7 | :attr:`tm_yday` | range [1, 366] | 566 +-------+-------------------+---------------------------------+ 567 | 8 | :attr:`tm_isdst` | 0, 1 or -1; see below | 568 +-------+-------------------+---------------------------------+ 569 | N/A | :attr:`tm_zone` | abbreviation of timezone name | 570 +-------+-------------------+---------------------------------+ 571 | N/A | :attr:`tm_gmtoff` | offset east of UTC in seconds | 572 +-------+-------------------+---------------------------------+ 573 574 Note that unlike the C structure, the month value is a range of [1, 12], not 575 [0, 11]. 576 577 In calls to :func:`mktime`, :attr:`tm_isdst` may be set to 1 when daylight 578 savings time is in effect, and 0 when it is not. A value of -1 indicates that 579 this is not known, and will usually result in the correct state being filled in. 580 581 When a tuple with an incorrect length is passed to a function expecting a 582 :class:`struct_time`, or having elements of the wrong type, a 583 :exc:`TypeError` is raised. 584 585 .. function:: time() 586 587 Return the time in seconds since the epoch_ as a floating point 588 number. The specific date of the epoch and the handling of 589 `leap seconds`_ is platform dependent. 590 On Windows and most Unix systems, the epoch is January 1, 1970, 591 00:00:00 (UTC) and leap seconds are not counted towards the time 592 in seconds since the epoch. This is commonly referred to as 593 `Unix time <https://en.wikipedia.org/wiki/Unix_time>`_. 594 To find out what the epoch is on a given platform, look at 595 ``gmtime(0)``. 596 597 Note that even though the time is always returned as a floating point 598 number, not all systems provide time with a better precision than 1 second. 599 While this function normally returns non-decreasing values, it can return a 600 lower value than a previous call if the system clock has been set back 601 between the two calls. 602 603 The number returned by :func:`.time` may be converted into a more common 604 time format (i.e. year, month, day, hour, etc...) in UTC by passing it to 605 :func:`gmtime` function or in local time by passing it to the 606 :func:`localtime` function. In both cases a 607 :class:`struct_time` object is returned, from which the components 608 of the calendar date may be accessed as attributes. 609 610 .. data:: timezone 611 612 The offset of the local (non-DST) timezone, in seconds west of UTC (negative in 613 most of Western Europe, positive in the US, zero in the UK). 614 615 616 .. data:: tzname 617 618 A tuple of two strings: the first is the name of the local non-DST timezone, the 619 second is the name of the local DST timezone. If no DST timezone is defined, 620 the second string should not be used. 621 622 623 .. function:: tzset() 624 625 Resets the time conversion rules used by the library routines. The environment 626 variable :envvar:`TZ` specifies how this is done. 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 .. seealso:: 707 708 Module :mod:`datetime` 709 More object-oriented interface to dates and times. 710 711 Module :mod:`locale` 712 Internationalization services. The locale setting affects the interpretation 713 of many format specifiers in :func:`strftime` and :func:`strptime`. 714 715 Module :mod:`calendar` 716 General calendar-related functions. :func:`~calendar.timegm` is the 717 inverse of :func:`gmtime` from this module. 718 719 .. rubric:: Footnotes 720 721 .. [#] The use of ``%Z`` is now deprecated, but the ``%z`` escape that expands to the 722 preferred hour/minute offset is not supported by all ANSI C libraries. Also, a 723 strict reading of the original 1982 :rfc:`822` standard calls for a two-digit 724 year (%y rather than %Y), but practice moved to 4-digit years long before the 725 year 2000. After that, :rfc:`822` became obsolete and the 4-digit year has 726 been first recommended by :rfc:`1123` and then mandated by :rfc:`2822`. 727 728
