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-\section{\module{time} ---
- Time access and conversions}
-
-\declaremodule{builtin}{time}
-\modulesynopsis{Time access and conversions.}
-
-
-This module provides various time-related functions. It is always
-available, but 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.
-
-\begin{itemize}
-
-\item
-The \dfn{epoch}\index{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 \code{gmtime(0)}.
-
-\item
-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\index{Year 2038}.
-
-\item
-\strong{Year 2000 (Y2K) issues}:\index{Year 2000}\index{Y2K} 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 \class{struct_time}
-(see below) generally require a 4-digit year. For backward
-compatibility, 2-digit years are supported if the module variable
-\code{accept2dyear} is a non-zero integer; this variable is
-initialized to \code{1} unless the environment variable
-\envvar{PYTHONY2K} is set to a non-empty string, in which case it is
-initialized to \code{0}. Thus, you can set
-\envvar{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.
-
-\item
-UTC\index{UTC} is Coordinated Universal Time\index{Coordinated
-Universal Time} (formerly known as Greenwich Mean
-Time,\index{Greenwich Mean Time} or GMT). The acronym UTC is not a
-mistake but a compromise between English and French.
-
-\item
-DST is Daylight Saving Time,\index{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.
-
-\item
-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.
-
-\item
-On the other hand, the precision of \function{time()} and
-\function{sleep()} is better than their \UNIX{} equivalents: times are
-expressed as floating point numbers, \function{time()} returns the
-most accurate time available (using \UNIX{} \cfunction{gettimeofday()}
-where available), and \function{sleep()} will accept a time with a
-nonzero fraction (\UNIX{} \cfunction{select()} is used to implement
-this, where available).
-
-\item
-The time value as returned by \function{gmtime()},
-\function{localtime()}, and \function{strptime()}, and accepted by
-\function{asctime()}, \function{mktime()} and \function{strftime()},
-is a sequence of 9 integers. The return values of \function{gmtime()},
-\function{localtime()}, and \function{strptime()} also offer attribute
-names for individual fields.
-
-\begin{tableiii}{c|l|l}{textrm}{Index}{Attribute}{Values}
- \lineiii{0}{\member{tm_year}}{(for example, 1993)}
- \lineiii{1}{\member{tm_mon}}{range [1,12]}
- \lineiii{2}{\member{tm_mday}}{range [1,31]}
- \lineiii{3}{\member{tm_hour}}{range [0,23]}
- \lineiii{4}{\member{tm_min}}{range [0,59]}
- \lineiii{5}{\member{tm_sec}}{range [0,61]; see \strong{(1)} in \function{strftime()} description}
- \lineiii{6}{\member{tm_wday}}{range [0,6], Monday is 0}
- \lineiii{7}{\member{tm_yday}}{range [1,366]}
- \lineiii{8}{\member{tm_isdst}}{0, 1 or -1; see below}
-\end{tableiii}
-
-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 \code{-1} argument as the
-daylight savings flag, passed to \function{mktime()} will usually
-result in the correct daylight savings state to be filled in.
-
-When a tuple with an incorrect length is passed to a function
-expecting a \class{struct_time}, or having elements of the wrong type, a
-\exception{TypeError} is raised.
-
-\versionchanged[The time value sequence was changed from a tuple to a
- \class{struct_time}, with the addition of attribute names
- for the fields]{2.2}
-\end{itemize}
-
-The module defines the following functions and data items:
-
-
-\begin{datadesc}{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 \envvar{PYTHONY2K} has been set to a non-empty
-string. It may also be modified at run time.
-\end{datadesc}
-
-\begin{datadesc}{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
-\code{daylight} is nonzero.
-\end{datadesc}
-
-\begin{funcdesc}{asctime}{\optional{t}}
-Convert a tuple or \class{struct_time} representing a time as returned
-by \function{gmtime()}
-or \function{localtime()} to a 24-character string of the following form:
-\code{'Sun Jun 20 23:21:05 1993'}. If \var{t} is not provided, the
-current time as returned by \function{localtime()} is used.
-Locale information is not used by \function{asctime()}.
-\note{Unlike the C function of the same name, there is no trailing
-newline.}
-\versionchanged[Allowed \var{t} to be omitted]{2.1}
-\end{funcdesc}
-
-\begin{funcdesc}{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''\index{CPU time}\index{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\index{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 \cfunction{QueryPerformanceCounter()}.
-The resolution is typically better than one microsecond.
-\end{funcdesc}
-
-\begin{funcdesc}{ctime}{\optional{secs}}
-Convert a time expressed in seconds since the epoch to a string
-representing local time. If \var{secs} is not provided or
-\constant{None}, the current time as returned by \function{time()} is
-used. \code{ctime(\var{secs})} is equivalent to
-\code{asctime(localtime(\var{secs}))}.
-Locale information is not used by \function{ctime()}.
-\versionchanged[Allowed \var{secs} to be omitted]{2.1}
-\versionchanged[If \var{secs} is \constant{None}, the current time is
- used]{2.4}
-\end{funcdesc}
-
-\begin{datadesc}{daylight}
-Nonzero if a DST timezone is defined.
-\end{datadesc}
-
-\begin{funcdesc}{gmtime}{\optional{secs}}
-Convert a time expressed in seconds since the epoch to a \class{struct_time}
-in UTC in which the dst flag is always zero. If \var{secs} is not
-provided or \constant{None}, the current time as returned by
-\function{time()} is used. Fractions of a second are ignored. See
-above for a description of the \class{struct_time} object. See
-\function{calendar.timegm()} for the inverse of this function.
-\versionchanged[Allowed \var{secs} to be omitted]{2.1}
-\versionchanged[If \var{secs} is \constant{None}, the current time is
- used]{2.4}
-\end{funcdesc}
-
-\begin{funcdesc}{localtime}{\optional{secs}}
-Like \function{gmtime()} but converts to local time. If \var{secs} is
-not provided or \constant{None}, the current time as returned by
-\function{time()} is used. The dst flag is set to \code{1} when DST
-applies to the given time.
-\versionchanged[Allowed \var{secs} to be omitted]{2.1}
-\versionchanged[If \var{secs} is \constant{None}, the current time is
- used]{2.4}
-\end{funcdesc}
-
-\begin{funcdesc}{mktime}{t}
-This is the inverse function of \function{localtime()}. Its argument
-is the \class{struct_time} or full 9-tuple (since the dst flag is
-needed; use \code{-1} as the dst flag if it is unknown) which
-expresses the time in
-\emph{local} time, not UTC. It returns a floating point number, for
-compatibility with \function{time()}. If the input value cannot be
-represented as a valid time, either \exception{OverflowError} or
-\exception{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.
-\end{funcdesc}
-
-\begin{funcdesc}{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 \function{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.
-\end{funcdesc}
-
-\begin{funcdesc}{strftime}{format\optional{, t}}
-Convert a tuple or \class{struct_time} representing a time as returned
-by \function{gmtime()} or \function{localtime()} to a string as
-specified by the \var{format} argument. If \var{t} is not
-provided, the current time as returned by \function{localtime()} is
-used. \var{format} must be a string. \exception{ValueError} is raised
-if any field in \var{t} is outside of the allowed range.
-\versionchanged[Allowed \var{t} to be omitted]{2.1}
-\versionchanged[\exception{ValueError} raised if a field in \var{t} is
-out of range]{2.4}
-\versionchanged[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.]{2.5}
-
-
-The following directives can be embedded in the \var{format} string.
-They are shown without the optional field width and precision
-specification, and are replaced by the indicated characters in the
-\function{strftime()} result:
-
-\begin{tableiii}{c|p{24em}|c}{code}{Directive}{Meaning}{Notes}
- \lineiii{\%a}{Locale's abbreviated weekday name.}{}
- \lineiii{\%A}{Locale's full weekday name.}{}
- \lineiii{\%b}{Locale's abbreviated month name.}{}
- \lineiii{\%B}{Locale's full month name.}{}
- \lineiii{\%c}{Locale's appropriate date and time representation.}{}
- \lineiii{\%d}{Day of the month as a decimal number [01,31].}{}
- \lineiii{\%H}{Hour (24-hour clock) as a decimal number [00,23].}{}
- \lineiii{\%I}{Hour (12-hour clock) as a decimal number [01,12].}{}
- \lineiii{\%j}{Day of the year as a decimal number [001,366].}{}
- \lineiii{\%m}{Month as a decimal number [01,12].}{}
- \lineiii{\%M}{Minute as a decimal number [00,59].}{}
- \lineiii{\%p}{Locale's equivalent of either AM or PM.}{(1)}
- \lineiii{\%S}{Second as a decimal number [00,61].}{(2)}
- \lineiii{\%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)}
- \lineiii{\%w}{Weekday as a decimal number [0(Sunday),6].}{}
- \lineiii{\%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)}
- \lineiii{\%x}{Locale's appropriate date representation.}{}
- \lineiii{\%X}{Locale's appropriate time representation.}{}
- \lineiii{\%y}{Year without century as a decimal number [00,99].}{}
- \lineiii{\%Y}{Year with century as a decimal number.}{}
- \lineiii{\%Z}{Time zone name (no characters if no time zone exists).}{}
- \lineiii{\%\%}{A literal \character{\%} character.}{}
-\end{tableiii}
-
-\noindent
-Notes:
-
-\begin{description}
- \item[(1)]
- When used with the \function{strptime()} function, the \code{\%p}
- directive only affects the output hour field if the \code{\%I} directive
- is used to parse the hour.
- \item[(2)]
- The range really is \code{0} to \code{61}; this accounts for leap
- seconds and the (very rare) double leap seconds.
- \item[(3)]
- When used with the \function{strptime()} function, \code{\%U} and \code{\%W}
- are only used in calculations when the day of the week and the year are
- specified.
-\end{description}
-
-Here is an example, a format for dates compatible with that specified
-in the \rfc{2822} Internet email standard.
- \footnote{The use of \code{\%Z} is now
- deprecated, but the \code{\%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}.}
-
-\begin{verbatim}
->>> from time import gmtime, strftime
->>> strftime("%a, %d %b %Y %H:%M:%S +0000", gmtime())
-'Thu, 28 Jun 2001 14:17:15 +0000'
-\end{verbatim}
-
-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 \character{\%} of a
-directive in the following order; this is also not portable.
-The field width is normally 2 except for \code{\%j} where it is 3.
-\end{funcdesc}
-
-\begin{funcdesc}{strptime}{string\optional{, format}}
-Parse a string representing a time according to a format. The return
-value is a \class{struct_time} as returned by \function{gmtime()} or
-\function{localtime()}.
-
-The \var{format} parameter uses the same directives as those used by
-\function{strftime()}; it defaults to \code{"\%a \%b \%d \%H:\%M:\%S
- \%Y"} which matches the formatting returned by \function{ctime()}.
-If \var{string} cannot be parsed according to \var{format}, or if it
-has excess data after parsing, \exception{ValueError} is raised. The
-default values used to fill in any missing data when more accurate
-values cannot be inferred are \code{(1900, 1, 1, 0, 0, 0, 0, 1, -1)}.
-
-For example:
-
-\begin{verbatim}
->>> import time
->>> time.strptime("30 Nov 00", "%d %b %y")
-(2000, 11, 30, 0, 0, 0, 3, 335, -1)
-\end{verbatim}
-
-Support for the \code{\%Z} directive is based on the values contained in
-\code{tzname} and whether \code{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
-\code{strftime()} is implemented per platform it can sometimes offer more
-directives than those listed. But \code{strptime()} is independent of any
-platform and thus does not necessarily support all directives available that
-are not documented as supported.
-\end{funcdesc}
-
-\begin{datadesc}{struct_time}
-The type of the time value sequence returned by \function{gmtime()},
-\function{localtime()}, and \function{strptime()}.
-\versionadded{2.2}
-\end{datadesc}
-
-\begin{funcdesc}{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. 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.
-\end{funcdesc}
-
-\begin{datadesc}{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).
-\end{datadesc}
-
-\begin{datadesc}{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.
-\end{datadesc}
-
-\begin{funcdesc}{tzset}{}
-Resets the time conversion rules used by the library routines.
-The environment variable \envvar{TZ} specifies how this is done.
-\versionadded{2.3}
-
-Availability: \UNIX.
-
-\begin{notice}
-Although in many cases, changing the \envvar{TZ} environment variable
-may affect the output of functions like \function{localtime} without calling
-\function{tzset}, this behavior should not be relied on.
-
-The \envvar{TZ} environment variable should contain no whitespace.
-\end{notice}
-
-The standard format of the \envvar{TZ} environment variable is:
-(whitespace added for clarity)
-\begin{itemize}
- \item[std offset [dst [offset] [,start[/time], end[/time]]]]
-\end{itemize}
-
-Where:
-
-\begin{itemize}
- \item[std and dst]
- Three or more alphanumerics giving the timezone abbreviations.
- These will be propagated into time.tzname
-
- \item[offset]
- The offset has the form: \plusminus{} 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.
-
- \item[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:
-
- \begin{itemize}
- \item[J\var{n}]
- The Julian day \var{n} (1 <= \var{n} <= 365). Leap days are not
- counted, so in all years February 28 is day 59 and
- March 1 is day 60.
-
- \item[\var{n}]
- The zero-based Julian day (0 <= \var{n} <= 365). Leap days are
- counted, and it is possible to refer to February 29.
-
- \item[M\var{m}.\var{n}.\var{d}]
- The \var{d}'th day (0 <= \var{d} <= 6) or week \var{n}
- of month \var{m} of the year (1 <= \var{n} <= 5,
- 1 <= \var{m} <= 12, where week 5 means "the last \var{d} day
- in month \var{m}" which may occur in either the fourth or
- the fifth week). Week 1 is the first week in which the
- \var{d}'th day occurs. Day zero is Sunday.
- \end{itemize}
-
- time has the same format as offset except that no leading sign ('-' or
- '+') is allowed. The default, if time is not given, is 02:00:00.
-\end{itemize}
-
-
-\begin{verbatim}
->>> 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'
-\end{verbatim}
-
-On many \UNIX{} systems (including *BSD, Linux, Solaris, and Darwin), it
-is more convenient to use the system's zoneinfo (\manpage{tzfile}{5})
-database to specify the timezone rules. To do this, set the
-\envvar{TZ} environment variable to the path of the required timezone
-datafile, relative to the root of the systems 'zoneinfo' timezone database,
-usually located at \file{/usr/share/zoneinfo}. For example,
-\code{'US/Eastern'}, \code{'Australia/Melbourne'}, \code{'Egypt'} or
-\code{'Europe/Amsterdam'}.
-
-\begin{verbatim}
->>> os.environ['TZ'] = 'US/Eastern'
->>> time.tzset()
->>> time.tzname
-('EST', 'EDT')
->>> os.environ['TZ'] = 'Egypt'
->>> time.tzset()
->>> time.tzname
-('EET', 'EEST')
-\end{verbatim}
-
-\end{funcdesc}
-
-
-\begin{seealso}
- \seemodule{datetime}{More object-oriented interface to dates and times.}
- \seemodule{locale}{Internationalization services. The locale
- settings can affect the return values for some of
- the functions in the \module{time} module.}
- \seemodule{calendar}{General calendar-related functions.
- \function{timegm()} is the inverse of
- \function{gmtime()} from this module.}
-\end{seealso}