time— Time access and conversions

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This module provides various time-related functions. For related functionality, see also thedatetimeandcalendarmodules.

Although this module is always available, not all functions are available on all platforms. Most of the functions defined in this module call platform C library functions with the same name. It may sometimes be helpful to consult the platform documentation, because the semantics of these functions varies among platforms.

An explanation of some terminology and conventions is in order.

• Theepochis the point where the time starts, the return value of time.gmtime(0).It is January 1, 1970, 00:00:00 (UTC) on all platforms.

• The termseconds since the epochrefers to the total number of elapsed seconds since the epoch, typically excluding leap seconds.Leap seconds are excluded from this total on all POSIX-compliant platforms.

• The functions in this module may not handle dates and times before theepochor far in the future. The cut-off point in the future is determined by the C library; for 32-bit systems, it is typically in 2038.

• Functionstrptime()can parse 2-digit years when given%yformat code. When 2-digit years are parsed, they are converted according to the POSIX and ISO C standards: values 69–99 are mapped to 1969–1999, and values 0–68 are mapped to 2000–2068.

• UTC is Coordinated Universal Time (formerly known as Greenwich Mean Time, or GMT). The acronym UTC is not a mistake but a compromise between English and French.

• DST is Daylight Saving Time, an adjustment of the timezone by (usually) one hour during part of the year. DST rules are magic (determined by local law) and can change from year to year. The C library has a table containing the local rules (often it is read from a system file for flexibility) and is the only source of True Wisdom in this respect.

• The precision of the various real-time functions may be less than suggested by the units in which their value or argument is expressed. E.g. on most Unix systems, the clock “ticks” only 50 or 100 times a second.

• On the other hand, the precision oftime()andsleep()is better than their Unix equivalents: times are expressed as floating-point numbers, time()returns the most accurate time available (using Unix gettimeofday()where available), andsleep()will accept a time with a nonzero fraction (Unixselect()is used to implement this, where available).

• The time value as returned bygmtime(),localtime(),and strptime(),and accepted byasctime(),mktime()and strftime(),is a sequence of 9 integers. The return values of gmtime(),localtime(),andstrptime()also offer attribute names for individual fields.

  Seestruct_timefor a description of these objects.

  Changed in version 3.3:Thestruct_timetype was extended to provide thetm_gmtoffandtm_zone attributes when platform supports corresponding structtmmembers.

  Changed in version 3.6:Thestruct_timeattributes tm_gmtoffandtm_zone are now available on all platforms.

• Use the following functions to convert between time representations:

  From	To	Use
  seconds since the epoch	struct_timein UTC	gmtime()
  seconds since the epoch	struct_timein local time	localtime()
  struct_timein UTC	seconds since the epoch	calendar.timegm()
  struct_timein local time	seconds since the epoch	mktime()

Functions

time.asctime([t])

Convert a tuple orstruct_timerepresenting a time as returned by gmtime()orlocaltime()to a string of the following form:'SunJun2023:21:051993'.The day field is two characters long and is space padded if the day is a single digit, e.g.:'WedJun904:26:401993'.

Iftis not provided, the current time as returned bylocaltime() is used. Locale information is not used byasctime().

Note

Unlike the C function of the same name,asctime()does not add a trailing newline.

time.pthread_getcpuclockid(thread_id)

Return theclk_idof the thread-specific CPU-time clock for the specifiedthread_id.

Usethreading.get_ident()or theident attribute ofthreading.Threadobjects to get a suitable value forthread_id.

Warning

Passing an invalid or expiredthread_idmay result in undefined behavior, such as segmentation fault.

Availability:Unix

See the man page forpthread_getcpuclockid(3)for further information.

Added in version 3.7.

time.clock_getres(clk_id)

Return the resolution (precision) of the specified clockclk_id.Refer to Clock ID Constantsfor a list of accepted values forclk_id.

Availability:Unix.

Added in version 3.3.

time.clock_gettime(clk_id)→float

Return the time of the specified clockclk_id.Refer to Clock ID Constantsfor a list of accepted values forclk_id.

Useclock_gettime_ns()to avoid the precision loss caused by the floattype.

Availability:Unix.

Added in version 3.3.

time.clock_gettime_ns(clk_id)→int

Similar toclock_gettime()but return time as nanoseconds.

Availability:Unix.

Added in version 3.7.

time.clock_settime(clk_id,time:float)

Set the time of the specified clockclk_id.Currently, CLOCK_REALTIMEis the only accepted value forclk_id.

Useclock_settime_ns()to avoid the precision loss caused by the floattype.

Availability:Unix, not Android, not iOS.

Added in version 3.3.

time.clock_settime_ns(clk_id,time:int)

Similar toclock_settime()but set time with nanoseconds.

Availability:Unix, not Android, not iOS.

Added in version 3.7.

time.ctime([secs])

Convert a time expressed in seconds since theepochto a string of a form: 'SunJun2023:21:051993'representing local time. The day field is two characters long and is space padded if the day is a single digit, e.g.:'WedJun904:26:401993'.

Ifsecsis not provided orNone,the current time as returned bytime()is used.ctime(secs)is equivalent to asctime(localtime(secs)).Locale information is not used by ctime().

time.get_clock_info(name)

Get information on the specified clock as a namespace object. Supported clock names and the corresponding functions to read their value are:

• 'monotonic':time.monotonic()

• 'perf_counter':time.perf_counter()

• 'process_time':time.process_time()

• 'thread_time':time.thread_time()

• 'time':time.time()

The result has the following attributes:

• adjustable:Trueif the clock can be changed automatically (e.g. by a NTP daemon) or manually by the system administrator,Falseotherwise

• implementation:The name of the underlying C function used to get the clock value. Refer toClock ID Constantsfor possible values.

• monotonic:Trueif the clock cannot go backward, Falseotherwise

• resolution:The resolution of the clock in seconds (float)

Added in version 3.3.

time.gmtime([secs])

Convert a time expressed in seconds since theepochto astruct_timein UTC in which the dst flag is always zero. Ifsecsis not provided or None,the current time as returned bytime()is used. Fractions of a second are ignored. See above for a description of the struct_timeobject. Seecalendar.timegm()for the inverse of this function.

time.localtime([secs])

Likegmtime()but converts to local time. Ifsecsis not provided or None,the current time as returned bytime()is used. The dst flag is set to1when DST applies to the given time.

localtime()may raiseOverflowError,if the timestamp is outside the range of values supported by the platform Clocaltime() orgmtime()functions, andOSErroronlocaltime()or gmtime()failure. It’s common for this to be restricted to years between 1970 and 2038.

time.mktime(t)

This is the inverse function oflocaltime().Its argument is the struct_timeor full 9-tuple (since the dst flag is needed; use-1 as the dst flag if it is unknown) which expresses the time inlocaltime, not UTC. It returns a floating-point number, for compatibility withtime(). If the input value cannot be represented as a valid time, either OverflowErrororValueErrorwill be raised (which depends on whether the invalid value is caught by Python or the underlying C libraries). The earliest date for which it can generate a time is platform-dependent.

time.monotonic()→float

Return the value (in fractional seconds) of a monotonic clock, i.e. a clock that cannot go backwards. The clock is not affected by system clock updates. The reference point of the returned value is undefined, so that only the difference between the results of two calls is valid.

Clock:

• On Windows, callQueryPerformanceCounter()and QueryPerformanceFrequency().

• On macOS, callmach_absolute_time()andmach_timebase_info().

• On HP-UX, callgethrtime().

• Callclock_gettime(CLOCK_HIGHRES)if available.

• Otherwise, callclock_gettime(CLOCK_MONOTONIC).

Usemonotonic_ns()to avoid the precision loss caused by the floattype.

Added in version 3.3.

Changed in version 3.5:The function is now always available and always system-wide.

Changed in version 3.10:On macOS, the function is now system-wide.

time.monotonic_ns()→int

Similar tomonotonic(),but return time as nanoseconds.

Added in version 3.7.

time.perf_counter()→float

Return the value (in fractional seconds) of a performance counter, i.e. a clock with the highest available resolution to measure a short duration. It does include time elapsed during sleep and is system-wide. The reference point of the returned value is undefined, so that only the difference between the results of two calls is valid.

CPython implementation detail:On CPython, use the same clock astime.monotonic()and is a monotonic clock, i.e. a clock that cannot go backwards.

Useperf_counter_ns()to avoid the precision loss caused by the floattype.

Added in version 3.3.

Changed in version 3.10:On Windows, the function is now system-wide.

Changed in version 3.13:Use the same clock astime.monotonic().

time.perf_counter_ns()→int

Similar toperf_counter(),but return time as nanoseconds.

Added in version 3.7.

time.process_time()→float

Return the value (in fractional seconds) of the sum of the system and user CPU time of the current process. It does not include time elapsed during sleep. It is process-wide by definition. The reference point of the returned value is undefined, so that only the difference between the results of two calls is valid.

Useprocess_time_ns()to avoid the precision loss caused by the floattype.

Added in version 3.3.

time.process_time_ns()→int

Similar toprocess_time()but return time as nanoseconds.

Added in version 3.7.

time.sleep(secs)

Suspend execution of the calling thread for the given number of seconds. The argument may be a floating-point number to indicate a more precise sleep time.

If the sleep is interrupted by a signal and no exception is raised by the signal handler, the sleep is restarted with a recomputed timeout.

The suspension time may be longer than requested by an arbitrary amount, because of the scheduling of other activity in the system.

On Windows, ifsecsis zero, the thread relinquishes the remainder of its time slice to any other thread that is ready to run. If there are no other threads ready to run, the function returns immediately, and the thread continues execution. On Windows 8.1 and newer the implementation uses ahigh-resolution timer which provides resolution of 100 nanoseconds. Ifsecsis zero,Sleep(0)is used.

Unix implementation:

• Useclock_nanosleep()if available (resolution: 1 nanosecond);

• Or usenanosleep()if available (resolution: 1 nanosecond);

• Or useselect()(resolution: 1 microsecond).

Raises anauditing eventtime.sleepwith argumentsecs.

Changed in version 3.5:The function now sleeps at leastsecseven if the sleep is interrupted by a signal, except if the signal handler raises an exception (see PEP 475for the rationale).

Changed in version 3.11:On Unix, theclock_nanosleep()andnanosleep()functions are now used if available. On Windows, a waitable timer is now used.

Changed in version 3.13:Raises an auditing event.

time.strftime(format[,t])

Convert a tuple orstruct_timerepresenting a time as returned by gmtime()orlocaltime()to a string as specified by theformat argument. Iftis not provided, the current time as returned by localtime()is used.formatmust be a string.ValueErroris raised if any field intis outside of the allowed range.

0 is a legal argument for any position in the time tuple; if it is normally illegal the value is forced to a correct one.

The following directives can be embedded in theformatstring. They are shown without the optional field width and precision specification, and are replaced by the indicated characters in thestrftime()result:

Directive	Meaning	Notes
%a	Locale’s abbreviated weekday name.
%A	Locale’s full weekday name.
%b	Locale’s abbreviated month name.
%B	Locale’s full month name.
%c	Locale’s appropriate date and time representation.
%d	Day of the month as a decimal number [01,31].
%f	Microseconds as a decimal number [000000,999999].	(1)
%H	Hour (24-hour clock) as a decimal number [00,23].
%I	Hour (12-hour clock) as a decimal number [01,12].
%j	Day of the year as a decimal number [001,366].
%m	Month as a decimal number [01,12].
%M	Minute as a decimal number [00,59].
%p	Locale’s equivalent of either AM or PM.	(2)
%S	Second as a decimal number [00,61].	(3)
%U	Week number of the year (Sunday as the first day of the week) as a decimal number [00,53]. All days in a new year preceding the first Sunday are considered to be in week 0.	(4)
%u	Day of the week (Monday is 1; Sunday is 7) as a decimal number [1, 7].
%w	Weekday as a decimal number [0(Sunday),6].
%W	Week number of the year (Monday as the first day of the week) as a decimal number [00,53]. All days in a new year preceding the first Monday are considered to be in week 0.	(4)
%x	Locale’s appropriate date representation.
%X	Locale’s appropriate time representation.
%y	Year without century as a decimal number [00,99].
%Y	Year with century as a decimal number.
%z	Time zone offset indicating a positive or negative time difference from UTC/GMT of the form +HHMM or -HHMM, where H represents decimal hour digits and M represents decimal minute digits [-23:59, +23:59].[1]
%Z	Time zone name (no characters if no time zone exists). Deprecated.[1]
%G	ISO 8601 year (similar to%Ybut follows the rules for the ISO 8601 calendar year). The year starts with the week that contains the first Thursday of the calendar year.
%V	ISO 8601 week number (as a decimal number [01,53]). The first week of the year is the one that contains the first Thursday of the year. Weeks start on Monday.
%%	A literal'%'character.

Notes:

1. The%fformat directive only applies tostrptime(), not tostrftime().However, see alsodatetime.datetime.strptime()and datetime.datetime.strftime()where the%fformat directive applies to microseconds.

2. When used with thestrptime()function, the%pdirective only affects the output hour field if the%Idirective is used to parse the hour.

3. The range really is0to61;value60is valid in timestamps representingleap secondsand value61is supported for historical reasons.

4. When used with thestrptime()function,%Uand%Ware only used in calculations when the day of the week and the year are specified.

Here is an example, a format for dates compatible with that specified in the RFC 2822Internet email standard.[1]

>>>fromtimeimportgmtime,strftime
>>>strftime("%a,%d%b %Y %H:%M:%S +0000 ",gmtime())
'Thu, 28 Jun 2001 14:17:15 +0000'

Additional directives may be supported on certain platforms, but only the ones listed here have a meaning standardized by ANSI C. To see the full set of format codes supported on your platform, consult thestrftime(3) documentation.

On some platforms, an optional field width and precision specification can immediately follow the initial'%'of a directive in the following order; this is also not portable. The field width is normally 2 except for%jwhere it is 3.

time.strptime(string[,format])

Parse a string representing a time according to a format. The return value is astruct_timeas returned bygmtime()or localtime().

Theformatparameter uses the same directives as those used by strftime();it defaults to"%a%b%d%H:%M:%S%Y "which matches the formatting returned byctime().Ifstringcannot be parsed according toformat,or if it has excess data after parsing,ValueErroris raised. The default values used to fill in any missing data when more accurate values cannot be inferred are(1900,1,1,0,0,0,0,1,-1). Bothstringandformatmust be strings.

For example:

>>>importtime
>>>time.strptime("30 Nov 00","%d%b %y ")
time.struct_time(tm_year=2000, tm_mon=11, tm_mday=30, tm_hour=0, tm_min=0,
tm_sec=0, tm_wday=3, tm_yday=335, tm_isdst=-1)

Support for the%Zdirective is based on the values contained intzname and whetherdaylightis true. Because of this, it is platform-specific except for recognizing UTC and GMT which are always known (and are considered to be non-daylight savings timezones).

Only the directives specified in the documentation are supported. Because strftime()is implemented per platform it can sometimes offer more directives than those listed. Butstrptime()is independent of any platform and thus does not necessarily support all directives available that are not documented as supported.

classtime.struct_time

The type of the time value sequence returned bygmtime(), localtime(),andstrptime().It is an object with anamed tupleinterface: values can be accessed by index and by attribute name. The following values are present:

Index	Attribute	Values
0	tm_year	(for example, 1993)
1	tm_mon	range [1, 12]
2	tm_mday	range [1, 31]
3	tm_hour	range [0, 23]
4	tm_min	range [0, 59]
5	tm_sec	range [0, 61]; seeNote (2)instrftime()
6	tm_wday	range [0, 6]; Monday is 0
7	tm_yday	range [1, 366]
8	tm_isdst	0, 1 or -1; see below
N/A	tm_zone	abbreviation of timezone name
N/A	tm_gmtoff	offset east of UTC in seconds

Note that unlike the C structure, the month value is a range of [1, 12], not [0, 11].

In calls tomktime(),tm_isdstmay be set to 1 when daylight savings time is in effect, and 0 when it is not. A value of -1 indicates that this is not known, and will usually result in the correct state being filled in.

When a tuple with an incorrect length is passed to a function expecting a struct_time,or having elements of the wrong type, a TypeErroris raised.

time.time()→float

Return the time in seconds since theepochas a floating-point number. The handling ofleap secondsis platform dependent. On Windows and most Unix systems, the leap seconds are not counted towards the time in seconds since theepoch.This is commonly referred to asUnix time.

Note that even though the time is always returned as a floating-point number, not all systems provide time with a better precision than 1 second. While this function normally returns non-decreasing values, it can return a lower value than a previous call if the system clock has been set back between the two calls.

The number returned bytime()may be converted into a more common time format (i.e. year, month, day, hour, etc…) in UTC by passing it to gmtime()function or in local time by passing it to the localtime()function. In both cases a struct_timeobject is returned, from which the components of the calendar date may be accessed as attributes.

Clock:

• On Windows, callGetSystemTimeAsFileTime().

• Callclock_gettime(CLOCK_REALTIME)if available.

• Otherwise, callgettimeofday().

Usetime_ns()to avoid the precision loss caused by thefloat type.

time.time_ns()→int

Similar totime()but returns time as an integer number of nanoseconds since theepoch.

Added in version 3.7.

time.thread_time()→float

Return the value (in fractional seconds) of the sum of the system and user CPU time of the current thread. It does not include time elapsed during sleep. It is thread-specific by definition. The reference point of the returned value is undefined, so that only the difference between the results of two calls in the same thread is valid.

Usethread_time_ns()to avoid the precision loss caused by the floattype.

Availability:Linux, Unix, Windows.

Unix systems supportingCLOCK_THREAD_CPUTIME_ID.

Added in version 3.7.

time.thread_time_ns()→int

Similar tothread_time()but return time as nanoseconds.

Added in version 3.7.

time.tzset()

Reset the time conversion rules used by the library routines. The environment variableTZspecifies how this is done. It will also set the variables tzname(from theTZenvironment variable),timezone(non-DST seconds West of UTC),altzone(DST seconds west of UTC) anddaylight (to 0 if this timezone does not have any daylight saving time rules, or to nonzero if there is a time, past, present or future when daylight saving time applies).

Availability:Unix.

Note

Although in many cases, changing theTZenvironment variable may affect the output of functions likelocaltime()without calling tzset(),this behavior should not be relied on.

TheTZenvironment variable should contain no whitespace.

The standard format of theTZenvironment variable is (whitespace added for clarity):

stdoffset[dst[offset[,start[/time],end[/time]]]]

Where the components are:

stdanddst

Three or more alphanumerics giving the timezone abbreviations. These will be propagated into time.tzname

offset

The offset has the form:±hh[:mm[:ss]].This indicates the value added the local time to arrive at UTC. If preceded by a ‘-’, the timezone is east of the Prime Meridian; otherwise, it is west. If no offset follows dst, summer time is assumed to be one hour ahead of standard time.

start[/time],end[/time]

Indicates when to change to and back from DST. The format of the start and end dates are one of the following:

Jn

The Julian dayn(1 <=n<= 365). Leap days are not counted, so in all years February 28 is day 59 and March 1 is day 60.

n

The zero-based Julian day (0 <=n<= 365). Leap days are counted, and it is possible to refer to February 29.

Mm.n.d

Thed’th day (0 <=d<= 6) of weeknof monthmof the year (1 <=n<= 5, 1 <=m<= 12, where week 5 means “the lastdday in monthm”which may occur in either the fourth or the fifth week). Week 1 is the first week in which thed’th day occurs. Day zero is a Sunday.

timehas the same format asoffsetexcept that no leading sign (‘-’ or ‘+’) is allowed. The default, if time is not given, is 02:00:00.

>>>os.environ['TZ']='EST+05EDT,M4.1.0,M10.5.0'
>>>time.tzset()
>>>time.strftime('%X%x%Z')
'02:07:36 05/08/03 EDT'
>>>os.environ['TZ']='AEST-10AEDT-11,M10.5.0,M3.5.0'
>>>time.tzset()
>>>time.strftime('%X%x%Z')
'16:08:12 05/08/03 AEST'

On many Unix systems (including *BSD, Linux, Solaris, and Darwin), it is more convenient to use the system’s zoneinfo (tzfile(5)) database to specify the timezone rules. To do this, set theTZenvironment variable to the path of the required timezone datafile, relative to the root of the systems ‘zoneinfo’ timezone database, usually located at /usr/share/zoneinfo.For example,'US/Eastern', 'Australia/Melbourne','Egypt'or'Europe/Amsterdam'.

>>>os.environ['TZ']='US/Eastern'
>>>time.tzset()
>>>time.tzname
('EST', 'EDT')
>>>os.environ['TZ']='Egypt'
>>>time.tzset()
>>>time.tzname
('EET', 'EEST')

Clock ID Constants

These constants are used as parameters forclock_getres()and clock_gettime().

time.CLOCK_BOOTTIME

Identical toCLOCK_MONOTONIC,except it also includes any time that the system is suspended.

This allows applications to get a suspend-aware monotonic clock without having to deal with the complications ofCLOCK_REALTIME,which may have discontinuities if the time is changed usingsettimeofday()or similar.

Availability:Linux >= 2.6.39.

Added in version 3.7.

time.CLOCK_HIGHRES

The Solaris OS has aCLOCK_HIGHREStimer that attempts to use an optimal hardware source, and may give close to nanosecond resolution. CLOCK_HIGHRESis the nonadjustable, high-resolution clock.

Availability:Solaris.

Added in version 3.3.

time.CLOCK_MONOTONIC

Clock that cannot be set and represents monotonic time since some unspecified starting point.

Availability:Unix.

Added in version 3.3.

time.CLOCK_MONOTONIC_RAW

Similar toCLOCK_MONOTONIC,but provides access to a raw hardware-based time that is not subject to NTP adjustments.

Availability:Linux >= 2.6.28, macOS >= 10.12.

Added in version 3.3.

time.CLOCK_MONOTONIC_RAW_APPROX

Similar toCLOCK_MONOTONIC_RAW,but reads a value cached by the system at context switch and hence has less accuracy.

Availability:macOS >= 10.12.

Added in version 3.13.

time.CLOCK_PROCESS_CPUTIME_ID

High-resolution per-process timer from the CPU.

Availability:Unix.

Added in version 3.3.

time.CLOCK_PROF

High-resolution per-process timer from the CPU.

Availability:FreeBSD, NetBSD >= 7, OpenBSD.

Added in version 3.7.

time.CLOCK_TAI

International Atomic Time

The system must have a current leap second table in order for this to give the correct answer. PTP or NTP software can maintain a leap second table.

Availability:Linux.

Added in version 3.9.

time.CLOCK_THREAD_CPUTIME_ID

Thread-specific CPU-time clock.

Availability:Unix.

Added in version 3.3.

time.CLOCK_UPTIME

Time whose absolute value is the time the system has been running and not suspended, providing accurate uptime measurement, both absolute and interval.

Availability:FreeBSD, OpenBSD >= 5.5.

Added in version 3.7.

time.CLOCK_UPTIME_RAW

Clock that increments monotonically, tracking the time since an arbitrary point, unaffected by frequency or time adjustments and not incremented while the system is asleep.

Availability:macOS >= 10.12.

Added in version 3.8.

time.CLOCK_UPTIME_RAW_APPROX

LikeCLOCK_UPTIME_RAW,but the value is cached by the system at context switches and therefore has less accuracy.

Availability:macOS >= 10.12.

Added in version 3.13.

The following constant is the only parameter that can be sent to clock_settime().

time.CLOCK_REALTIME

System-wide real-time clock. Setting this clock requires appropriate privileges.

Availability:Unix.

Added in version 3.3.

Timezone Constants

time.altzone

The offset of the local DST timezone, in seconds west of UTC, if one is defined. This is negative if the local DST timezone is east of UTC (as in Western Europe, including the UK). Only use this ifdaylightis nonzero. See note below.

time.daylight

Nonzero if a DST timezone is defined. See note below.

time.timezone

The offset of the local (non-DST) timezone, in seconds west of UTC (negative in most of Western Europe, positive in the US, zero in the UK). See note below.

time.tzname

A tuple of two strings: the first is the name of the local non-DST timezone, the second is the name of the local DST timezone. If no DST timezone is defined, the second string should not be used. See note below.

Note

For the above Timezone constants (altzone,daylight,timezone, andtzname), the value is determined by the timezone rules in effect at module load time or the last timetzset()is called and may be incorrect for times in the past. It is recommended to use thetm_gmtoffand tm_zoneresults fromlocaltime()to obtain timezone information.

See also

Moduledatetime

More object-oriented interface to dates and times.

Modulelocale

Internationalization services. The locale setting affects the interpretation of many format specifiers instrftime()andstrptime().

Modulecalendar

General calendar-related functions.timegm()is the inverse ofgmtime()from this module.

Footnotes

[1] (1,2,3)

The use of%Zis now deprecated, but the%zescape that expands to the preferred hour/minute offset is not supported by all ANSI C libraries. Also, a strict reading of the original 1982RFC 822standard calls for a two-digit year (%yrather than%Y), but practice moved to 4-digit years long before the year 2000. After that,RFC 822became obsolete and the 4-digit year has been first recommended byRFC 1123and then mandated byRFC 2822.