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
\class{struct_time
}
33 (see below) generally require a
4-digit year. For backward
34 compatibility,
2-digit years are supported if the module variable
35 \code{accept2dyear
} is a non-zero integer; this variable is
36 initialized to
\code{1} unless the environment variable
37 \envvar{PYTHONY2K
} is set to a non-empty string, in which case it is
38 initialized to
\code{0}. Thus, you can set
39 \envvar{PYTHONY2K
} to a non-empty string in the environment to require
4-digit
40 years for all year input. When
2-digit years are accepted, they are
41 converted according to the
\POSIX{} or X/Open standard: values
69-
99
42 are mapped to
1969-
1999, and values
0--
68 are mapped to
2000--
2068.
43 Values
100--
1899 are always illegal. Note that this is new as of
44 Python
1.5.2(a2); earlier versions, up to Python
1.5.1 and
1.5.2a1,
45 would add
1900 to year values below
1900.
48 UTC
\index{UTC
} is Coordinated Universal Time
\index{Coordinated
49 Universal Time
} (formerly known as Greenwich Mean
50 Time,
\index{Greenwich Mean Time
} or GMT). The acronym UTC is not a
51 mistake but a compromise between English and French.
54 DST is Daylight Saving Time,
\index{Daylight Saving Time
} an adjustment
55 of the timezone by (usually) one hour during part of the year. DST
56 rules are magic (determined by local law) and can change from year to
57 year. The C library has a table containing the local rules (often it
58 is read from a system file for flexibility) and is the only source of
59 True Wisdom in this respect.
62 The precision of the various real-time functions may be less than
63 suggested by the units in which their value or argument is expressed.
64 E.g.\ on most
\UNIX{} systems, the clock ``ticks'' only
50 or
100 times a
65 second, and on the Mac, times are only accurate to whole seconds.
68 On the other hand, the precision of
\function{time()
} and
69 \function{sleep()
} is better than their
\UNIX{} equivalents: times are
70 expressed as floating point numbers,
\function{time()
} returns the
71 most accurate time available (using
\UNIX{} \cfunction{gettimeofday()
}
72 where available), and
\function{sleep()
} will accept a time with a
73 nonzero fraction (
\UNIX{} \cfunction{select()
} is used to implement
74 this, where available).
77 The time value 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 sequence of
9 integers. The return values of
\function{gmtime()
},
81 \function{localtime()
}, and
\function{strptime()
} also offer attribute
82 names for individual fields.
84 \begin{tableiii
}{c|l|l
}{textrm
}{Index
}{Attribute
}{Values
}
85 \lineiii{0}{\member{tm_year
}}{(for example,
1993)
}
86 \lineiii{1}{\member{tm_mon
}}{range
[1,
12]}
87 \lineiii{2}{\member{tm_mday
}}{range
[1,
31]}
88 \lineiii{3}{\member{tm_hour
}}{range
[0,
23]}
89 \lineiii{4}{\member{tm_min
}}{range
[0,
59]}
90 \lineiii{5}{\member{tm_sec
}}{range
[0,
61]; see
\strong{(
1)
} in
\function{strftime()
} description
}
91 \lineiii{6}{\member{tm_wday
}}{range
[0,
6], Monday is
0}
92 \lineiii{7}{\member{tm_yday
}}{range
[1,
366]}
93 \lineiii{8}{\member{tm_isdst
}}{0,
1 or -
1; see below
}
96 Note that unlike the C structure, the month value is a
97 range of
1-
12, not
0-
11. A year value will be handled as described
98 under ``Year
2000 (Y2K) issues'' above. A
\code{-
1} argument as the
99 daylight savings flag, passed to
\function{mktime()
} will usually
100 result in the correct daylight savings state to be filled in.
102 When a tuple with an incorrect length is passed to a function
103 expecting a
\class{struct_time
}, or having elements of the wrong type, a
104 \exception{TypeError
} is raised.
106 \versionchanged[The time value sequence was changed from a tuple to a
107 \class{struct_time
}, with the addition of attribute names
111 The module defines the following functions and data items:
114 \begin{datadesc
}{accept2dyear
}
115 Boolean value indicating whether two-digit year values will be
116 accepted. This is true by default, but will be set to false if the
117 environment variable
\envvar{PYTHONY2K
} has been set to a non-empty
118 string. It may also be modified at run time.
121 \begin{datadesc
}{altzone
}
122 The offset of the local DST timezone, in seconds west of UTC, if one
123 is defined. This is negative if the local DST timezone is east of UTC
124 (as in Western Europe, including the UK). Only use this if
125 \code{daylight
} is nonzero.
128 \begin{funcdesc
}{asctime
}{\optional{t
}}
129 Convert a tuple or
\class{struct_time
} representing a time as returned
130 by
\function{gmtime()
}
131 or
\function{localtime()
} to a
24-character string of the following form:
132 \code{'Sun Jun
20 23:
21:
05 1993'
}. If
\var{t
} is not provided, the
133 current time as returned by
\function{localtime()
} is used.
134 Locale information is not used by
\function{asctime()
}.
135 \note{Unlike the C function of the same name, there is no trailing
137 \versionchanged[Allowed
\var{t
} to be omitted
]{2.1}
140 \begin{funcdesc
}{clock
}{}
142 the current processor time as a floating point number expressed in
143 seconds. The precision, and in fact the very definition of the meaning
144 of ``processor time''
\index{CPU time
}\index{processor time
}, depends
145 on that of the C function of the same name, but in any case, this is
146 the function to use for benchmarking
\index{benchmarking
} Python or
149 On Windows, this function returns wall-clock seconds elapsed since the
150 first call to this function, as a floating point number,
151 based on the Win32 function
\cfunction{QueryPerformanceCounter()
}.
152 The resolution is typically better than one microsecond.
155 \begin{funcdesc
}{ctime
}{\optional{secs
}}
156 Convert a time expressed in seconds since the epoch to a string
157 representing local time. If
\var{secs
} is not provided, the current time
158 as returned by
\function{time()
} is used.
\code{ctime(
\var{secs
})
}
159 is equivalent to
\code{asctime(localtime(
\var{secs
}))
}.
160 Locale information is not used by
\function{ctime()
}.
161 \versionchanged[Allowed
\var{secs
} to be omitted
]{2.1}
164 \begin{datadesc
}{daylight
}
165 Nonzero if a DST timezone is defined.
168 \begin{funcdesc
}{gmtime
}{\optional{secs
}}
169 Convert a time expressed in seconds since the epoch to a
\class{struct_time
}
170 in UTC in which the dst flag is always zero. If
\var{secs
} is not
171 provided, the current time as returned by
\function{time()
} is used.
172 Fractions of a second are ignored. See above for a description of the
173 \class{struct_time
} object.
174 \versionchanged[Allowed
\var{secs
} to be omitted
]{2.1}
177 \begin{funcdesc
}{localtime
}{\optional{secs
}}
178 Like
\function{gmtime()
} but converts to local time. The dst flag is
179 set to
\code{1} when DST applies to the given time.
180 \versionchanged[Allowed
\var{secs
} to be omitted
]{2.1}
183 \begin{funcdesc
}{mktime
}{t
}
184 This is the inverse function of
\function{localtime()
}. Its argument
185 is the
\class{struct_time
} or full
9-tuple (since the dst flag is
186 needed; use
\code{-
1} as the dst flag if it is unknown) which
187 expresses the time in
188 \emph{local
} time, not UTC. It returns a floating point number, for
189 compatibility with
\function{time()
}. If the input value cannot be
190 represented as a valid time, either
\exception{OverflowError
} or
191 \exception{ValueError
} will be raised (which depends on whether the
192 invalid value is caught by Python or the underlying C libraries). The
193 earliest date for which it can generate a time is platform-dependent.
196 \begin{funcdesc
}{sleep
}{secs
}
197 Suspend execution for the given number of seconds. The argument may
198 be a floating point number to indicate a more precise sleep time.
199 The actual suspension time may be less than that requested because any
200 caught signal will terminate the
\function{sleep()
} following
201 execution of that signal's catching routine. Also, the suspension
202 time may be longer than requested by an arbitrary amount because of
203 the scheduling of other activity in the system.
206 \begin{funcdesc
}{strftime
}{format
\optional{, t
}}
207 Convert a tuple or
\class{struct_time
} representing a time as returned
208 by
\function{gmtime()
} or
\function{localtime()
} to a string as
209 specified by the
\var{format
} argument. If
\var{t
} is not
210 provided, the current time as returned by
\function{localtime()
} is
211 used.
\var{format
} must be a string.
212 \versionchanged[Allowed
\var{t
} to be omitted
]{2.1}
214 The following directives can be embedded in the
\var{format
} string.
215 They are shown without the optional field width and precision
216 specification, and are replaced by the indicated characters in the
217 \function{strftime()
} result:
219 \begin{tableiii
}{c|p
{24em
}|c
}{code
}{Directive
}{Meaning
}{Notes
}
220 \lineiii{\%a
}{Locale's abbreviated weekday name.
}{}
221 \lineiii{\%A
}{Locale's full weekday name.
}{}
222 \lineiii{\%b
}{Locale's abbreviated month name.
}{}
223 \lineiii{\%B
}{Locale's full month name.
}{}
224 \lineiii{\%c
}{Locale's appropriate date and time representation.
}{}
225 \lineiii{\%d
}{Day of the month as a decimal number
[01,
31].
}{}
226 \lineiii{\%H
}{Hour (
24-hour clock) as a decimal number
[00,
23].
}{}
227 \lineiii{\%I
}{Hour (
12-hour clock) as a decimal number
[01,
12].
}{}
228 \lineiii{\%j
}{Day of the year as a decimal number
[001,
366].
}{}
229 \lineiii{\%m
}{Month as a decimal number
[01,
12].
}{}
230 \lineiii{\%M
}{Minute as a decimal number
[00,
59].
}{}
231 \lineiii{\%p
}{Locale's equivalent of either AM or PM.
}{}
232 \lineiii{\%S
}{Second as a decimal number
[00,
61].
}{(
1)
}
233 \lineiii{\%U
}{Week number of the year (Sunday as the first day of the
234 week) as a decimal number
[00,
53]. All days in a new year
235 preceding the first Sunday are considered to be in week
0.
}{}
236 \lineiii{\%w
}{Weekday as a decimal number
[0(Sunday),
6].
}{}
237 \lineiii{\%W
}{Week number of the year (Monday as the first day of the
238 week) as a decimal number
[00,
53]. All days in a new year
239 preceding the first Monday are considered to be in week
0.
}{}
240 \lineiii{\%x
}{Locale's appropriate date representation.
}{}
241 \lineiii{\%X
}{Locale's appropriate time representation.
}{}
242 \lineiii{\%y
}{Year without century as a decimal number
[00,
99].
}{}
243 \lineiii{\%Y
}{Year with century as a decimal number.
}{}
244 \lineiii{\%Z
}{Time zone name (no characters if no time zone exists).
}{}
245 \lineiii{\%\%
}{A literal
\character{\%
} character.
}{}
253 The range really is
\code{0} to
\code{61}; this accounts for leap
254 seconds and the (very rare) double leap seconds.
257 Here is an example, a format for dates compatible with that specified
258 in the
\rfc{2822} Internet email standard.
259 \footnote{The use of
\code{\%Z
} is now
260 deprecated, but the
\code{\%z
} escape that expands to the preferred
261 hour/minute offset is not supported by all ANSI C libraries. Also,
262 a strict reading of the original
1982 \rfc{822} standard calls for
263 a two-digit year (\%y rather than \%Y), but practice moved to
264 4-digit years long before the year
2000. The
4-digit year has
265 been mandated by
\rfc{2822}, which obsoletes
\rfc{822}.
}
268 >>> from time import gmtime, strftime
269 >>> strftime("
%a, %d %b %Y %H:%M:%S +0000", gmtime())
270 'Thu,
28 Jun
2001 14:
17:
15 +
0000'
273 Additional directives may be supported on certain platforms, but
274 only the ones listed here have a meaning standardized by ANSI C.
276 On some platforms, an optional field width and precision
277 specification can immediately follow the initial
\character{\%
} of a
278 directive in the following order; this is also not portable.
279 The field width is normally
2 except for
\code{\%j
} where it is
3.
282 \begin{funcdesc
}{strptime
}{string
\optional{, format
}}
283 Parse a string representing a time according to a format. The return
284 value is a
\class{struct_time
} as returned by
\function{gmtime()
} or
285 \function{localtime()
}. The
\var{format
} parameter uses the same
286 directives as those used by
\function{strftime()
}; it defaults to
287 \code{"\%a \%b \%d \%H:\%M:\%S \%Y"
} which matches the formatting
288 returned by
\function{ctime()
}. The same platform caveats apply; see
289 the local
\UNIX{} documentation for restrictions or additional
290 supported directives. If
\var{string
} cannot be parsed according to
291 \var{format
},
\exception{ValueError
} is raised. Values which are not
292 provided as part of the input string are filled in with default
293 values; the specific values are platform-dependent as the XPG standard
294 does not provide sufficient information to constrain the result.
297 \begin{datadesc
}{struct_time
}
298 The type of the time value sequence returned by
\function{gmtime()
},
299 \function{localtime()
}, and
\function{strptime()
}.
303 \begin{funcdesc
}{time
}{}
304 Return the time as a floating point number expressed in seconds since
305 the epoch, in UTC. Note that even though the time is always returned
306 as a floating point number, not all systems provide time with a better
307 precision than
1 second. While this function normally returns
308 non-decreasing values, it can return a lower value than a previous
309 call if the system clock has been set back between the two calls.
312 \begin{datadesc
}{timezone
}
313 The offset of the local (non-DST) timezone, in seconds west of UTC
314 (negative in most of Western Europe, positive in the US, zero in the
318 \begin{datadesc
}{tzname
}
319 A tuple of two strings: the first is the name of the local non-DST
320 timezone, the second is the name of the local DST timezone. If no DST
321 timezone is defined, the second string should not be used.
326 \seemodule{locale
}{Internationalization services. The locale
327 settings can affect the return values for some of
328 the functions in the
\module{time
} module.
}
329 \seemodule{calendar
}{General calendar-related functions.
330 \function{timegm()
} is the inverse of
331 \function{gmtime()
} from this module.
}
