1 \section{\module{time
} ---
2 Time access and conversions
}
4 \declaremodule{builtin
}{time
}
5 \modulesynopsis{Time access and conversions.
}
8 This module provides various time-related functions.
9 It is always available, but not all functions are available
12 An explanation of some terminology and conventions is in order.
17 The
\dfn{epoch
}\index{epoch
} is the point where the time starts. On
18 January
1st of that year, at
0 hours, the ``time since the epoch'' is
19 zero. For
\UNIX{}, the epoch is
1970. To find out what the epoch is,
20 look at
\code{gmtime(
0)
}.
23 The functions in this module do not handle dates and times before the
24 epoch or far in the future. The cut-off point in the future is
25 determined by the C library; for
\UNIX{}, it is typically in
26 2038\index{Year
2038}.
29 \strong{Year
2000 (Y2K) issues
}:
\index{Year
2000}\index{Y2K
} Python
30 depends on the platform's C library, which generally doesn't have year
31 2000 issues, since all dates and times are represented internally as
32 seconds since the epoch. Functions accepting a time tuple (see below)
33 generally require a
4-digit year. For backward compatibility,
2-digit
34 years are supported if the module variable
\code{accept2dyear
} is a
35 non-zero integer; this variable is initialized to
\code{1} unless the
36 environment variable
\envvar{PYTHONY2K
} is set to a non-empty string,
37 in which case it is initialized to
\code{0}. Thus, you can set
38 \envvar{PYTHONY2K
} to a non-empty string in the environment to require
4-digit
39 years for all year input. When
2-digit years are accepted, they are
40 converted according to the
\POSIX{} or X/Open standard: values
69-
99
41 are mapped to
1969-
1999, and values
0--
68 are mapped to
2000--
2068.
42 Values
100--
1899 are always illegal. Note that this is new as of
43 Python
1.5.2(a2); earlier versions, up to Python
1.5.1 and
1.5.2a1,
44 would add
1900 to year values below
1900.
47 UTC
\index{UTC
} is Coordinated Universal Time
\index{Coordinated
48 Universal Time
} (formerly known as Greenwich Mean
49 Time,
\index{Greenwich Mean Time
} or GMT). The acronym UTC is not a
50 mistake but a compromise between English and French.
53 DST is Daylight Saving Time,
\index{Daylight Saving Time
} an adjustment
54 of the timezone by (usually) one hour during part of the year. DST
55 rules are magic (determined by local law) and can change from year to
56 year. The C library has a table containing the local rules (often it
57 is read from a system file for flexibility) and is the only source of
58 True Wisdom in this respect.
61 The precision of the various real-time functions may be less than
62 suggested by the units in which their value or argument is expressed.
63 E.g.\ on most
\UNIX{} systems, the clock ``ticks'' only
50 or
100 times a
64 second, and on the Mac, times are only accurate to whole seconds.
67 On the other hand, the precision of
\function{time()
} and
68 \function{sleep()
} is better than their
\UNIX{} equivalents: times are
69 expressed as floating point numbers,
\function{time()
} returns the
70 most accurate time available (using
\UNIX{} \cfunction{gettimeofday()
}
71 where available), and
\function{sleep()
} will accept a time with a
72 nonzero fraction (
\UNIX{} \cfunction{select()
} is used to implement
73 this, where available).
77 The time tuple as returned by
\function{gmtime()
},
78 \function{localtime()
}, and
\function{strptime()
}, and accepted by
79 \function{asctime()
},
\function{mktime()
} and
\function{strftime()
},
80 is a tuple of
9 integers:
82 \begin{tableiii
}{r|l|l
}{textrm
}{Index
}{Field
}{Values
}
83 \lineiii{0}{year
}{(e.g.\
1993)
}
84 \lineiii{1}{month
}{range
[1,
12]}
85 \lineiii{2}{day
}{range
[1,
31]}
86 \lineiii{3}{hour
}{range
[0,
23]}
87 \lineiii{4}{minute
}{range
[0,
59]}
88 \lineiii{5}{second
}{range
[0,
61]; see
\strong{(
1)
} in
\function{strftime()
} description
}
89 \lineiii{6}{weekday
}{range
[0,
6], Monday is
0}
90 \lineiii{7}{Julian day
}{range
[1,
366]}
91 \lineiii{8}{daylight savings flag
}{0,
1 or -
1; see below
}
94 Note that unlike the C structure, the month value is a
95 range of
1-
12, not
0-
11. A year value will be handled as described
96 under ``Year
2000 (Y2K) issues'' above. A
\code{-
1} argument as
97 daylight savings flag, passed to
\function{mktime()
} will usually
98 result in the correct daylight savings state to be filled in.
102 The module defines the following functions and data items:
105 \begin{datadesc
}{accept2dyear
}
106 Boolean value indicating whether two-digit year values will be
107 accepted. This is true by default, but will be set to false if the
108 environment variable
\envvar{PYTHONY2K
} has been set to a non-empty
109 string. It may also be modified at run time.
112 \begin{datadesc
}{altzone
}
113 The offset of the local DST timezone, in seconds west of UTC, if one
114 is defined. This is negative if the local DST timezone is east of UTC
115 (as in Western Europe, including the UK). Only use this if
116 \code{daylight
} is nonzero.
119 \begin{funcdesc
}{asctime
}{\optional{tuple
}}
120 Convert a tuple representing a time as returned by
\function{gmtime()
}
121 or
\function{localtime()
} to a
24-character string of the following form:
122 \code{'Sun Jun
20 23:
21:
05 1993'
}. If
\var{tuple
} is not provided, the
123 current time as returned by
\function{localtime()
} is used. Note: unlike
124 the C function of the same name, there is no trailing newline.
125 \versionchanged[Allowed
\var{tuple
} to be omitted
]{2.1}
128 \begin{funcdesc
}{clock
}{}
129 Return the current CPU time as a floating point number expressed in
130 seconds. The precision, and in fact the very definition of the meaning
131 of ``CPU time''
\index{CPU time
}, depends on that of the C function
132 of the same name, but in any case, this is the function to use for
133 benchmarking
\index{benchmarking
} Python or timing algorithms.
136 \begin{funcdesc
}{ctime
}{\optional{secs
}}
137 Convert a time expressed in seconds since the epoch to a string
138 representing local time. If
\var{secs
} is not provided, the current time
139 as returned by
\function{time()
} is used.
\code{ctime(
\var{secs
})
}
140 is equivalent to
\code{asctime(localtime(
\var{secs
}))
}.
141 \versionchanged[Allowed
\var{secs
} to be omitted
]{2.1}
144 \begin{datadesc
}{daylight
}
145 Nonzero if a DST timezone is defined.
148 \begin{funcdesc
}{gmtime
}{\optional{secs
}}
149 Convert a time expressed in seconds since the epoch to a time tuple
150 in UTC in which the dst flag is always zero. If
\var{secs
} is not
151 provided, the current time as returned by
\function{time()
} is used.
152 Fractions of a second are ignored. See above for a description of the
154 \versionchanged[Allowed
\var{secs
} to be omitted
]{2.1}
157 \begin{funcdesc
}{localtime
}{\optional{secs
}}
158 Like
\function{gmtime()
} but converts to local time. The dst flag is
159 set to
\code{1} when DST applies to the given time.
160 \versionchanged[Allowed
\var{secs
} to be omitted
]{2.1}
163 \begin{funcdesc
}{mktime
}{tuple
}
164 This is the inverse function of
\function{localtime()
}. Its argument
165 is the full
9-tuple (since the dst flag is needed; use
\code{-
1} as
166 the dst flag if it is unknown) which expresses the time in
167 \emph{local
} time, not UTC. It returns a floating point number, for
168 compatibility with
\function{time()
}. If the input value cannot be
169 represented as a valid time,
\exception{OverflowError
} is raised.
172 \begin{funcdesc
}{sleep
}{secs
}
173 Suspend execution for the given number of seconds. The argument may
174 be a floating point number to indicate a more precise sleep time.
175 The actual suspension time may be less than that requested because any
176 caught signal will terminate the
\function{sleep()
} following
177 execution of that signal's catching routine. Also, the suspension
178 time may be longer than requested by an arbitrary amount because of
179 the scheduling of other activity in the system.
182 \begin{funcdesc
}{strftime
}{format
\optional{, tuple
}}
183 Convert a tuple representing a time as returned by
\function{gmtime()
}
184 or
\function{localtime()
} to a string as specified by the
\var{format
}
185 argument. If
\var{tuple
} is not provided, the current time as returned by
186 \function{localtime()
} is used.
\var{format
} must be a string.
187 \versionchanged[Allowed
\var{tuple
} to be omitted
]{2.1}
189 The following directives can be embedded in the
\var{format
} string.
190 They are shown without the optional field width and precision
191 specification, and are replaced by the indicated characters in the
192 \function{strftime()
} result:
194 \begin{tableiii
}{c|p
{24em
}|c
}{code
}{Directive
}{Meaning
}{Notes
}
195 \lineiii{\%a
}{Locale's abbreviated weekday name.
}{}
196 \lineiii{\%A
}{Locale's full weekday name.
}{}
197 \lineiii{\%b
}{Locale's abbreviated month name.
}{}
198 \lineiii{\%B
}{Locale's full month name.
}{}
199 \lineiii{\%c
}{Locale's appropriate date and time representation.
}{}
200 \lineiii{\%d
}{Day of the month as a decimal number
[01,
31].
}{}
201 \lineiii{\%H
}{Hour (
24-hour clock) as a decimal number
[00,
23].
}{}
202 \lineiii{\%I
}{Hour (
12-hour clock) as a decimal number
[01,
12].
}{}
203 \lineiii{\%j
}{Day of the year as a decimal number
[001,
366].
}{}
204 \lineiii{\%m
}{Month as a decimal number
[01,
12].
}{}
205 \lineiii{\%M
}{Minute as a decimal number
[00,
59].
}{}
206 \lineiii{\%p
}{Locale's equivalent of either AM or PM.
}{}
207 \lineiii{\%S
}{Second as a decimal number
[00,
61].
}{(
1)
}
208 \lineiii{\%U
}{Week number of the year (Sunday as the first day of the
209 week) as a decimal number
[00,
53]. All days in a new year
210 preceding the first Sunday are considered to be in week
0.
}{}
211 \lineiii{\%w
}{Weekday as a decimal number
[0(Sunday),
6].
}{}
212 \lineiii{\%W
}{Week number of the year (Monday as the first day of the
213 week) as a decimal number
[00,
53]. All days in a new year
214 preceding the first Sunday are considered to be in week
0.
}{}
215 \lineiii{\%x
}{Locale's appropriate date representation.
}{}
216 \lineiii{\%X
}{Locale's appropriate time representation.
}{}
217 \lineiii{\%y
}{Year without century as a decimal number
[00,
99].
}{}
218 \lineiii{\%Y
}{Year with century as a decimal number.
}{}
219 \lineiii{\%Z
}{Time zone name (or by no characters if no time zone exists).
}{}
220 \lineiii{\%\%
}{A literal
\character{\%
} character.
}{}
228 The range really is
\code{0} to
\code{61}; this accounts for leap
229 seconds and the (very rare) double leap seconds.
232 Here is an example, a format for dates compatible with that specified
233 in the
\rfc{822} Internet email standard.
234 \footnote{The use of \%Z is now
235 deprecated, but the \%z escape that expands to the preferred
236 hour/minute offset is not supported by all ANSI C libraries. Also,
237 a strict reading of the original
1982 \rfc{822} standard calls for
238 a two-digit year (\%y rather than \%Y), but practice moved to
239 4-digit years long before the year
2000.
}
242 >>> from time import *
243 >>> strftime("
%a, %d %b %Y %H:%M:%S %Z", localtime())
244 'Sat,
27 Jan
2001 05:
15:
05 EST'
248 Additional directives may be supported on certain platforms, but
249 only the ones listed here have a meaning standardized by ANSI C.
251 On some platforms, an optional field width and precision
252 specification can immediately follow the initial
\character{\%
} of a
253 directive in the following order; this is also not portable.
254 The field width is normally
2 except for
\code{\%j
} where it is
3.
257 \begin{funcdesc
}{strptime
}{string
\optional{, format
}}
258 Parse a string representing a time according to a format. The return
259 value is a tuple as returned by
\function{gmtime()
} or
260 \function{localtime()
}. The
\var{format
} parameter uses the same
261 directives as those used by
\function{strftime()
}; it defaults to
262 \code{"\%a \%b \%d \%H:\%M:\%S \%Y"
} which matches the formatting
263 returned by
\function{ctime()
}. The same platform caveats apply; see
264 the local
\UNIX{} documentation for restrictions or additional
265 supported directives. If
\var{string
} cannot be parsed according to
266 \var{format
},
\exception{ValueError
} is raised. Values which are not
267 provided as part of the input string are filled in with default
268 values; the specific values are platform-dependent as the XPG standard
269 does not provide sufficient information to constrain the result.
271 \strong{Note:
} This function relies entirely on the underlying
272 platform's C library for the date parsing, and some of these libraries
273 are buggy. There's nothing to be done about this short of a new,
274 portable implementation of
\cfunction{strptime()
}.
276 Availability: Most modern
\UNIX{} systems.
279 \begin{funcdesc
}{time
}{}
280 Return the time as a floating point number expressed in seconds since
281 the epoch, in UTC. Note that even though the time is always returned
282 as a floating point number, not all systems provide time with a better
283 precision than
1 second.
286 \begin{datadesc
}{timezone
}
287 The offset of the local (non-DST) timezone, in seconds west of UTC
288 (i.e. negative in most of Western Europe, positive in the US, zero in
292 \begin{datadesc
}{tzname
}
293 A tuple of two strings: the first is the name of the local non-DST
294 timezone, the second is the name of the local DST timezone. If no DST
295 timezone is defined, the second string should not be used.
300 \seemodule{locale
}{Internationalization services. The locale
301 settings can affect the return values for some of
302 the functions in the
\module{time
} module.
}
