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Added remark about time() and sleep()'s subsecond precision. 

Added hint about using clock() for benchmarks etc.
Removed non-portable strftime directives and field width, and added a
warning about non-standard features.
This commit is contained in:
Guido van Rossum 1996-12-12 17:59:37 +00:00
parent 3486f27428
commit 21be147094
2 changed files with 34 additions and 64 deletions
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49
Doc/lib/libtime.tex
View File

@ -32,6 +32,14 @@ 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 \code{time()} and \code{sleep()}
is better than their UNIX equivalents: times are expressed as floating
point numbers, \code{time()} returns the most accurate time available
(using UNIX \code{gettimeofday()} where available), and \code{sleep()}
will accept a time with a nonzero fraction (UNIX \code{select()} is
used to implement this, where available).
\item
The time tuple as returned by \code{gmtime()} and \code{localtime()},
or as accpted by \code{mktime()} is a tuple of 9
@ -68,7 +76,9 @@ the same name, there is no trailing newline.
\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'', depends on that of the C function of the same name.
of ``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 Python
or timing algorithms.
\end{funcdesc}
\begin{funcdesc}{ctime}{secs}
@ -120,18 +130,13 @@ Convert a tuple representing a time as returned by \code{gmtime()} or
\%B & Locale's full month name. \\
\%c & Locale's appropriate date and time representation. \\
\%d & Day of the month as a decimal number [01,31]. \\
\%E & Locale's combined Emperor/Era name and year. \\
\%H & Hour (24-hour clock) as a decimal number [00,23]. \\
\%I & Hour (12-hour clock) as a decimal number [01,12]. \\
\%j & Day of the year as a decimal number [001,366]. \\
\%m & Month as a decimal number [01,12]. \\
\%M & Minute as a decimal number [00,59]. \\
\%n & New-line character. \\
\%N & Locale's Emperor/Era name. \\
\%o & Locale's Emperor/Era year. \\
\%p & Locale's equivalent of either AM or PM. \\
\%S & Second as a decimal number [00,61]. \\
\%t & Tab character. \\
\%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
@ -150,33 +155,13 @@ Convert a tuple representing a time as returned by \code{gmtime()} or
\%\% & \% \\
\end{tabular}
An optional field width and precision specification can immediately
follow the initial \% of a directive in the following order: \\
Additional directives may be supported on certain platforms, but
only the ones listed here have a meaning standardized by ANSI C.
\begin{tabular}{lp{25em}}
[-|0]w & the decimal digit string w specifies a minimum field
width in which the result of the conversion is right-
or left-justified. It is right-justified (with space
padding) by default. If the optional flag `-' is
specified, it is left-justified with space padding on
the right. If the optional flag `0' is specified, it
is right-justified and padded with zeros on the left. \\
.p & the decimal digit string p specifies the minimum number
of digits to appear for the d, H, I, j, m, M, o, S, U,
w, W, y and Y directives, and the maximum number of
characters to be used from the a, A, b, B, c, D, E, F,
h, n, N, p, r, t, T, x, X, z, Z, and % directives. In
the first case, if a directive supplies fewer digits
than specified by the precision, it will be expanded
with leading zeros. In the second case, if a directive
supplies more characters than specified by the
precision, excess characters will truncated on the
right.
\end{tabular}
If no field width or precision is specified for a d, H, I, m, M, S, U,
W, y, or j directive, a default of .2 is used for all but j for which
.3 is used.
On some platforms, an optional field width and precision
specification can immediately follow the initial \% of a
directive in the following order; this is also not portable.
The field width is normally 2 except for \%j where it is 3.
\end{funcdesc}

49
Doc/libtime.tex
View File

@ -32,6 +32,14 @@ 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 \code{time()} and \code{sleep()}
is better than their UNIX equivalents: times are expressed as floating
point numbers, \code{time()} returns the most accurate time available
(using UNIX \code{gettimeofday()} where available), and \code{sleep()}
will accept a time with a nonzero fraction (UNIX \code{select()} is
used to implement this, where available).
\item
The time tuple as returned by \code{gmtime()} and \code{localtime()},
or as accpted by \code{mktime()} is a tuple of 9
@ -68,7 +76,9 @@ the same name, there is no trailing newline.
\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'', depends on that of the C function of the same name.
of ``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 Python
or timing algorithms.
\end{funcdesc}
\begin{funcdesc}{ctime}{secs}
@ -120,18 +130,13 @@ Convert a tuple representing a time as returned by \code{gmtime()} or
\%B & Locale's full month name. \\
\%c & Locale's appropriate date and time representation. \\
\%d & Day of the month as a decimal number [01,31]. \\
\%E & Locale's combined Emperor/Era name and year. \\
\%H & Hour (24-hour clock) as a decimal number [00,23]. \\
\%I & Hour (12-hour clock) as a decimal number [01,12]. \\
\%j & Day of the year as a decimal number [001,366]. \\
\%m & Month as a decimal number [01,12]. \\
\%M & Minute as a decimal number [00,59]. \\
\%n & New-line character. \\
\%N & Locale's Emperor/Era name. \\
\%o & Locale's Emperor/Era year. \\
\%p & Locale's equivalent of either AM or PM. \\
\%S & Second as a decimal number [00,61]. \\
\%t & Tab character. \\
\%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
@ -150,33 +155,13 @@ Convert a tuple representing a time as returned by \code{gmtime()} or
\%\% & \% \\
\end{tabular}
An optional field width and precision specification can immediately
follow the initial \% of a directive in the following order: \\
Additional directives may be supported on certain platforms, but
only the ones listed here have a meaning standardized by ANSI C.
\begin{tabular}{lp{25em}}
[-|0]w & the decimal digit string w specifies a minimum field
width in which the result of the conversion is right-
or left-justified. It is right-justified (with space
padding) by default. If the optional flag `-' is
specified, it is left-justified with space padding on
the right. If the optional flag `0' is specified, it
is right-justified and padded with zeros on the left. \\
.p & the decimal digit string p specifies the minimum number
of digits to appear for the d, H, I, j, m, M, o, S, U,
w, W, y and Y directives, and the maximum number of
characters to be used from the a, A, b, B, c, D, E, F,
h, n, N, p, r, t, T, x, X, z, Z, and % directives. In
the first case, if a directive supplies fewer digits
than specified by the precision, it will be expanded
with leading zeros. In the second case, if a directive
supplies more characters than specified by the
precision, excess characters will truncated on the
right.
\end{tabular}
If no field width or precision is specified for a d, H, I, m, M, S, U,
W, y, or j directive, a default of .2 is used for all but j for which
.3 is used.
On some platforms, an optional field width and precision
specification can immediately follow the initial \% of a
directive in the following order; this is also not portable.
The field width is normally 2 except for \%j where it is 3.
\end{funcdesc}