\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. 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 time tuple (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 tuple as returned by \function{gmtime()}, \function{localtime()}, and \function{strptime()}, and accepted by \function{asctime()}, \function{mktime()} and \function{strftime()}, is a tuple of 9 integers: \begin{tableiii}{r|l|l}{textrm}{Index}{Field}{Values} \lineiii{0}{year}{(for example, 1993)} \lineiii{1}{month}{range [1,12]} \lineiii{2}{day}{range [1,31]} \lineiii{3}{hour}{range [0,23]} \lineiii{4}{minute}{range [0,59]} \lineiii{5}{second}{range [0,61]; see \strong{(1)} in \function{strftime()} description} \lineiii{6}{weekday}{range [0,6], Monday is 0} \lineiii{7}{Julian day}{range [1,366]} \lineiii{8}{daylight savings flag}{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 daylight savings flag, passed to \function{mktime()} will usually result in the correct daylight savings state to be filled in. \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{tuple}} Convert a tuple 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{tuple} is not provided, the current time as returned by \function{localtime()} is used. Note: unlike the C function of the same name, there is no trailing newline. \versionchanged[Allowed \var{tuple} to be omitted]{2.1} \end{funcdesc} \begin{funcdesc}{clock}{} 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. \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, the current time as returned by \function{time()} is used. \code{ctime(\var{secs})} is equivalent to \code{asctime(localtime(\var{secs}))}. \versionchanged[Allowed \var{secs} to be omitted]{2.1} \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 time tuple in UTC in which the dst flag is always zero. If \var{secs} is not provided, the current time as returned by \function{time()} is used. Fractions of a second are ignored. See above for a description of the tuple lay-out. \versionchanged[Allowed \var{secs} to be omitted]{2.1} \end{funcdesc} \begin{funcdesc}{localtime}{\optional{secs}} Like \function{gmtime()} but converts to local time. The dst flag is set to \code{1} when DST applies to the given time. \versionchanged[Allowed \var{secs} to be omitted]{2.1} \end{funcdesc} \begin{funcdesc}{mktime}{tuple} This is the inverse function of \function{localtime()}. Its argument is the 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, \exception{OverflowError} is raised. \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{, tuple}} Convert a tuple representing a time as returned by \function{gmtime()} or \function{localtime()} to a string as specified by the \var{format} argument. If \var{tuple} is not provided, the current time as returned by \function{localtime()} is used. \var{format} must be a string. \versionchanged[Allowed \var{tuple} to be omitted]{2.1} 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.}{} \lineiii{\%S}{Second as a decimal number [00,61].}{(1)} \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.}{} \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 Sunday are considered to be in week 0.}{} \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 (or by no characters if no time zone exists).}{} \lineiii{\%\%}{A literal \character{\%} character.}{} \end{tableiii} \noindent Notes: \begin{description} \item[(1)] The range really is \code{0} to \code{61}; this accounts for leap seconds and the (very rare) double leap seconds. \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 tuple 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()}. The same platform caveats apply; see the local \UNIX{} documentation for restrictions or additional supported directives. If \var{string} cannot be parsed according to \var{format}, \exception{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. \strong{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 \cfunction{strptime()}. Availability: Most modern \UNIX{} systems. \end{funcdesc} \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. \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{seealso} \seemodule{locale}{Internationalization services. The locale settings can affect the return values for some of the functions in the \module{time} module.} \end{seealso}