1 2 :mod:`time` --- Time access and conversions 3 =========================================== 4 5 .. module:: time 6 :synopsis: Time access and conversions. 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 .. index:: single: epoch 21 22 * The :dfn:`epoch` is the point where the time starts. On January 1st of that 23 year, at 0 hours, the "time since the epoch" is zero. For Unix, the epoch is 24 1970. To find out what the epoch is, look at ``gmtime(0)``. 25 26 .. index:: single: Year 2038 27 28 * The functions in this module do not handle dates and times before the epoch or 29 far in the future. The cut-off point in the future is determined by the C 30 library; for Unix, it is typically in 2038. 31 32 .. index:: 33 single: Year 2000 34 single: Y2K 35 36 .. _time-y2kissues: 37 38 * **Year 2000 (Y2K) issues**: Python depends on the platform's C library, which 39 generally doesn't have year 2000 issues, since all dates and times are 40 represented internally as seconds since the epoch. Functions accepting a 41 :class:`struct_time` (see below) generally require a 4-digit year. For backward 42 compatibility, 2-digit years are supported if the module variable 43 ``accept2dyear`` is a non-zero integer; this variable is initialized to ``1`` 44 unless the environment variable :envvar:`PYTHONY2K` is set to a non-empty 45 string, in which case it is initialized to ``0``. Thus, you can set 46 :envvar:`PYTHONY2K` to a non-empty string in the environment to require 4-digit 47 years for all year input. When 2-digit years are accepted, they are converted 48 according to the POSIX or X/Open standard: values 69-99 are mapped to 1969-1999, 49 and values 0--68 are mapped to 2000--2068. Values 100--1899 are always illegal. 50 51 .. index:: 52 single: UTC 53 single: Coordinated Universal Time 54 single: Greenwich Mean Time 55 56 * UTC is Coordinated Universal Time (formerly known as Greenwich Mean Time, or 57 GMT). The acronym UTC is not a mistake but a compromise between English and 58 French. 59 60 .. index:: single: Daylight Saving Time 61 62 * DST is Daylight Saving Time, an adjustment of the timezone by (usually) one 63 hour during part of the year. DST rules are magic (determined by local law) and 64 can change from year to year. The C library has a table containing the local 65 rules (often it is read from a system file for flexibility) and is the only 66 source of True Wisdom in this respect. 67 68 * The precision of the various real-time functions may be less than suggested by 69 the units in which their value or argument is expressed. E.g. on most Unix 70 systems, the clock "ticks" only 50 or 100 times a second. 71 72 * On the other hand, the precision of :func:`.time` and :func:`sleep` is better 73 than their Unix equivalents: times are expressed as floating point numbers, 74 :func:`.time` returns the most accurate time available (using Unix 75 :c:func:`gettimeofday` where available), and :func:`sleep` will accept a time 76 with a nonzero fraction (Unix :c:func:`select` is used to implement this, where 77 available). 78 79 * The time value as returned by :func:`gmtime`, :func:`localtime`, and 80 :func:`strptime`, and accepted by :func:`asctime`, :func:`mktime` and 81 :func:`strftime`, may be considered as a sequence of 9 integers. The return 82 values of :func:`gmtime`, :func:`localtime`, and :func:`strptime` also offer 83 attribute names for individual fields. 84 85 See :class:`struct_time` for a description of these objects. 86 87 .. versionchanged:: 2.2 88 The time value sequence was changed from a tuple to a :class:`struct_time`, with 89 the addition of attribute names for the fields. 90 91 * Use the following functions to convert between time representations: 92 93 +-------------------------+-------------------------+-------------------------+ 94 | From | To | Use | 95 +=========================+=========================+=========================+ 96 | seconds since the epoch | :class:`struct_time` in | :func:`gmtime` | 97 | | UTC | | 98 +-------------------------+-------------------------+-------------------------+ 99 | seconds since the epoch | :class:`struct_time` in | :func:`localtime` | 100 | | local time | | 101 +-------------------------+-------------------------+-------------------------+ 102 | :class:`struct_time` in | seconds since the epoch | :func:`calendar.timegm` | 103 | UTC | | | 104 +-------------------------+-------------------------+-------------------------+ 105 | :class:`struct_time` in | seconds since the epoch | :func:`mktime` | 106 | local time | | | 107 +-------------------------+-------------------------+-------------------------+ 108 109 110 The module defines the following functions and data items: 111 112 .. data:: accept2dyear 113 114 Boolean value indicating whether two-digit year values will be accepted. This 115 is true by default, but will be set to false if the environment variable 116 :envvar:`PYTHONY2K` has been set to a non-empty string. It may also be modified 117 at run time. 118 119 120 .. data:: altzone 121 122 The offset of the local DST timezone, in seconds west of UTC, if one is defined. 123 This is negative if the local DST timezone is east of UTC (as in Western Europe, 124 including the UK). Only use this if ``daylight`` is nonzero. 125 126 127 .. function:: asctime([t]) 128 129 Convert a tuple or :class:`struct_time` representing a time as returned by 130 :func:`gmtime` or :func:`localtime` to a 24-character string of the following 131 form: ``'Sun Jun 20 23:21:05 1993'``. If *t* is not provided, the current time 132 as returned by :func:`localtime` is used. Locale information is not used by 133 :func:`asctime`. 134 135 .. note:: 136 137 Unlike the C function of the same name, there is no trailing newline. 138 139 .. versionchanged:: 2.1 140 Allowed *t* to be omitted. 141 142 143 .. function:: clock() 144 145 .. index:: 146 single: CPU time 147 single: processor time 148 single: benchmarking 149 150 On Unix, return the current processor time as a floating point number expressed 151 in seconds. The precision, and in fact the very definition of the meaning of 152 "processor time", depends on that of the C function of the same name, but in any 153 case, this is the function to use for benchmarking Python or timing algorithms. 154 155 On Windows, this function returns wall-clock seconds elapsed since the first 156 call to this function, as a floating point number, based on the Win32 function 157 :c:func:`QueryPerformanceCounter`. The resolution is typically better than one 158 microsecond. 159 160 161 .. function:: ctime([secs]) 162 163 Convert a time expressed in seconds since the epoch to a string representing 164 local time. If *secs* is not provided or :const:`None`, the current time as 165 returned by :func:`.time` is used. ``ctime(secs)`` is equivalent to 166 ``asctime(localtime(secs))``. Locale information is not used by :func:`ctime`. 167 168 .. versionchanged:: 2.1 169 Allowed *secs* to be omitted. 170 171 .. versionchanged:: 2.4 172 If *secs* is :const:`None`, the current time is used. 173 174 175 .. data:: daylight 176 177 Nonzero if a DST timezone is defined. 178 179 180 .. function:: gmtime([secs]) 181 182 Convert a time expressed in seconds since the epoch to a :class:`struct_time` in 183 UTC in which the dst flag is always zero. If *secs* is not provided or 184 :const:`None`, the current time as returned by :func:`.time` is used. Fractions 185 of a second are ignored. See above for a description of the 186 :class:`struct_time` object. See :func:`calendar.timegm` for the inverse of this 187 function. 188 189 .. versionchanged:: 2.1 190 Allowed *secs* to be omitted. 191 192 .. versionchanged:: 2.4 193 If *secs* is :const:`None`, the current time is used. 194 195 196 .. function:: localtime([secs]) 197 198 Like :func:`gmtime` but converts to local time. If *secs* is not provided or 199 :const:`None`, the current time as returned by :func:`.time` is used. The dst 200 flag is set to ``1`` when DST applies to the given time. 201 202 .. versionchanged:: 2.1 203 Allowed *secs* to be omitted. 204 205 .. versionchanged:: 2.4 206 If *secs* is :const:`None`, the current time is used. 207 208 209 .. function:: mktime(t) 210 211 This is the inverse function of :func:`localtime`. Its argument is the 212 :class:`struct_time` or full 9-tuple (since the dst flag is needed; use ``-1`` 213 as the dst flag if it is unknown) which expresses the time in *local* time, not 214 UTC. It returns a floating point number, for compatibility with :func:`.time`. 215 If the input value cannot be represented as a valid time, either 216 :exc:`OverflowError` or :exc:`ValueError` will be raised (which depends on 217 whether the invalid value is caught by Python or the underlying C libraries). 218 The earliest date for which it can generate a time is platform-dependent. 219 220 221 .. function:: sleep(secs) 222 223 Suspend execution of the current thread for the given number of seconds. 224 The argument may be a floating point number to indicate a more precise sleep 225 time. The actual suspension time may be less than that requested because any 226 caught signal will terminate the :func:`sleep` following execution of that 227 signal's catching routine. Also, the suspension time may be longer than 228 requested by an arbitrary amount because of the scheduling of other activity 229 in the system. 230 231 232 .. function:: strftime(format[, t]) 233 234 Convert a tuple or :class:`struct_time` representing a time as returned by 235 :func:`gmtime` or :func:`localtime` to a string as specified by the *format* 236 argument. If *t* is not provided, the current time as returned by 237 :func:`localtime` is used. *format* must be a string. :exc:`ValueError` is 238 raised if any field in *t* is outside of the allowed range. :func:`strftime` 239 returns a locale dependent byte string; the result may be converted to unicode 240 by doing ``strftime(<myformat>).decode(locale.getlocale()[1])``. 241 242 .. versionchanged:: 2.1 243 Allowed *t* to be omitted. 244 245 .. versionchanged:: 2.4 246 :exc:`ValueError` raised if a field in *t* is out of range. 247 248 .. versionchanged:: 2.5 249 0 is now a legal argument for any position in the time tuple; if it is normally 250 illegal the value is forced to a correct one. 251 252 The following directives can be embedded in the *format* string. They are shown 253 without the optional field width and precision specification, and are replaced 254 by the indicated characters in the :func:`strftime` result: 255 256 +-----------+--------------------------------+-------+ 257 | Directive | Meaning | Notes | 258 +===========+================================+=======+ 259 | ``%a`` | Locale's abbreviated weekday | | 260 | | name. | | 261 +-----------+--------------------------------+-------+ 262 | ``%A`` | Locale's full weekday name. | | 263 +-----------+--------------------------------+-------+ 264 | ``%b`` | Locale's abbreviated month | | 265 | | name. | | 266 +-----------+--------------------------------+-------+ 267 | ``%B`` | Locale's full month name. | | 268 +-----------+--------------------------------+-------+ 269 | ``%c`` | Locale's appropriate date and | | 270 | | time representation. | | 271 +-----------+--------------------------------+-------+ 272 | ``%d`` | Day of the month as a decimal | | 273 | | number [01,31]. | | 274 +-----------+--------------------------------+-------+ 275 | ``%H`` | Hour (24-hour clock) as a | | 276 | | decimal number [00,23]. | | 277 +-----------+--------------------------------+-------+ 278 | ``%I`` | Hour (12-hour clock) as a | | 279 | | decimal number [01,12]. | | 280 +-----------+--------------------------------+-------+ 281 | ``%j`` | Day of the year as a decimal | | 282 | | number [001,366]. | | 283 +-----------+--------------------------------+-------+ 284 | ``%m`` | Month as a decimal number | | 285 | | [01,12]. | | 286 +-----------+--------------------------------+-------+ 287 | ``%M`` | Minute as a decimal number | | 288 | | [00,59]. | | 289 +-----------+--------------------------------+-------+ 290 | ``%p`` | Locale's equivalent of either | \(1) | 291 | | AM or PM. | | 292 +-----------+--------------------------------+-------+ 293 | ``%S`` | Second as a decimal number | \(2) | 294 | | [00,61]. | | 295 +-----------+--------------------------------+-------+ 296 | ``%U`` | Week number of the year | \(3) | 297 | | (Sunday as the first day of | | 298 | | the week) as a decimal number | | 299 | | [00,53]. All days in a new | | 300 | | year preceding the first | | 301 | | Sunday are considered to be in | | 302 | | week 0. | | 303 +-----------+--------------------------------+-------+ 304 | ``%w`` | Weekday as a decimal number | | 305 | | [0(Sunday),6]. | | 306 +-----------+--------------------------------+-------+ 307 | ``%W`` | Week number of the year | \(3) | 308 | | (Monday as the first day of | | 309 | | the week) as a decimal number | | 310 | | [00,53]. All days in a new | | 311 | | year preceding the first | | 312 | | Monday are considered to be in | | 313 | | week 0. | | 314 +-----------+--------------------------------+-------+ 315 | ``%x`` | Locale's appropriate date | | 316 | | representation. | | 317 +-----------+--------------------------------+-------+ 318 | ``%X`` | Locale's appropriate time | | 319 | | representation. | | 320 +-----------+--------------------------------+-------+ 321 | ``%y`` | Year without century as a | | 322 | | decimal number [00,99]. | | 323 +-----------+--------------------------------+-------+ 324 | ``%Y`` | Year with century as a decimal | | 325 | | number. | | 326 +-----------+--------------------------------+-------+ 327 | ``%Z`` | Time zone name (no characters | | 328 | | if no time zone exists). | | 329 +-----------+--------------------------------+-------+ 330 | ``%%`` | A literal ``'%'`` character. | | 331 +-----------+--------------------------------+-------+ 332 333 Notes: 334 335 (1) 336 When used with the :func:`strptime` function, the ``%p`` directive only affects 337 the output hour field if the ``%I`` directive is used to parse the hour. 338 339 (2) 340 The range really is ``0`` to ``61``; this accounts for leap seconds and the 341 (very rare) double leap seconds. 342 343 (3) 344 When used with the :func:`strptime` function, ``%U`` and ``%W`` are only used in 345 calculations when the day of the week and the year are specified. 346 347 Here is an example, a format for dates compatible with that specified in the 348 :rfc:`2822` Internet email standard. [#]_ :: 349 350 >>> from time import gmtime, strftime 351 >>> strftime("%a, %d %b %Y %H:%M:%S +0000", gmtime()) 352 'Thu, 28 Jun 2001 14:17:15 +0000' 353 354 Additional directives may be supported on certain platforms, but only the 355 ones listed here have a meaning standardized by ANSI C. To see the full set 356 of format codes supported on your platform, consult the :manpage:`strftime(3)` 357 documentation. 358 359 On some platforms, an optional field width and precision specification can 360 immediately follow the initial ``'%'`` of a directive in the following order; 361 this is also not portable. The field width is normally 2 except for ``%j`` where 362 it is 3. 363 364 365 .. function:: strptime(string[, format]) 366 367 Parse a string representing a time according to a format. The return value is 368 a :class:`struct_time` as returned by :func:`gmtime` or :func:`localtime`. 369 370 The *format* parameter uses the same directives as those used by 371 :func:`strftime`; it defaults to ``"%a %b %d %H:%M:%S %Y"`` which matches the 372 formatting returned by :func:`ctime`. If *string* cannot be parsed according to 373 *format*, or if it has excess data after parsing, :exc:`ValueError` is raised. 374 The default values used to fill in any missing data when more accurate values 375 cannot be inferred are ``(1900, 1, 1, 0, 0, 0, 0, 1, -1)``. 376 377 For example: 378 379 >>> import time 380 >>> time.strptime("30 Nov 00", "%d %b %y") # doctest: +NORMALIZE_WHITESPACE 381 time.struct_time(tm_year=2000, tm_mon=11, tm_mday=30, tm_hour=0, tm_min=0, 382 tm_sec=0, tm_wday=3, tm_yday=335, tm_isdst=-1) 383 384 Support for the ``%Z`` directive is based on the values contained in ``tzname`` 385 and whether ``daylight`` is true. Because of this, it is platform-specific 386 except for recognizing UTC and GMT which are always known (and are considered to 387 be non-daylight savings timezones). 388 389 Only the directives specified in the documentation are supported. Because 390 ``strftime()`` is implemented per platform it can sometimes offer more 391 directives than those listed. But ``strptime()`` is independent of any platform 392 and thus does not necessarily support all directives available that are not 393 documented as supported. 394 395 396 .. class:: struct_time 397 398 The type of the time value sequence returned by :func:`gmtime`, 399 :func:`localtime`, and :func:`strptime`. It is an object with a :term:`named 400 tuple` interface: values can be accessed by index and by attribute name. The 401 following values are present: 402 403 +-------+-------------------+---------------------------------+ 404 | Index | Attribute | Values | 405 +=======+===================+=================================+ 406 | 0 | :attr:`tm_year` | (for example, 1993) | 407 +-------+-------------------+---------------------------------+ 408 | 1 | :attr:`tm_mon` | range [1, 12] | 409 +-------+-------------------+---------------------------------+ 410 | 2 | :attr:`tm_mday` | range [1, 31] | 411 +-------+-------------------+---------------------------------+ 412 | 3 | :attr:`tm_hour` | range [0, 23] | 413 +-------+-------------------+---------------------------------+ 414 | 4 | :attr:`tm_min` | range [0, 59] | 415 +-------+-------------------+---------------------------------+ 416 | 5 | :attr:`tm_sec` | range [0, 61]; see **(2)** in | 417 | | | :func:`strftime` description | 418 +-------+-------------------+---------------------------------+ 419 | 6 | :attr:`tm_wday` | range [0, 6], Monday is 0 | 420 +-------+-------------------+---------------------------------+ 421 | 7 | :attr:`tm_yday` | range [1, 366] | 422 +-------+-------------------+---------------------------------+ 423 | 8 | :attr:`tm_isdst` | 0, 1 or -1; see below | 424 +-------+-------------------+---------------------------------+ 425 426 .. versionadded:: 2.2 427 428 Note that unlike the C structure, the month value is a range of [1, 12], not 429 [0, 11]. A year value will be handled as described under :ref:`Year 2000 430 (Y2K) issues <time-y2kissues>` above. 431 432 In calls to :func:`mktime`, :attr:`tm_isdst` may be set to 1 when daylight 433 savings time is in effect, and 0 when it is not. A value of -1 indicates 434 that this is not known, and will usually result in the correct state being 435 filled in. 436 437 When a tuple with an incorrect length is passed to a function expecting a 438 :class:`struct_time`, or having elements of the wrong type, a 439 :exc:`TypeError` is raised. 440 441 442 .. function:: time() 443 444 Return the time in seconds since the epoch as a floating point number. 445 Note that even though the time is always returned as a floating point 446 number, not all systems provide time with a better precision than 1 second. 447 While this function normally returns non-decreasing values, it can return a 448 lower value than a previous call if the system clock has been set back between 449 the two calls. 450 451 452 .. data:: timezone 453 454 The offset of the local (non-DST) timezone, in seconds west of UTC (negative in 455 most of Western Europe, positive in the US, zero in the UK). 456 457 458 .. data:: tzname 459 460 A tuple of two strings: the first is the name of the local non-DST timezone, the 461 second is the name of the local DST timezone. If no DST timezone is defined, 462 the second string should not be used. 463 464 465 .. function:: tzset() 466 467 Reset the time conversion rules used by the library routines. The environment 468 variable :envvar:`TZ` specifies how this is done. It will also set the variables 469 ``tzname`` (from the :envvar:`TZ` environment variable), ``timezone`` (non-DST 470 seconds West of UTC), ``altzone`` (DST seconds west of UTC) and ``daylight`` 471 (to 0 if this timezone does not have any daylight saving time rules, or to 472 nonzero if there is a time, past, present or future when daylight saving time 473 applies). 474 475 .. versionadded:: 2.3 476 477 Availability: Unix. 478 479 .. note:: 480 481 Although in many cases, changing the :envvar:`TZ` environment variable may 482 affect the output of functions like :func:`localtime` without calling 483 :func:`tzset`, this behavior should not be relied on. 484 485 The :envvar:`TZ` environment variable should contain no whitespace. 486 487 The standard format of the :envvar:`TZ` environment variable is (whitespace 488 added for clarity):: 489 490 std offset [dst [offset [,start[/time], end[/time]]]] 491 492 Where the components are: 493 494 ``std`` and ``dst`` 495 Three or more alphanumerics giving the timezone abbreviations. These will be 496 propagated into time.tzname 497 498 ``offset`` 499 The offset has the form: `` hh[:mm[:ss]]``. This indicates the value 500 added the local time to arrive at UTC. If preceded by a '-', the timezone 501 is east of the Prime Meridian; otherwise, it is west. If no offset follows 502 dst, summer time is assumed to be one hour ahead of standard time. 503 504 ``start[/time], end[/time]`` 505 Indicates when to change to and back from DST. The format of the 506 start and end dates are one of the following: 507 508 :samp:`J{n}` 509 The Julian day *n* (1 <= *n* <= 365). Leap days are not counted, so in 510 all years February 28 is day 59 and March 1 is day 60. 511 512 :samp:`{n}` 513 The zero-based Julian day (0 <= *n* <= 365). Leap days are counted, and 514 it is possible to refer to February 29. 515 516 :samp:`M{m}.{n}.{d}` 517 The *d*'th day (0 <= *d* <= 6) or week *n* of month *m* of the year (1 518 <= *n* <= 5, 1 <= *m* <= 12, where week 5 means "the last *d* day in 519 month *m*" which may occur in either the fourth or the fifth 520 week). Week 1 is the first week in which the *d*'th day occurs. Day 521 zero is Sunday. 522 523 ``time`` has the same format as ``offset`` except that no leading sign 524 ('-' or '+') is allowed. The default, if time is not given, is 02:00:00. 525 526 :: 527 528 >>> os.environ['TZ'] = 'EST+05EDT,M4.1.0,M10.5.0' 529 >>> time.tzset() 530 >>> time.strftime('%X %x %Z') 531 '02:07:36 05/08/03 EDT' 532 >>> os.environ['TZ'] = 'AEST-10AEDT-11,M10.5.0,M3.5.0' 533 >>> time.tzset() 534 >>> time.strftime('%X %x %Z') 535 '16:08:12 05/08/03 AEST' 536 537 On many Unix systems (including \*BSD, Linux, Solaris, and Darwin), it is more 538 convenient to use the system's zoneinfo (:manpage:`tzfile(5)`) database to 539 specify the timezone rules. To do this, set the :envvar:`TZ` environment 540 variable to the path of the required timezone datafile, relative to the root of 541 the systems 'zoneinfo' timezone database, usually located at 542 :file:`/usr/share/zoneinfo`. For example, ``'US/Eastern'``, 543 ``'Australia/Melbourne'``, ``'Egypt'`` or ``'Europe/Amsterdam'``. :: 544 545 >>> os.environ['TZ'] = 'US/Eastern' 546 >>> time.tzset() 547 >>> time.tzname 548 ('EST', 'EDT') 549 >>> os.environ['TZ'] = 'Egypt' 550 >>> time.tzset() 551 >>> time.tzname 552 ('EET', 'EEST') 553 554 555 .. seealso:: 556 557 Module :mod:`datetime` 558 More object-oriented interface to dates and times. 559 560 Module :mod:`locale` 561 Internationalization services. The locale setting affects the interpretation 562 of many format specifiers in :func:`strftime` and :func:`strptime`. 563 564 Module :mod:`calendar` 565 General calendar-related functions. :func:`~calendar.timegm` is the 566 inverse of :func:`gmtime` from this module. 567 568 .. rubric:: Footnotes 569 570 .. [#] The use of ``%Z`` is now deprecated, but the ``%z`` escape that expands to the 571 preferred hour/minute offset is not supported by all ANSI C libraries. Also, a 572 strict reading of the original 1982 :rfc:`822` standard calls for a two-digit 573 year (%y rather than %Y), but practice moved to 4-digit years long before the 574 year 2000. After that, :rfc:`822` became obsolete and the 4-digit year has 575 been first recommended by :rfc:`1123` and then mandated by :rfc:`2822`. 576 577
