mirror of https://github.com/python/cpython.git
219 lines
8.9 KiB
TeX
219 lines
8.9 KiB
TeX
\section{Built-in Module \module{time}}
|
|
\declaremodule{builtin}{time}
|
|
|
|
\modulesynopsis{Time access and conversions.}
|
|
|
|
|
|
This module provides various time-related functions.
|
|
It is always available.
|
|
|
|
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)}.%
|
|
\index{epoch}
|
|
|
|
\item
|
|
The functions in this module don't 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
|
|
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.%
|
|
\index{Year 2000}%
|
|
\index{Y2K}
|
|
|
|
\item
|
|
UTC is Coordinated Universal Time (formerly known as Greenwich Mean
|
|
Time). The acronym UTC is not a mistake but a compromise between
|
|
English and French.%
|
|
\index{UTC}%
|
|
\index{Coordinated Universal Time}%
|
|
\index{Greenwich Mean Time}
|
|
|
|
\item
|
|
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.%
|
|
\index{Daylight Saving Time}
|
|
|
|
\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: year (e.g.\ 1993), month (1--12), day (1--31),
|
|
hour (0--23), minute (0--59), second (0--59), weekday (0--6, monday is
|
|
0), Julian day (1--366) and daylight savings flag (-1, 0 or 1).
|
|
Note that unlike the \C{} structure, the month value is a range of 1-12, not
|
|
0-11. A year value less than 100 will typically be silently converted to
|
|
1900 plus the year value. 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}{altzone}
|
|
The offset of the local DST timezone, in seconds west of the 0th
|
|
meridian, if one is defined. Negative if the local DST timezone is
|
|
east of the 0th meridian (as in Western Europe, including the UK).
|
|
Only use this if \code{daylight} is nonzero.
|
|
\end{datadesc}
|
|
|
|
\begin{funcdesc}{asctime}{tuple}
|
|
Convert a tuple representing a time as returned by \code{gmtime()} or
|
|
\code{localtime()} to a 24-character string of the following form:
|
|
\code{'Sun Jun 20 23:21:05 1993'}. Note: unlike the C function of
|
|
the same name, there is no trailing newline.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{clock}{}
|
|
Return the current CPU time as a floating point number expressed in
|
|
seconds. The precision, and in fact the very definiton of the meaning
|
|
of ``CPU time''\index{CPU 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}{secs}
|
|
Convert a time expressed in seconds since the epoch to a string
|
|
representing local time. \code{ctime(\var{secs})} is equivalent to
|
|
\code{asctime(localtime(\var{secs}))}.
|
|
\end{funcdesc}
|
|
|
|
\begin{datadesc}{daylight}
|
|
Nonzero if a DST timezone is defined.
|
|
\end{datadesc}
|
|
|
|
\begin{funcdesc}{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. Fractions of a second are
|
|
ignored. See above for a description of the tuple lay-out.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{localtime}{secs}
|
|
Like \function{gmtime()} but converts to local time. The dst flag is
|
|
set to \code{1} when DST applies to the given time.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{mktime}{tuple}
|
|
This is the inverse function of \code{localtime}. Its argument is the
|
|
full 9-tuple (since the dst flag is needed --- pass \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.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{strftime}{format, tuple}
|
|
Convert a tuple representing a time as returned by \code{gmtime()} or
|
|
\code{localtime()} to a string as specified by the format argument.
|
|
|
|
The following directives, shown without the optional field width and
|
|
precision specification, are replaced by the indicated characters:
|
|
|
|
\begin{tableii}{c|p{24em}}{code}{Directive}{Meaning}
|
|
\lineii{\%a}{Locale's abbreviated weekday name.}
|
|
\lineii{\%A}{Locale's full weekday name.}
|
|
\lineii{\%b}{Locale's abbreviated month name.}
|
|
\lineii{\%B}{Locale's full month name.}
|
|
\lineii{\%c}{Locale's appropriate date and time representation.}
|
|
\lineii{\%d}{Day of the month as a decimal number [01,31].}
|
|
\lineii{\%H}{Hour (24-hour clock) as a decimal number [00,23].}
|
|
\lineii{\%I}{Hour (12-hour clock) as a decimal number [01,12].}
|
|
\lineii{\%j}{Day of the year as a decimal number [001,366].}
|
|
\lineii{\%m}{Month as a decimal number [01,12].}
|
|
\lineii{\%M}{Minute as a decimal number [00,59].}
|
|
\lineii{\%p}{Locale's equivalent of either AM or PM.}
|
|
\lineii{\%S}{Second as a decimal number [00,61].}
|
|
\lineii{\%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.}
|
|
\lineii{\%w}{Weekday as a decimal number [0(Sunday),6].}
|
|
\lineii{\%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.}
|
|
\lineii{\%x}{Locale's appropriate date representation.}
|
|
\lineii{\%X}{Locale's appropriate time representation.}
|
|
\lineii{\%y}{Year without century as a decimal number [00,99].}
|
|
\lineii{\%Y}{Year with century as a decimal number.}
|
|
\lineii{\%Z}{Time zone name (or by no characters if no time zone exists).}
|
|
\lineii{\%\%}{\%}
|
|
\end{tableii}
|
|
|
|
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 \code{\%} 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 \code{gmtime()} or \code{localtime()}.
|
|
The format uses the same directives as those used by
|
|
\code{strftime()}; it defaults to \code{"\%a \%b \%d \%H:\%M:\%S \%Y"}
|
|
which matches the formatting returned by \code{ctime()}. The same
|
|
platform caveats apply; see the local Unix documentation for
|
|
restrictions or additional supported directives. This function may
|
|
not be defined on all platforms.
|
|
|
|
\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 the 0th
|
|
meridian (i.e. 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}
|
|
|