time
--- Time access and conversionsThis module provides various time-related functions. For related
functionality, see also the datetime
and calendar
modules.
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.
- The epoch is the point where the time starts. On January 1st of that
year, at 0 hours, the "time since the epoch" is zero. For Unix, the epoch is
1970. To find out what the epoch is, look at
gmtime(0)
.
- The functions in this module do not handle dates and times before the epoch or far in the future. The cut-off point in the future is determined by the C library; for Unix, it is typically in 2038.
- Year 2000 (Y2K) issues: Python depends on the platform's C library, which
generally doesn't have year 2000 issues, since all dates and times are
represented internally as seconds since the epoch. Functions accepting a
struct_time
(see below) generally require a 4-digit year. For backward compatibility, 2-digit years are supported if the module variableaccept2dyear
is a non-zero integer; this variable is initialized to1
unless the environment variablePYTHONY2K
is set to a non-empty string, in which case it is initialized to0
. Thus, you can setPYTHONY2K
to a non-empty string in the environment to require 4-digit years for all year input. When 2-digit years are accepted, they are converted according to the POSIX or X/Open standard: values 69-99 are mapped to 1969-1999, and values 0--68 are mapped to 2000--2068. Values 100--1899 are always illegal.
- 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 of
time()
andsleep()
is better than their Unix equivalents: times are expressed as floating point numbers,time()
returns the most accurate time available (using Unixgettimeofday()
where available), andsleep()
will accept a time with a nonzero fraction (Unixselect()
is used to implement this, where available). The time value as returned by
gmtime()
,localtime()
, andstrptime()
, and accepted byasctime()
,mktime()
andstrftime()
, may be considered as a sequence of 9 integers. The return values ofgmtime()
,localtime()
, andstrptime()
also offer attribute names for individual fields.See
struct_time
for a description of these objects.Changed in version 2.2: The time value sequence was changed from a tuple to a
struct_time
, with the addition of attribute names for the fields.Use the following functions to convert between time representations:
From To Use seconds since the epoch struct_time
in UTCgmtime()
seconds since the epoch struct_time
in local timelocaltime()
struct_time
in UTCseconds since the epoch calendar.timegm()
struct_time
in local timeseconds since the epoch mktime()
The module defines the following functions and data items:
time.accept2dyear
Boolean value indicating whether two-digit year values will be accepted. This
is true by default, but will be set to false if the environment variable
PYTHONY2K
has been set to a non-empty string. It may also be modified
at run time.
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 if daylight
is nonzero.
time.asctime([t])
Convert a tuple or struct_time
representing a time as returned by
gmtime()
or localtime()
to a 24-character string of the following
form: 'Sun Jun 20 23:21:05 1993'
. If t is not provided, the current time
as returned by localtime()
is used. Locale information is not used by
asctime()
.
Note
Unlike the C function of the same name, there is no trailing newline.
Changed in version 2.1: Allowed t to be omitted.
time.clock()
On Unix, return the current processor time as a floating point number expressed in seconds. The precision, and in fact the very definition of the meaning of "processor time", depends on that of the C function of the same name, but in any case, this is the function to use for benchmarking Python or timing algorithms.
On Windows, this function returns wall-clock seconds elapsed since the first
call to this function, as a floating point number, based on the Win32 function
QueryPerformanceCounter()
. The resolution is typically better than one
microsecond.
time.ctime([secs])
Convert a time expressed in seconds since the epoch to a string representing
local time. If secs is not provided or None
, the current time as
returned by time()
is used. ctime(secs)
is equivalent to
asctime(localtime(secs))
. Locale information is not used by ctime()
.
Changed in version 2.1: Allowed secs to be omitted.
Changed in version 2.4: If secs is None
, the current time is used.
time.daylight
Nonzero if a DST timezone is defined.
time.gmtime([secs])
Convert a time expressed in seconds since the epoch to a struct_time
in
UTC in which the dst flag is always zero. If secs is not provided or
None
, the current time as returned by time()
is used. Fractions
of a second are ignored. See above for a description of the
struct_time
object. See calendar.timegm()
for the inverse of this
function.
Changed in version 2.1: Allowed secs to be omitted.
Changed in version 2.4: If secs is None
, the current time is used.
time.localtime([secs])
Like gmtime()
but converts to local time. If secs is not provided or
None
, the current time as returned by time()
is used. The dst
flag is set to 1
when DST applies to the given time.
Changed in version 2.1: Allowed secs to be omitted.
Changed in version 2.4: If secs is None
, the current time is used.
time.mktime(t)
This is the inverse function of localtime()
. Its argument is the
struct_time
or full 9-tuple (since the dst flag is needed; use -1
as the dst flag if it is unknown) which expresses the time in local time, not
UTC. It returns a floating point number, for compatibility with time()
.
If the input value cannot be represented as a valid time, either
OverflowError
or ValueError
will 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.sleep(secs)
Suspend execution of the current thread for the given number of seconds.
The argument may be a floating point number to indicate a more precise sleep
time. The actual suspension time may be less than that requested because any
caught signal will terminate the sleep()
following execution of that
signal's catching routine. Also, the suspension time may be longer than
requested by an arbitrary amount because of the scheduling of other activity
in the system.
time.strftime(format[, t])
Convert a tuple or struct_time
representing a time as returned by
gmtime()
or localtime()
to a string as specified by the format
argument. If t is not provided, the current time as returned by
localtime()
is used. format must be a string. ValueError
is
raised if any field in t is outside of the allowed range. strftime()
returns a locale depedent byte string; the result may be converted to unicode
by doing strftime(<myformat>).decode(locale.getlocale()[1])
.
Changed in version 2.1: Allowed t to be omitted.
Changed in version 2.4: ValueError
raised if a field in t is out of range.
Changed in version 2.5: 0 is now 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 the format string. They are shown
without the optional field width and precision specification, and are replaced
by the indicated characters in the strftime()
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]. | |
%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. | (1) |
%S | Second as a decimal number [00,61]. | (2) |
%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. | (3) |
%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. | (3) |
%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 name (no characters if no time zone exists). | |
%% | A literal '%' character. |
Notes:
- When used with the
strptime()
function, the%p
directive only affects the output hour field if the%I
directive is used to parse the hour. - The range really is
0
to61
; this accounts for leap seconds and the (very rare) double leap seconds. - When used with the
strptime()
function,%U
and%W
are 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 2822 Internet email standard. 1
>>> from time import gmtime, 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 the [UNKNOWN NODE manpage] 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 %j
where
it is 3.
time.strptime(string[, format])
Parse a string representing a time according to a format. The return value is
a struct_time
as returned by gmtime()
or localtime()
.
The format parameter uses the same directives as those used by
strftime()
; it defaults to "%a %b %d %H:%M:%S %Y"
which matches the
formatting returned by ctime()
. If string cannot be parsed according to
format, or if it has excess data after parsing, ValueError
is 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)
.
For example:
[UNKNOWN NODE doctest_block]Support for the %Z
directive is based on the values contained in tzname
and whether daylight
is 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. But strptime()
is independent of any platform
and thus does not necessarily support all directives available that are not
documented as supported.
class time.struct_time
The type of the time value sequence returned by gmtime()
,
localtime()
, and strptime()
. It is an object with a named
tuple interface: 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]; see (2) in
strftime() description |
6 | tm_wday | range [0, 6], Monday is 0 |
7 | tm_yday | range [1, 366] |
8 | tm_isdst | 0, 1 or -1; see below |
New in version 2.2.
Note that unlike the C structure, the month value is a range of [1, 12], not [0, 11]. A year value will be handled as described under Year 2000 (Y2K) issues above.
In calls to mktime()
, tm_isdst
may 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
TypeError
is raised.
time.time()
Return the time in seconds since the epoch as a floating point number. 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.
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).
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.
time.tzset()
Reset the time conversion rules used by the library routines. The environment
variable TZ
specifies how this is done. It will also set the variables
tzname
(from the TZ
environment variable), timezone
(non-DST
seconds West of UTC), altzone
(DST seconds west of UTC) and daylight
(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).
New in version 2.3.
Availability: Unix.
Note
Although in many cases, changing the TZ
environment variable may
affect the output of functions like localtime()
without calling
tzset()
, this behavior should not be relied on.
The TZ
environment variable should contain no whitespace.
The standard format of the TZ
environment variable is (whitespace
added for clarity):
std offset [dst [offset [,start[/time], end[/time]]]]
Where the components are:
std
anddst
- 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 day n (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
- The d'th day (0 <= d <= 6) or week n of month m of the year (1 <= n <= 5, 1 <= m <= 12, where week 5 means "the last d day in month m" which may occur in either the fourth or the fifth week). Week 1 is the first week in which the d'th day occurs. Day zero is Sunday.
time
has the same format asoffset
except 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 ([UNKNOWN NODE manpage]) database to
specify the timezone rules. To do this, set the TZ
environment
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')
See also
- Module
datetime
- More object-oriented interface to dates and times.
- Module
locale
- Internationalization services. The locale setting affects the interpretation
of many format specifiers in
strftime()
andstrptime()
. - Module
calendar
- General calendar-related functions.
timegm()
is the inverse ofgmtime()
from this module.
Footnotes
%Z
is now deprecated, but the %z
escape that expands to the
preferred hour/minute offset is not supported by all ANSI C libraries. Also, a
strict reading of the original 1982 RFC 822 standard calls for a two-digit
year (%y rather than %Y), but practice moved to 4-digit years long before the
year 2000. After that, RFC 822 became obsolete and the 4-digit year has
been first recommended by RFC 1123 and then mandated by RFC 2822.