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| -rw-r--r-- | Doc/lib/libtime.tex | 56 |
1 files changed, 25 insertions, 31 deletions
diff --git a/Doc/lib/libtime.tex b/Doc/lib/libtime.tex index 82007f7..1c9ffe9 100644 --- a/Doc/lib/libtime.tex +++ b/Doc/lib/libtime.tex @@ -16,23 +16,22 @@ An explanation of some terminology and conventions is in order. 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} +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} +determined by the C library; for \UNIX{}, it is typically in +2038\index{Year 2038}. \item -\strong{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. 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 +\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 @@ -41,26 +40,21 @@ 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.% -\index{Year 2000}% -\index{Y2K} +would add 1900 to year values below 1900. \item -UTC is Coordinated Universal Time (formerly known as Greenwich Mean -Time, or GMT). The acronym UTC is not a mistake but a compromise -between English and French.% -\index{UTC}% -\index{Coordinated Universal Time}% -\index{Greenwich Mean Time} +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, 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} +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 @@ -84,7 +78,7 @@ The time tuple as returned by \function{gmtime()}, 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 +1). 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 descibed under ``Year 2000 (Y2K) issues'' above. A \code{-1} argument as daylight savings flag, passed to \function{mktime()} will usually result in the @@ -112,14 +106,14 @@ Only use this if \code{daylight} is nonzero. \begin{funcdesc}{asctime}{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'}. Note: unlike the \C{} function of +\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 ``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} @@ -199,7 +193,7 @@ specification, and are replaced by the indicated characters in the \end{tableii} Additional directives may be supported on certain platforms, but -only the ones listed here have a meaning standardized by ANSI \C{}. +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 |