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(python2.1-lib.info)time
Time access and conversions
===========================
Time access and conversions.
This module provides various time-related functions. It is always
available, but not all functions are available on all 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 time tuple (see below) generally
require a 4-digit year. For backward compatibility, 2-digit years
are supported if the module variable `accept2dyear' is a non-zero
integer; this variable is initialized to `1' unless the
environment variable `PYTHONY2K' is set to a non-empty string, in
which case it is initialized to `0'. Thus, you can set
`PYTHONY2K' 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.
Note that this is new as of Python 1.5.2(a2); earlier versions, up
to Python 1.5.1 and 1.5.2a1, would add 1900 to year values below
1900.
* 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, and on the Mac, times are only accurate to
whole seconds.
* On the other hand, the precision of `time()' and `sleep()' 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), and
`sleep()' will accept a time with a nonzero fraction (UNIX
`select()' is used to implement this, where available).
* The time tuple as returned by `gmtime()', `localtime()', and
`strptime()', and accepted by `asctime()', `mktime()' and
`strftime()', is a tuple of 9 integers:
Index Field Values
------ ----- -----
0 year (e.g. 1993)
1 month range [1,12]
2 day range [1,31]
3 hour range [0,23]
4 minute range [0,59]
5 second range [0,61]; see
*(1)* in `strftime()'
description
6 weekday range [0,6], Monday
is 0
7 Julian day range [1,366]
8 daylight savings flag 0, 1 or -1; see below
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. A `-1' argument as daylight
savings flag, passed to `mktime()' will usually result in the
correct daylight savings state to be filled in.
The module defines the following functions and data items:
`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.
`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.
`asctime([tuple])'
Convert a tuple 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 TUPLE is not provided, the
current time as returned by `localtime()' is used. Note: unlike
the C function of the same name, there is no trailing newline.
_Changed in Python version 2.1_
`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 the nearest approximation to
wall-clock time since the first call to this function, based on the
Win32 function `QueryPerformanceCounter()'. The resolution is
typically better than one microsecond.
`ctime([secs])'
Convert a time expressed in seconds since the epoch to a string
representing local time. If SECS is not provided, the current time
as returned by `time()' is used. `ctime(SECS)' is equivalent to
`asctime(localtime(SECS))'. _Changed in Python version 2.1_
`daylight'
Nonzero if a DST timezone is defined.
`gmtime([secs])'
Convert a time expressed in seconds since the epoch to a time tuple
in UTC in which the dst flag is always zero. If SECS is not
provided, the current time as returned by `time()' is used.
Fractions of a second are ignored. See above for a description of
the tuple lay-out. _Changed in Python version 2.1_
`localtime([secs])'
Like `gmtime()' but converts to local time. The dst flag is set
to `1' when DST applies to the given time. _Changed in Python
version 2.1_
`mktime(tuple)'
This is the inverse function of `localtime()'. Its argument is
the 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, `OverflowError' is raised.
`sleep(secs)'
Suspend execution 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.
`strftime(format[, tuple])'
Convert a tuple representing a time as returned by `gmtime()' or
`localtime()' to a string as specified by the FORMAT argument. If
TUPLE is not provided, the current time as returned by
`localtime()' is used. FORMAT must be a string. _Changed in
Python version 2.1_
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.
%S Second as a decimal (1)
number [00,61].
%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.
%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
Sunday are considered
to be in week 0.
%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 (or by
no characters if no
time zone exists).
%% A literal `%'
character.
Notes:
`(1)'
The range really is `0' to `61'; this accounts for leap
seconds and the (very rare) double leap seconds.
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.
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.
`strptime(string[, format])'
Parse a string representing a time according to a format. The
return value is a tuple 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()'. The same
platform caveats apply; see the local UNIX documentation for
restrictions or additional supported directives. If STRING cannot
be parsed according to FORMAT, `ValueError' is raised. Values
which are not provided as part of the input string are filled in
with default values; the specific values are platform-dependent as
the XPG standard does not provide sufficient information to
constrain the result.
*Note:* This function relies entirely on the underlying platform's
C library for the date parsing, and some of these libraries are
buggy. There's nothing to be done about this short of a new,
portable implementation of `strptime()'.
Availability: Most modern UNIX systems.
`time()'
Return the time as a floating point number expressed in seconds
since the epoch, in UTC. 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.
`timezone'
The offset of the local (non-DST) timezone, in seconds west of UTC
(i.e. negative in most of Western Europe, positive in the US, zero
in the UK).
`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 also:
Note: locale Internationalization services. The locale settings
can affect the return values for some of the functions in the
`time' module.
---------- Footnotes ----------
(1) The use of `%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. The 4-digit year has been
mandated by RFC 2822 , which obsoletes RFC 822 .
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