122 lines
4.3 KiB
TeX
122 lines
4.3 KiB
TeX
\section{Built-in Module \sectcode{time}}
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\bimodindex{time}
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This module provides various time-related functions.
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It is always available.
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An explanation of some terminology and conventions is in order.
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\begin{itemize}
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\item
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The ``epoch'' is the point where the time starts. On January 1st of that
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year, at 0 hours, the ``time since the epoch'' is zero. For UNIX, the
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epoch is 1970. To find out what the epoch is, look at \code{gmtime(0)}.
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\item
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UTC is Coordinated Universal Time (formerly known as Greenwich Mean
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Time). The acronym UTC is not a mistake but a compromise between
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English and French.
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\item
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DST is Daylight Saving Time, an adjustment of the timezone by
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(usually) one hour during part of the year. DST rules are magic
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(determined by local law) and can change from year to year. The C
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library has a table containing the local rules (often it is read from
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a system file for flexibility) and is the only source of True Wisdom
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in this respect.
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\item
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The precision of the various real-time functions may be less than
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suggested by the units in which their value or argument is expressed.
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E.g.\ on most UNIX systems, the clock ``ticks'' only 50 or 100 times a
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second, and on the Mac, times are only accurate to whole seconds.
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\end{itemize}
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The module defines the following functions and data items:
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\renewcommand{\indexsubitem}{(in module time)}
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\begin{datadesc}{altzone}
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The offset of the local DST timezone, in seconds west of the 0th
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meridian, if one is defined. Negative if the local DST timezone is
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east of the 0th meridian (as in Western Europe, including the UK).
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Only use this if \code{daylight} is nonzero.
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\end{datadesc}
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\begin{funcdesc}{asctime}{tuple}
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Convert a tuple representing a time as returned by \code{gmtime()} or
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\code{localtime()} to a 24-character string of the following form:
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\code{'Sun Jun 20 23:21:05 1993'}. Note: unlike the C function of
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the same name, there is no trailing newline.
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\end{funcdesc}
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\begin{funcdesc}{clock}{}
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Return the current CPU time as a floating point number expressed in
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seconds. The precision, and in fact the very definiton of the meaning
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of ``CPU time'', depends on that of the C function of the same name.
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\end{funcdesc}
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\begin{funcdesc}{ctime}{secs}
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Convert a time expressed in seconds since the epoch to a string
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representing local time. \code{ctime(t)} is equivalent to
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\code{asctime(localtime(t))}.
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\end{funcdesc}
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\begin{datadesc}{daylight}
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Nonzero if a DST timezone is defined.
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\end{datadesc}
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\begin{funcdesc}{gmtime}{secs}
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Convert a time expressed in seconds since the epoch to a tuple of 9
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integers, in UTC: year (e.g.\ 1993), month (1--12), day (1--31), hour
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(0--23), minute (0--59), second (0--59), weekday (0--6, monday is 0),
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Julian day (1--366), dst flag (always zero). Fractions of a second are
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ignored. Note subtle differences with the C function of this name.
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\end{funcdesc}
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\begin{funcdesc}{localtime}{secs}
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Like \code{gmtime} but converts to local time. The dst flag is set
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to 1 when DST applies to the given time.
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\end{funcdesc}
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\begin{funcdesc}{mktime}{tuple}
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This is the inverse function of \code{localtime}. Its argument is the
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full 9-tuple (since the dst flag is needed). It returns an integer.
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\end{funcdesc}
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\begin{funcdesc}{sleep}{secs}
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Suspend execution for the given number of seconds. The argument may
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be a floating point number to indicate a more precise sleep time.
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\end{funcdesc}
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\begin{funcdesc}{strftime}{format, tuple}
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Convert a tuple representing a time as returned by \code{gmtime()} or
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\code{localtime()} to a string as specified by the format argument.
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See the \code{strftime(3)} man page for details of the syntax of
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format strings.
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\end{funcdesc}
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\begin{funcdesc}{time}{}
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Return the time as a floating point number expressed in seconds since
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the epoch, in UTC. Note that even though the time is always returned
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as a floating point number, not all systems provide time with a better
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precision than 1 second.
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\end{funcdesc}
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\begin{datadesc}{timezone}
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The offset of the local (non-DST) timezone, in seconds west of the 0th
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meridian (i.e. negative in most of Western Europe, positive in the US,
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zero in the UK).
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\end{datadesc}
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\begin{datadesc}{tzname}
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A tuple of two strings: the first is the name of the local non-DST
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timezone, the second is the name of the local DST timezone. If no DST
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timezone is defined, the second string should not be used.
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\end{datadesc}
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