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202 lines
8.7 KiB
TeX
202 lines
8.7 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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\item
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The time tuple as returned by \code{gmtime()} and \code{localtime()},
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or as accpted by \code{mktime()} is a tuple of 9
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integers: 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) and daylight savings flag (-1, 0 or 1).
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Note that unlike the C structure, the month value is a range of 1-12, not
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0-11. A year value of $<$ 100 will typically be silently converted to
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1900 $+$ year value. A -1 argument as daylight savings flag, passed to
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\code{mktime()} will usually result in the correct daylight savings
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state to be filled in.
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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 time tuple
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in UTC in which the dst flag is always zero. Fractions of a second are
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ignored.
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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 --- pass -1 as the dst flag if
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it is unknown) which expresses the time
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in \em{local} time, not UTC. It returns a floating
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point number, for compatibility with \code{time.time()}. If the input
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value can't be represented as a valid time, OverflowError is raised.
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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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The following directives, shown without the optional field width and
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precision specification, are replaced by the indicated characters:
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\begin{tabular}{lp{25em}}
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\%a & Locale's abbreviated weekday name. \\
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\%A & Locale's full weekday name. \\
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\%b & Locale's abbreviated month name. \\
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\%B & Locale's full month name. \\
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\%c & Locale's appropriate date and time representation. \\
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\%d & Day of the month as a decimal number [01,31]. \\
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\%E & Locale's combined Emperor/Era name and year. \\
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\%H & Hour (24-hour clock) as a decimal number [00,23]. \\
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\%I & Hour (12-hour clock) as a decimal number [01,12]. \\
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\%j & Day of the year as a decimal number [001,366]. \\
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\%m & Month as a decimal number [01,12]. \\
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\%M & Minute as a decimal number [00,59]. \\
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\%n & New-line character. \\
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\%N & Locale's Emperor/Era name. \\
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\%o & Locale's Emperor/Era year. \\
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\%p & Locale's equivalent of either AM or PM. \\
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\%S & Second as a decimal number [00,61]. \\
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\%t & Tab character. \\
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\%U & Week number of the year (Sunday as the first day of the
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week) as a decimal number [00,53]. All days in a new
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year preceding the first Sunday are considered to be in
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week 0. \\
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\%w & Weekday as a decimal number [0(Sunday),6]. \\
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\%W & Week number of the year (Monday as the first day of the
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week) as a decimal number [00,53]. All days in a new
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year preceding the first Sunday are considered to be in
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week 0. \\
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\%x & Locale's appropriate date representation. \\
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\%X & Locale's appropriate time representation. \\
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\%y & Year without century as a decimal number [00,99]. \\
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\%Y & Year with century as a decimal number. \\
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\%Z & Time zone name (or by no characters if no time zone
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exists). \\
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\%\% & \% \\
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\end{tabular}
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An optional field width and precision specification can immediately
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follow the initial \% of a directive in the following order: \\
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\begin{tabular}{lp{25em}}
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[-|0]w & the decimal digit string w specifies a minimum field
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width in which the result of the conversion is right-
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or left-justified. It is right-justified (with space
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padding) by default. If the optional flag `-' is
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specified, it is left-justified with space padding on
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the right. If the optional flag `0' is specified, it
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is right-justified and padded with zeros on the left. \\
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.p & the decimal digit string p specifies the minimum number
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of digits to appear for the d, H, I, j, m, M, o, S, U,
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w, W, y and Y directives, and the maximum number of
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characters to be used from the a, A, b, B, c, D, E, F,
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h, n, N, p, r, t, T, x, X, z, Z, and % directives. In
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the first case, if a directive supplies fewer digits
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than specified by the precision, it will be expanded
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with leading zeros. In the second case, if a directive
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supplies more characters than specified by the
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precision, excess characters will truncated on the
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right.
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\end{tabular}
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If no field width or precision is specified for a d, H, I, m, M, S, U,
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W, y, or j directive, a default of .2 is used for all but j for which
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.3 is used.
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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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