1402 lines
53 KiB
TeX
1402 lines
53 KiB
TeX
% XXX what order should the types be discussed in?
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\section{\module{datetime} ---
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Basic date and time types}
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\declaremodule{builtin}{datetime}
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\modulesynopsis{Basic date and time types.}
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\moduleauthor{Tim Peters}{tim@zope.com}
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\sectionauthor{Tim Peters}{tim@zope.com}
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\sectionauthor{A.M. Kuchling}{amk@amk.ca}
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\versionadded{2.3}
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The \module{datetime} module supplies classes for manipulating dates
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and times in both simple and complex ways. While date and time
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arithmetic is supported, the focus of the implementation is on
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efficient member extraction for output formatting and manipulation.
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There are two kinds of date and time objects: ``naive'' and ``aware''.
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This distinction refers to whether the object has any notion of time
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zone, daylight saving time, or other kind of algorithmic or political
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time adjustment. Whether a naive \class{datetime} object represents
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Coordinated Universal Time (UTC), local time, or time in some other
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timezone is purely up to the program, just like it's up to the program
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whether a particular number represents meters, miles, or mass. Naive
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\class{datetime} objects are easy to understand and to work with, at
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the cost of ignoring some aspects of reality.
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For applications requiring more, \class{datetime} and \class{time}
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objects have an optional time zone information member,
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\member{tzinfo}, that can contain an instance of a subclass of
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the abstract \class{tzinfo} class. These \class{tzinfo} objects
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capture information about the offset from UTC time, the time zone
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name, and whether Daylight Saving Time is in effect. Note that no
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concrete \class{tzinfo} classes are supplied by the \module{datetime}
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module. Supporting timezones at whatever level of detail is required
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is up to the application. The rules for time adjustment across the
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world are more political than rational, and there is no standard
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suitable for every application.
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The \module{datetime} module exports the following constants:
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\begin{datadesc}{MINYEAR}
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The smallest year number allowed in a \class{date} or
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\class{datetime} object. \constant{MINYEAR}
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is \code{1}.
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\end{datadesc}
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\begin{datadesc}{MAXYEAR}
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The largest year number allowed in a \class{date} or \class{datetime}
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object. \constant{MAXYEAR} is \code{9999}.
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\end{datadesc}
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\begin{seealso}
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\seemodule{calendar}{General calendar related functions.}
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\seemodule{time}{Time access and conversions.}
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\end{seealso}
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\subsection{Available Types}
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\begin{classdesc*}{date}
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An idealized naive date, assuming the current Gregorian calendar
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always was, and always will be, in effect.
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Attributes: \member{year}, \member{month}, and \member{day}.
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\end{classdesc*}
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\begin{classdesc*}{time}
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An idealized time, independent of any particular day, assuming
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that every day has exactly 24*60*60 seconds (there is no notion
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of "leap seconds" here).
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Attributes: \member{hour}, \member{minute}, \member{second},
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\member{microsecond}, and \member{tzinfo}.
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\end{classdesc*}
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\begin{classdesc*}{datetime}
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A combination of a date and a time.
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Attributes: \member{year}, \member{month}, \member{day},
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\member{hour}, \member{minute}, \member{second},
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\member{microsecond}, and \member{tzinfo}.
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\end{classdesc*}
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\begin{classdesc*}{timedelta}
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A duration expressing the difference between two \class{date},
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\class{time}, or \class{datetime} instances to microsecond
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resolution.
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\end{classdesc*}
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\begin{classdesc*}{tzinfo}
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An abstract base class for time zone information objects. These
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are used by the \class{datetime} and \class{time} classes to
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provide a customizable notion of time adjustment (for example, to
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account for time zone and/or daylight saving time).
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\end{classdesc*}
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Objects of these types are immutable.
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Objects of the \class{date} type are always naive.
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An object \var{d} of type \class{time} or \class{datetime} may be
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naive or aware. \var{d} is aware if \code{\var{d}.tzinfo} is not
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\code{None} and \code{\var{d}.tzinfo.utcoffset(\var{d})} does not return
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\code{None}. If \code{\var{d}.tzinfo} is \code{None}, or if
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\code{\var{d}.tzinfo} is not \code{None} but
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\code{\var{d}.tzinfo.utcoffset(\var{d})} returns \code{None}, \var{d}
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is naive.
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The distinction between naive and aware doesn't apply to
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\code{timedelta} objects.
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Subclass relationships:
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\begin{verbatim}
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object
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timedelta
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tzinfo
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time
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date
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datetime
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\end{verbatim}
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\subsection{\class{timedelta} Objects \label{datetime-timedelta}}
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A \class{timedelta} object represents a duration, the difference
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between two dates or times.
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\begin{classdesc}{timedelta}{days=0, seconds=0, microseconds=0,
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milliseconds=0, minutes=0, hours=0, weeks=0}
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All arguments are optional. Arguments may be ints, longs, or floats,
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and may be positive or negative.
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Only \var{days}, \var{seconds} and \var{microseconds} are stored
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internally. Arguments are converted to those units:
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\begin{itemize}
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\item A millisecond is converted to 1000 microseconds.
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\item A minute is converted to 60 seconds.
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\item An hour is converted to 3600 seconds.
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\item A week is converted to 7 days.
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\end{itemize}
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and days, seconds and microseconds are then normalized so that the
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representation is unique, with
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\begin{itemize}
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\item \code{0 <= \var{microseconds} < 1000000}
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\item \code{0 <= \var{seconds} < 3600*24} (the number of seconds in one day)
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\item \code{-999999999 <= \var{days} <= 999999999}
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\end{itemize}
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If any argument is a float and there are fractional microseconds,
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the fractional microseconds left over from all arguments are combined
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and their sum is rounded to the nearest microsecond. If no
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argument is a float, the conversion and normalization processes
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are exact (no information is lost).
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If the normalized value of days lies outside the indicated range,
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\exception{OverflowError} is raised.
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Note that normalization of negative values may be surprising at first.
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For example,
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\begin{verbatim}
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>>> d = timedelta(microseconds=-1)
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>>> (d.days, d.seconds, d.microseconds)
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(-1, 86399, 999999)
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\end{verbatim}
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\end{classdesc}
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Class attributes are:
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\begin{memberdesc}{min}
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The most negative \class{timedelta} object,
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\code{timedelta(-999999999)}.
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\end{memberdesc}
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\begin{memberdesc}{max}
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The most positive \class{timedelta} object,
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\code{timedelta(days=999999999, hours=23, minutes=59, seconds=59,
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microseconds=999999)}.
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\end{memberdesc}
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\begin{memberdesc}{resolution}
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The smallest possible difference between non-equal
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\class{timedelta} objects, \code{timedelta(microseconds=1)}.
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\end{memberdesc}
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Note that, because of normalization, \code{timedelta.max} \textgreater
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\code{-timedelta.min}. \code{-timedelta.max} is not representable as
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a \class{timedelta} object.
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Instance attributes (read-only):
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\begin{tableii}{c|l}{code}{Attribute}{Value}
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\lineii{days}{Between -999999999 and 999999999 inclusive}
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\lineii{seconds}{Between 0 and 86399 inclusive}
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\lineii{microseconds}{Between 0 and 999999 inclusive}
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\end{tableii}
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Supported operations:
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% XXX this table is too wide!
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\begin{tableii}{c|l}{code}{Operation}{Result}
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\lineii{\var{t1} = \var{t2} + \var{t3}}
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{Sum of \var{t2} and \var{t3}.
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Afterwards \var{t1}-\var{t2} == \var{t3} and \var{t1}-\var{t3}
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== \var{t2} are true.
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(1)}
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\lineii{\var{t1} = \var{t2} - \var{t3}}
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{Difference of \var{t2} and \var{t3}.
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Afterwards \var{t1} == \var{t2} - \var{t3} and \var{t2} == \var{t1} + \var{t3} are
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true.
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(1)}
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\lineii{\var{t1} = \var{t2} * \var{i} or \var{t1} = \var{i} * \var{t2}}
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{Delta multiplied by an integer or long.
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Afterwards \var{t1} // i == \var{t2} is true,
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provided \code{i != 0}.}
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\lineii{}{In general, \var{t1} * i == \var{t1} * (i-1) + \var{t1} is true.
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(1)}
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\lineii{\var{t1} = \var{t2} // \var{i}}
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{The floor is computed and the remainder (if any) is thrown away.
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(3)}
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\lineii{+\var{t1}}
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{Returns a \class{timedelta} object with the same value.
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(2)}
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\lineii{-\var{t1}}
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{equivalent to \class{timedelta}(-\var{t1.days}, -\var{t1.seconds},
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-\var{t1.microseconds}), and to \var{t1}* -1.
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(1)(4)}
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\lineii{abs(\var{t})}
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{equivalent to +\var{t} when \code{t.days >= 0}, and to
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-\var{t} when \code{t.days < 0}.
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(2)}
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\end{tableii}
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\noindent
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Notes:
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\begin{description}
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\item[(1)]
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This is exact, but may overflow.
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\item[(2)]
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This is exact, and cannot overflow.
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\item[(3)]
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Division by 0 raises \exception{ZeroDivisionError}.
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\item[(4)]
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-\var{timedelta.max} is not representable as a \class{timedelta} object.
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\end{description}
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In addition to the operations listed above \class{timedelta} objects
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support certain additions and subtractions with \class{date} and
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\class{datetime} objects (see below).
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Comparisons of \class{timedelta} objects are supported with the
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\class{timedelta} object representing the smaller duration considered
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to be the smaller timedelta.
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In order to stop mixed-type comparisons from falling back to the
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default comparison by object address, when a \class{timedelta} object is
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compared to an object of a different type, \exception{TypeError} is
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raised unless the comparison is \code{==} or \code{!=}. The latter
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cases return \constant{False} or \constant{True}, respectively.
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\class{timedelta} objects are hashable (usable as dictionary keys),
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support efficient pickling, and in Boolean contexts, a \class{timedelta}
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object is considered to be true if and only if it isn't equal to
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\code{timedelta(0)}.
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\subsection{\class{date} Objects \label{datetime-date}}
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A \class{date} object represents a date (year, month and day) in an idealized
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calendar, the current Gregorian calendar indefinitely extended in both
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directions. January 1 of year 1 is called day number 1, January 2 of year
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1 is called day number 2, and so on. This matches the definition of the
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"proleptic Gregorian" calendar in Dershowitz and Reingold's book
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\citetitle{Calendrical Calculations}, where it's the base calendar for all
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computations. See the book for algorithms for converting between
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proleptic Gregorian ordinals and many other calendar systems.
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\begin{classdesc}{date}{year, month, day}
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All arguments are required. Arguments may be ints or longs, in the
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following ranges:
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\begin{itemize}
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\item \code{MINYEAR <= \var{year} <= MAXYEAR}
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\item \code{1 <= \var{month} <= 12}
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\item \code{1 <= \var{day} <= number of days in the given month and year}
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\end{itemize}
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If an argument outside those ranges is given, \exception{ValueError}
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is raised.
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\end{classdesc}
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Other constructors, all class methods:
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\begin{methoddesc}{today}{}
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Return the current local date. This is equivalent to
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\code{date.fromtimestamp(time.time())}.
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\end{methoddesc}
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\begin{methoddesc}{fromtimestamp}{timestamp}
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Return the local date corresponding to the POSIX timestamp, such
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as is returned by \function{time.time()}. This may raise
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\exception{ValueError}, if the timestamp is out of the range of
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values supported by the platform C \cfunction{localtime()}
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function. It's common for this to be restricted to years from 1970
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through 2038. Note that on non-POSIX systems that include leap
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seconds in their notion of a timestamp, leap seconds are ignored by
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\method{fromtimestamp()}.
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\end{methoddesc}
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\begin{methoddesc}{fromordinal}{ordinal}
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Return the date corresponding to the proleptic Gregorian ordinal,
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where January 1 of year 1 has ordinal 1. \exception{ValueError} is
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raised unless \code{1 <= \var{ordinal} <= date.max.toordinal()}.
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For any date \var{d}, \code{date.fromordinal(\var{d}.toordinal()) ==
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\var{d}}.
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\end{methoddesc}
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Class attributes:
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\begin{memberdesc}{min}
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The earliest representable date, \code{date(MINYEAR, 1, 1)}.
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\end{memberdesc}
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\begin{memberdesc}{max}
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The latest representable date, \code{date(MAXYEAR, 12, 31)}.
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\end{memberdesc}
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\begin{memberdesc}{resolution}
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The smallest possible difference between non-equal date
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objects, \code{timedelta(days=1)}.
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\end{memberdesc}
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Instance attributes (read-only):
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\begin{memberdesc}{year}
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Between \constant{MINYEAR} and \constant{MAXYEAR} inclusive.
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\end{memberdesc}
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\begin{memberdesc}{month}
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Between 1 and 12 inclusive.
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\end{memberdesc}
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\begin{memberdesc}{day}
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Between 1 and the number of days in the given month of the given
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year.
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\end{memberdesc}
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Supported operations:
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% XXX rewrite to be a table
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\begin{tableii}{c|l}{code}{Operation}{Result}
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\lineii{\var{date2} = \var{date1} + \var{timedelta}}
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{\var{date2} is \code{\var{timedelta}.days} days removed from
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\var{date1}. (1)}
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\lineii{\var{date2} = \var{date1} - \var{timedelta}}
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{Computes \var{date2} such that \code{\var{date2} + \var{timedelta}
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== \var{date1}}. (2)}
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\lineii{\var{timedelta} = \var{date1} - \var{date2}}
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{(3)}
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\lineii{\var{date1}<\var{date2}}
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{\var{date1} is considered less than \var{date2} when \var{date1}
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precedes \var{date2} in time. (4)}
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\end{tableii}
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Notes:
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\begin{description}
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\item[(1)]
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\var{date2} is moved forward in time if \code{\var{timedelta}.days
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> 0}, or backward if \code{\var{timedelta}.days < 0}. Afterward
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\code{\var{date2} - \var{date1} == \var{timedelta}.days}.
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\code{\var{timedelta}.seconds} and
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\code{\var{timedelta}.microseconds} are ignored.
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\exception{OverflowError} is raised if \code{\var{date2}.year}
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would be smaller than \constant{MINYEAR} or larger than
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\constant{MAXYEAR}.
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\item[(2)]
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This isn't quite equivalent to date1 +
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(-timedelta), because -timedelta in isolation can overflow in cases
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where date1 - timedelta does not. \code{\var{timedelta}.seconds}
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and \code{\var{timedelta}.microseconds} are ignored.
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\item[(3)]
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This is exact, and cannot overflow. timedelta.seconds and
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timedelta.microseconds are 0, and date2 + timedelta == date1
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after.
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\item[(4)]
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In other words, \code{date1 < date2}
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if and only if \code{\var{date1}.toordinal() <
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\var{date2}.toordinal()}.
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In order to stop comparison from falling back to the default
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scheme of comparing object addresses, date comparison
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normally raises \exception{TypeError} if the other comparand
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isn't also a \class{date} object. However, \code{NotImplemented}
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is returned instead if the other comparand has a
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\method{timetuple} attribute. This hook gives other kinds of
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date objects a chance at implementing mixed-type comparison.
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If not, when a \class{date} object is
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compared to an object of a different type, \exception{TypeError} is
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raised unless the comparison is \code{==} or \code{!=}. The latter
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cases return \constant{False} or \constant{True}, respectively.
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\end{description}
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Dates can be used as dictionary keys. In Boolean contexts, all
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\class{date} objects are considered to be true.
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Instance methods:
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\begin{methoddesc}{replace}{year, month, day}
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Return a date with the same value, except for those members given
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new values by whichever keyword arguments are specified. For
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example, if \code{d == date(2002, 12, 31)}, then
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\code{d.replace(day=26) == date(2000, 12, 26)}.
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\end{methoddesc}
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\begin{methoddesc}{timetuple}{}
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Return a \class{time.struct_time} such as returned by
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\function{time.localtime()}. The hours, minutes and seconds are
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0, and the DST flag is -1.
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\code{\var{d}.timetuple()} is equivalent to
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\code{time.struct_time((\var{d}.year, \var{d}.month, \var{d}.day,
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0, 0, 0,
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\var{d}.weekday(),
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\var{d}.toordinal() - date(\var{d}.year, 1, 1).toordinal() + 1,
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-1))}
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\end{methoddesc}
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\begin{methoddesc}{toordinal}{}
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Return the proleptic Gregorian ordinal of the date, where January 1
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of year 1 has ordinal 1. For any \class{date} object \var{d},
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\code{date.fromordinal(\var{d}.toordinal()) == \var{d}}.
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\end{methoddesc}
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\begin{methoddesc}{weekday}{}
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Return the day of the week as an integer, where Monday is 0 and
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Sunday is 6. For example, \code{date(2002, 12, 4).weekday() == 2}, a
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Wednesday.
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See also \method{isoweekday()}.
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\end{methoddesc}
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\begin{methoddesc}{isoweekday}{}
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Return the day of the week as an integer, where Monday is 1 and
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Sunday is 7. For example, \code{date(2002, 12, 4).isoweekday() == 3}, a
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Wednesday.
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See also \method{weekday()}, \method{isocalendar()}.
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\end{methoddesc}
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\begin{methoddesc}{isocalendar}{}
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Return a 3-tuple, (ISO year, ISO week number, ISO weekday).
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The ISO calendar is a widely used variant of the Gregorian calendar.
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See \url{http://www.phys.uu.nl/~vgent/calendar/isocalendar.htm}
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for a good explanation.
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|
|
The ISO year consists of 52 or 53 full weeks, and where a week starts
|
|
on a Monday and ends on a Sunday. The first week of an ISO year is
|
|
the first (Gregorian) calendar week of a year containing a Thursday.
|
|
This is called week number 1, and the ISO year of that Thursday is
|
|
the same as its Gregorian year.
|
|
|
|
For example, 2004 begins on a Thursday, so the first week of ISO
|
|
year 2004 begins on Monday, 29 Dec 2003 and ends on Sunday, 4 Jan
|
|
2004, so that
|
|
\code{date(2003, 12, 29).isocalendar() == (2004, 1, 1)}
|
|
and
|
|
\code{date(2004, 1, 4).isocalendar() == (2004, 1, 7)}.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{isoformat}{}
|
|
Return a string representing the date in ISO 8601 format,
|
|
'YYYY-MM-DD'. For example,
|
|
\code{date(2002, 12, 4).isoformat() == '2002-12-04'}.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{__str__}{}
|
|
For a date \var{d}, \code{str(\var{d})} is equivalent to
|
|
\code{\var{d}.isoformat()}.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{ctime}{}
|
|
Return a string representing the date, for example
|
|
date(2002, 12, 4).ctime() == 'Wed Dec 4 00:00:00 2002'.
|
|
\code{\var{d}.ctime()} is equivalent to
|
|
\code{time.ctime(time.mktime(\var{d}.timetuple()))}
|
|
on platforms where the native C \cfunction{ctime()} function
|
|
(which \function{time.ctime()} invokes, but which
|
|
\method{date.ctime()} does not invoke) conforms to the C standard.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{strftime}{format}
|
|
Return a string representing the date, controlled by an explicit
|
|
format string. Format codes referring to hours, minutes or seconds
|
|
will see 0 values.
|
|
See the section on \method{strftime()} behavior.
|
|
\end{methoddesc}
|
|
|
|
|
|
\subsection{\class{datetime} Objects \label{datetime-datetime}}
|
|
|
|
A \class{datetime} object is a single object containing all the
|
|
information from a \class{date} object and a \class{time} object. Like a
|
|
\class{date} object, \class{datetime} assumes the current Gregorian
|
|
calendar extended in both directions; like a time object,
|
|
\class{datetime} assumes there are exactly 3600*24 seconds in every
|
|
day.
|
|
|
|
Constructor:
|
|
|
|
\begin{classdesc}{datetime}{year, month, day,
|
|
hour=0, minute=0, second=0, microsecond=0,
|
|
tzinfo=None}
|
|
The year, month and day arguments are required. \var{tzinfo} may
|
|
be \code{None}, or an instance of a \class{tzinfo} subclass. The
|
|
remaining arguments may be ints or longs, in the following ranges:
|
|
|
|
\begin{itemize}
|
|
\item \code{MINYEAR <= \var{year} <= MAXYEAR}
|
|
\item \code{1 <= \var{month} <= 12}
|
|
\item \code{1 <= \var{day} <= number of days in the given month and year}
|
|
\item \code{0 <= \var{hour} < 24}
|
|
\item \code{0 <= \var{minute} < 60}
|
|
\item \code{0 <= \var{second} < 60}
|
|
\item \code{0 <= \var{microsecond} < 1000000}
|
|
\end{itemize}
|
|
|
|
If an argument outside those ranges is given,
|
|
\exception{ValueError} is raised.
|
|
\end{classdesc}
|
|
|
|
Other constructors, all class methods:
|
|
|
|
\begin{methoddesc}{today}{}
|
|
Return the current local datetime, with \member{tzinfo} \code{None}.
|
|
This is equivalent to
|
|
\code{datetime.fromtimestamp(time.time())}.
|
|
See also \method{now()}, \method{fromtimestamp()}.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{now(tz=None)}{}
|
|
Return the current local date and time. If optional argument
|
|
\var{tz} is \code{None} or not specified, this is like
|
|
\method{today()}, but, if possible, supplies more precision than can
|
|
be gotten from going through a \function{time.time()} timestamp (for
|
|
example, this may be possible on platforms supplying the C
|
|
\cfunction{gettimeofday()} function).
|
|
|
|
Else \var{tz} must be an instance of a class \class{tzinfo} subclass,
|
|
and the current date and time are converted to \var{tz}'s time
|
|
zone. In this case the result is equivalent to
|
|
\code{\var{tz}.fromutc(datetime.utcnow().replace(tzinfo=\var{tz}))}.
|
|
See also \method{today()}, \method{utcnow()}.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{utcnow}{}
|
|
Return the current UTC date and time, with \member{tzinfo} \code{None}.
|
|
This is like \method{now()}, but returns the current UTC date and time,
|
|
as a naive \class{datetime} object.
|
|
See also \method{now()}.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{fromtimestamp}{timestamp, tz=None}
|
|
Return the local date and time corresponding to the \POSIX{}
|
|
timestamp, such as is returned by \function{time.time()}.
|
|
If optional argument \var{tz} is \code{None} or not specified, the
|
|
timestamp is converted to the platform's local date and time, and
|
|
the returned \class{datetime} object is naive.
|
|
|
|
Else \var{tz} must be an instance of a class \class{tzinfo} subclass,
|
|
and the timestamp is converted to \var{tz}'s time zone. In this case
|
|
the result is equivalent to
|
|
\code{\var{tz}.fromutc(datetime.utcfromtimestamp(\var{timestamp}).replace(tzinfo=\var{tz}))}.
|
|
|
|
\method{fromtimestamp()} may raise \exception{ValueError}, if the
|
|
timestamp is out of the range of values supported by the platform C
|
|
\cfunction{localtime()} or \cfunction{gmtime()} functions. It's common
|
|
for this to be restricted to years in 1970 through 2038.
|
|
Note that on non-POSIX systems that include leap seconds in their
|
|
notion of a timestamp, leap seconds are ignored by
|
|
\method{fromtimestamp()}, and then it's possible to have two timestamps
|
|
differing by a second that yield identical \class{datetime} objects.
|
|
See also \method{utcfromtimestamp()}.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{utcfromtimestamp}{timestamp}
|
|
Return the UTC \class{datetime} corresponding to the \POSIX{}
|
|
timestamp, with \member{tzinfo} \code{None}.
|
|
This may raise \exception{ValueError}, if the
|
|
timestamp is out of the range of values supported by the platform
|
|
C \cfunction{gmtime()} function. It's common for this to be
|
|
restricted to years in 1970 through 2038.
|
|
See also \method{fromtimestamp()}.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{fromordinal}{ordinal}
|
|
Return the \class{datetime} corresponding to the proleptic
|
|
Gregorian ordinal, where January 1 of year 1 has ordinal 1.
|
|
\exception{ValueError} is raised unless \code{1 <= ordinal <=
|
|
datetime.max.toordinal()}. The hour, minute, second and
|
|
microsecond of the result are all 0,
|
|
and \member{tzinfo} is \code{None}.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{combine}{date, time}
|
|
Return a new \class{datetime} object whose date members are
|
|
equal to the given \class{date} object's, and whose time
|
|
and \member{tzinfo} members are equal to the given \class{time} object's.
|
|
For any \class{datetime} object \var{d}, \code{\var{d} ==
|
|
datetime.combine(\var{d}.date(), \var{d}.timetz())}. If date is a
|
|
\class{datetime} object, its time and \member{tzinfo} members are
|
|
ignored.
|
|
\end{methoddesc}
|
|
|
|
Class attributes:
|
|
|
|
\begin{memberdesc}{min}
|
|
The earliest representable \class{datetime},
|
|
\code{datetime(MINYEAR, 1, 1, tzinfo=None)}.
|
|
\end{memberdesc}
|
|
|
|
\begin{memberdesc}{max}
|
|
The latest representable \class{datetime},
|
|
\code{datetime(MAXYEAR, 12, 31, 23, 59, 59, 999999, tzinfo=None)}.
|
|
\end{memberdesc}
|
|
|
|
\begin{memberdesc}{resolution}
|
|
The smallest possible difference between non-equal \class{datetime}
|
|
objects, \code{timedelta(microseconds=1)}.
|
|
\end{memberdesc}
|
|
|
|
Instance attributes (read-only):
|
|
|
|
\begin{memberdesc}{year}
|
|
Between \constant{MINYEAR} and \constant{MAXYEAR} inclusive.
|
|
\end{memberdesc}
|
|
|
|
\begin{memberdesc}{month}
|
|
Between 1 and 12 inclusive.
|
|
\end{memberdesc}
|
|
|
|
\begin{memberdesc}{day}
|
|
Between 1 and the number of days in the given month of the given
|
|
year.
|
|
\end{memberdesc}
|
|
|
|
\begin{memberdesc}{hour}
|
|
In \code{range(24)}.
|
|
\end{memberdesc}
|
|
|
|
\begin{memberdesc}{minute}
|
|
In \code{range(60)}.
|
|
\end{memberdesc}
|
|
|
|
\begin{memberdesc}{second}
|
|
In \code{range(60)}.
|
|
\end{memberdesc}
|
|
|
|
\begin{memberdesc}{microsecond}
|
|
In \code{range(1000000)}.
|
|
\end{memberdesc}
|
|
|
|
\begin{memberdesc}{tzinfo}
|
|
The object passed as the \var{tzinfo} argument to the
|
|
\class{datetime} constructor, or \code{None} if none was passed.
|
|
\end{memberdesc}
|
|
|
|
Supported operations:
|
|
|
|
\begin{tableii}{c|l}{code}{Operation}{Result}
|
|
\lineii{\var{datetime2} = \var{datetime1} + \var{timedelta}}{(1)}
|
|
|
|
\lineii{\var{datetime2} = \var{datetime1} - \var{timedelta}}{(2)}
|
|
|
|
\lineii{\var{timedelta} = \var{datetime1} - \var{datetime2}}{(3)}
|
|
|
|
\lineii{\var{datetime1} < \var{datetime2}}
|
|
{Compares \class{datetime} to \class{datetime}.
|
|
(4)}
|
|
|
|
\end{tableii}
|
|
|
|
\begin{description}
|
|
|
|
\item[(1)]
|
|
|
|
datetime2 is a duration of timedelta removed from datetime1, moving
|
|
forward in time if \code{\var{timedelta}.days} > 0, or backward if
|
|
\code{\var{timedelta}.days} < 0. The result has the same \member{tzinfo} member
|
|
as the input datetime, and datetime2 - datetime1 == timedelta after.
|
|
\exception{OverflowError} is raised if datetime2.year would be
|
|
smaller than \constant{MINYEAR} or larger than \constant{MAXYEAR}.
|
|
Note that no time zone adjustments are done even if the input is an
|
|
aware object.
|
|
|
|
\item[(2)]
|
|
Computes the datetime2 such that datetime2 + timedelta == datetime1.
|
|
As for addition, the result has the same \member{tzinfo} member
|
|
as the input datetime, and no time zone adjustments are done even
|
|
if the input is aware.
|
|
This isn't quite equivalent to datetime1 + (-timedelta), because
|
|
-timedelta in isolation can overflow in cases where
|
|
datetime1 - timedelta does not.
|
|
|
|
\item[(3)]
|
|
Subtraction of a \class{datetime} from a
|
|
\class{datetime} is defined only if both
|
|
operands are naive, or if both are aware. If one is aware and the
|
|
other is naive, \exception{TypeError} is raised.
|
|
|
|
If both are naive, or both are aware and have the same \member{tzinfo}
|
|
member, the \member{tzinfo} members are ignored, and the result is
|
|
a \class{timedelta} object \var{t} such that
|
|
\code{\var{datetime2} + \var{t} == \var{datetime1}}. No time zone
|
|
adjustments are done in this case.
|
|
|
|
If both are aware and have different \member{tzinfo} members,
|
|
\code{a-b} acts as if \var{a} and \var{b} were first converted to
|
|
naive UTC datetimes first. The result is
|
|
\code{(\var{a}.replace(tzinfo=None) - \var{a}.utcoffset()) -
|
|
(\var{b}.replace(tzinfo=None) - \var{b}.utcoffset())}
|
|
except that the implementation never overflows.
|
|
|
|
\item[(4)]
|
|
|
|
\var{datetime1} is considered less than \var{datetime2}
|
|
when \var{datetime1} precedes \var{datetime2} in time.
|
|
|
|
If one comparand is naive and
|
|
the other is aware, \exception{TypeError} is raised. If both
|
|
comparands are aware, and have the same \member{tzinfo} member,
|
|
the common \member{tzinfo} member is ignored and the base datetimes
|
|
are compared. If both comparands are aware and have different
|
|
\member{tzinfo} members, the comparands are first adjusted by
|
|
subtracting their UTC offsets (obtained from \code{self.utcoffset()}).
|
|
\note{In order to stop comparison from falling back to the default
|
|
scheme of comparing object addresses, datetime comparison
|
|
normally raises \exception{TypeError} if the other comparand
|
|
isn't also a \class{datetime} object. However,
|
|
\code{NotImplemented} is returned instead if the other comparand
|
|
has a \method{timetuple} attribute. This hook gives other
|
|
kinds of date objects a chance at implementing mixed-type
|
|
comparison. If not, when a \class{datetime} object is
|
|
compared to an object of a different type, \exception{TypeError}
|
|
is raised unless the comparison is \code{==} or \code{!=}. The
|
|
latter cases return \constant{False} or \constant{True},
|
|
respectively.}
|
|
|
|
\end{description}
|
|
|
|
\class{datetime} objects can be used as dictionary keys. In Boolean
|
|
contexts, all \class{datetime} objects are considered to be true.
|
|
|
|
|
|
Instance methods:
|
|
|
|
\begin{methoddesc}{date}{}
|
|
Return \class{date} object with same year, month and day.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{time}{}
|
|
Return \class{time} object with same hour, minute, second and microsecond.
|
|
\member{tzinfo} is \code{None}. See also method \method{timetz()}.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{timetz}{}
|
|
Return \class{time} object with same hour, minute, second, microsecond,
|
|
and tzinfo members. See also method \method{time()}.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{replace}{year=, month=, day=, hour=, minute=, second=,
|
|
microsecond=, tzinfo=}
|
|
Return a datetime with the same members, except for those members given
|
|
new values by whichever keyword arguments are specified. Note that
|
|
\code{tzinfo=None} can be specified to create a naive datetime from
|
|
an aware datetime with no conversion of date and time members.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{astimezone}{tz}
|
|
Return a \class{datetime} object with new \member{tzinfo} member
|
|
\var{tz}, adjusting the date and time members so the result is the
|
|
same UTC time as \var{self}, but in \var{tz}'s local time.
|
|
|
|
\var{tz} must be an instance of a \class{tzinfo} subclass, and its
|
|
\method{utcoffset()} and \method{dst()} methods must not return
|
|
\code{None}. \var{self} must be aware (\code{\var{self}.tzinfo} must
|
|
not be \code{None}, and \code{\var{self}.utcoffset()} must not return
|
|
\code{None}).
|
|
|
|
If \code{\var{self}.tzinfo} is \var{tz},
|
|
\code{\var{self}.astimezone(\var{tz})} is equal to \var{self}: no
|
|
adjustment of date or time members is performed.
|
|
Else the result is local time in time zone \var{tz}, representing the
|
|
same UTC time as \var{self}: after \code{\var{astz} =
|
|
\var{dt}.astimezone(\var{tz})},
|
|
\code{\var{astz} - \var{astz}.utcoffset()} will usually have the same
|
|
date and time members as \code{\var{dt} - \var{dt}.utcoffset()}.
|
|
The discussion of class \class{tzinfo} explains the cases at Daylight
|
|
Saving Time transition boundaries where this cannot be achieved (an issue
|
|
only if \var{tz} models both standard and daylight time).
|
|
|
|
If you merely want to attach a time zone object \var{tz} to a
|
|
datetime \var{dt} without adjustment of date and time members,
|
|
use \code{\var{dt}.replace(tzinfo=\var{tz})}. If
|
|
you merely want to remove the time zone object from an aware datetime
|
|
\var{dt} without conversion of date and time members, use
|
|
\code{\var{dt}.replace(tzinfo=None)}.
|
|
|
|
Note that the default \method{tzinfo.fromutc()} method can be overridden
|
|
in a \class{tzinfo} subclass to affect the result returned by
|
|
\method{astimezone()}. Ignoring error cases, \method{astimezone()}
|
|
acts like:
|
|
|
|
\begin{verbatim}
|
|
def astimezone(self, tz):
|
|
if self.tzinfo is tz:
|
|
return self
|
|
# Convert self to UTC, and attach the new time zone object.
|
|
utc = (self - self.utcoffset()).replace(tzinfo=tz)
|
|
# Convert from UTC to tz's local time.
|
|
return tz.fromutc(utc)
|
|
\end{verbatim}
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{utcoffset}{}
|
|
If \member{tzinfo} is \code{None}, returns \code{None}, else
|
|
returns \code{\var{self}.tzinfo.utcoffset(\var{self})}, and
|
|
raises an exception if the latter doesn't return \code{None}, or
|
|
a \class{timedelta} object representing a whole number of minutes
|
|
with magnitude less than one day.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{dst}{}
|
|
If \member{tzinfo} is \code{None}, returns \code{None}, else
|
|
returns \code{\var{self}.tzinfo.dst(\var{self})}, and
|
|
raises an exception if the latter doesn't return \code{None}, or
|
|
a \class{timedelta} object representing a whole number of minutes
|
|
with magnitude less than one day.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{tzname}{}
|
|
If \member{tzinfo} is \code{None}, returns \code{None}, else
|
|
returns \code{\var{self}.tzinfo.tzname(\var{self})},
|
|
raises an exception if the latter doesn't return \code{None} or
|
|
a string object,
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{timetuple}{}
|
|
Return a \class{time.struct_time} such as returned by
|
|
\function{time.localtime()}.
|
|
\code{\var{d}.timetuple()} is equivalent to
|
|
\code{time.struct_time((\var{d}.year, \var{d}.month, \var{d}.day,
|
|
\var{d}.hour, \var{d}.minute, \var{d}.second,
|
|
\var{d}.weekday(),
|
|
\var{d}.toordinal() - date(\var{d}.year, 1, 1).toordinal() + 1,
|
|
dst))}
|
|
The \member{tm_isdst} flag of the result is set according to
|
|
the \method{dst()} method: \member{tzinfo} is \code{None} or
|
|
\method{dst()} returns \code{None},
|
|
\member{tm_isdst} is set to \code{-1}; else if \method{dst()} returns
|
|
a non-zero value, \member{tm_isdst} is set to \code{1};
|
|
else \code{tm_isdst} is set to \code{0}.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{utctimetuple}{}
|
|
If \class{datetime} instance \var{d} is naive, this is the same as
|
|
\code{\var{d}.timetuple()} except that \member{tm_isdst} is forced to 0
|
|
regardless of what \code{d.dst()} returns. DST is never in effect
|
|
for a UTC time.
|
|
|
|
If \var{d} is aware, \var{d} is normalized to UTC time, by subtracting
|
|
\code{\var{d}.utcoffset()}, and a \class{time.struct_time} for the
|
|
normalized time is returned. \member{tm_isdst} is forced to 0.
|
|
Note that the result's \member{tm_year} member may be
|
|
\constant{MINYEAR}-1 or \constant{MAXYEAR}+1, if \var{d}.year was
|
|
\code{MINYEAR} or \code{MAXYEAR} and UTC adjustment spills over a
|
|
year boundary.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{toordinal}{}
|
|
Return the proleptic Gregorian ordinal of the date. The same as
|
|
\code{self.date().toordinal()}.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{weekday}{}
|
|
Return the day of the week as an integer, where Monday is 0 and
|
|
Sunday is 6. The same as \code{self.date().weekday()}.
|
|
See also \method{isoweekday()}.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{isoweekday}{}
|
|
Return the day of the week as an integer, where Monday is 1 and
|
|
Sunday is 7. The same as \code{self.date().isoweekday()}.
|
|
See also \method{weekday()}, \method{isocalendar()}.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{isocalendar}{}
|
|
Return a 3-tuple, (ISO year, ISO week number, ISO weekday). The
|
|
same as \code{self.date().isocalendar()}.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{isoformat}{sep='T'}
|
|
Return a string representing the date and time in ISO 8601 format,
|
|
YYYY-MM-DDTHH:MM:SS.mmmmmm
|
|
or, if \member{microsecond} is 0,
|
|
YYYY-MM-DDTHH:MM:SS
|
|
|
|
If \method{utcoffset()} does not return \code{None}, a 6-character
|
|
string is appended, giving the UTC offset in (signed) hours and
|
|
minutes:
|
|
YYYY-MM-DDTHH:MM:SS.mmmmmm+HH:MM
|
|
or, if \member{microsecond} is 0
|
|
YYYY-MM-DDTHH:MM:SS+HH:MM
|
|
|
|
The optional argument \var{sep} (default \code{'T'}) is a
|
|
one-character separator, placed between the date and time portions
|
|
of the result. For example,
|
|
|
|
\begin{verbatim}
|
|
>>> from datetime import tzinfo, timedelta, datetime
|
|
>>> class TZ(tzinfo):
|
|
... def utcoffset(self, dt): return timedelta(minutes=-399)
|
|
...
|
|
>>> datetime(2002, 12, 25, tzinfo=TZ()).isoformat(' ')
|
|
'2002-12-25 00:00:00-06:39'
|
|
\end{verbatim}
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{__str__}{}
|
|
For a \class{datetime} instance \var{d}, \code{str(\var{d})} is
|
|
equivalent to \code{\var{d}.isoformat(' ')}.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{ctime}{}
|
|
Return a string representing the date and time, for example
|
|
\code{datetime(2002, 12, 4, 20, 30, 40).ctime() ==
|
|
'Wed Dec 4 20:30:40 2002'}.
|
|
\code{d.ctime()} is equivalent to
|
|
\code{time.ctime(time.mktime(d.timetuple()))} on platforms where
|
|
the native C \cfunction{ctime()} function (which
|
|
\function{time.ctime()} invokes, but which
|
|
\method{datetime.ctime()} does not invoke) conforms to the C
|
|
standard.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{strftime}{format}
|
|
Return a string representing the date and time, controlled by an
|
|
explicit format string. See the section on \method{strftime()}
|
|
behavior.
|
|
\end{methoddesc}
|
|
|
|
|
|
\subsection{\class{time} Objects \label{datetime-time}}
|
|
|
|
A time object represents a (local) time of day, independent of any
|
|
particular day, and subject to adjustment via a \class{tzinfo} object.
|
|
|
|
\begin{classdesc}{time}{hour=0, minute=0, second=0, microsecond=0,
|
|
tzinfo=None}
|
|
All arguments are optional. \var{tzinfo} may be \code{None}, or
|
|
an instance of a \class{tzinfo} subclass. The remaining arguments
|
|
may be ints or longs, in the following ranges:
|
|
|
|
\begin{itemize}
|
|
\item \code{0 <= \var{hour} < 24}
|
|
\item \code{0 <= \var{minute} < 60}
|
|
\item \code{0 <= \var{second} < 60}
|
|
\item \code{0 <= \var{microsecond} < 1000000}.
|
|
\end{itemize}
|
|
|
|
If an argument outside those ranges is given,
|
|
\exception{ValueError} is raised.
|
|
\end{classdesc}
|
|
|
|
Class attributes:
|
|
|
|
\begin{memberdesc}{min}
|
|
The earliest representable \class{time}, \code{time(0, 0, 0, 0)}.
|
|
\end{memberdesc}
|
|
|
|
\begin{memberdesc}{max}
|
|
The latest representable \class{time}, \code{time(23, 59, 59, 999999)}.
|
|
\end{memberdesc}
|
|
|
|
\begin{memberdesc}{resolution}
|
|
The smallest possible difference between non-equal \class{time}
|
|
objects, \code{timedelta(microseconds=1)}, although note that
|
|
arithmetic on \class{time} objects is not supported.
|
|
\end{memberdesc}
|
|
|
|
Instance attributes (read-only):
|
|
|
|
\begin{memberdesc}{hour}
|
|
In \code{range(24)}.
|
|
\end{memberdesc}
|
|
|
|
\begin{memberdesc}{minute}
|
|
In \code{range(60)}.
|
|
\end{memberdesc}
|
|
|
|
\begin{memberdesc}{second}
|
|
In \code{range(60)}.
|
|
\end{memberdesc}
|
|
|
|
\begin{memberdesc}{microsecond}
|
|
In \code{range(1000000)}.
|
|
\end{memberdesc}
|
|
|
|
\begin{memberdesc}{tzinfo}
|
|
The object passed as the tzinfo argument to the \class{time}
|
|
constructor, or \code{None} if none was passed.
|
|
\end{memberdesc}
|
|
|
|
Supported operations:
|
|
|
|
\begin{itemize}
|
|
\item
|
|
comparison of \class{time} to \class{time},
|
|
where \var{a} is considered less than \var{b} when \var{a} precedes
|
|
\var{b} in time. If one comparand is naive and the other is aware,
|
|
\exception{TypeError} is raised. If both comparands are aware, and
|
|
have the same \member{tzinfo} member, the common \member{tzinfo}
|
|
member is ignored and the base times are compared. If both
|
|
comparands are aware and have different \member{tzinfo} members,
|
|
the comparands are first adjusted by subtracting their UTC offsets
|
|
(obtained from \code{self.utcoffset()}).
|
|
In order to stop mixed-type comparisons from falling back to the
|
|
default comparison by object address, when a \class{time} object is
|
|
compared to an object of a different type, \exception{TypeError} is
|
|
raised unless the comparison is \code{==} or \code{!=}. The latter
|
|
cases return \constant{False} or \constant{True}, respectively.
|
|
|
|
\item
|
|
hash, use as dict key
|
|
|
|
\item
|
|
efficient pickling
|
|
|
|
\item
|
|
in Boolean contexts, a \class{time} object is considered to be
|
|
true if and only if, after converting it to minutes and
|
|
subtracting \method{utcoffset()} (or \code{0} if that's
|
|
\code{None}), the result is non-zero.
|
|
\end{itemize}
|
|
|
|
Instance methods:
|
|
|
|
\begin{methoddesc}{replace}(hour=, minute=, second=, microsecond=, tzinfo=)
|
|
Return a \class{time} with the same value, except for those members given
|
|
new values by whichever keyword arguments are specified. Note that
|
|
\code{tzinfo=None} can be specified to create a naive \class{time} from
|
|
an aware \class{time}, without conversion of the time members.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{isoformat}{}
|
|
Return a string representing the time in ISO 8601 format,
|
|
HH:MM:SS.mmmmmm
|
|
or, if self.microsecond is 0,
|
|
HH:MM:SS
|
|
If \method{utcoffset()} does not return \code{None}, a 6-character
|
|
string is appended, giving the UTC offset in (signed) hours and
|
|
minutes:
|
|
HH:MM:SS.mmmmmm+HH:MM
|
|
or, if self.microsecond is 0,
|
|
HH:MM:SS+HH:MM
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{__str__}{}
|
|
For a time \var{t}, \code{str(\var{t})} is equivalent to
|
|
\code{\var{t}.isoformat()}.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{strftime}{format}
|
|
Return a string representing the time, controlled by an explicit
|
|
format string. See the section on \method{strftime()} behavior.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{utcoffset}{}
|
|
If \member{tzinfo} is \code{None}, returns \code{None}, else
|
|
returns \code{\var{self}.tzinfo.utcoffset(None)}, and
|
|
raises an exception if the latter doesn't return \code{None} or
|
|
a \class{timedelta} object representing a whole number of minutes
|
|
with magnitude less than one day.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{dst}{}
|
|
If \member{tzinfo} is \code{None}, returns \code{None}, else
|
|
returns \code{\var{self}.tzinfo.dst(None)}, and
|
|
raises an exception if the latter doesn't return \code{None}, or
|
|
a \class{timedelta} object representing a whole number of minutes
|
|
with magnitude less than one day.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{tzname}{}
|
|
If \member{tzinfo} is \code{None}, returns \code{None}, else
|
|
returns \code{\var{self}.tzinfo.tzname(None)}, or
|
|
raises an exception if the latter doesn't return \code{None} or
|
|
a string object.
|
|
\end{methoddesc}
|
|
|
|
|
|
\subsection{\class{tzinfo} Objects \label{datetime-tzinfo}}
|
|
|
|
\class{tzinfo} is an abstract base clase, meaning that this class
|
|
should not be instantiated directly. You need to derive a concrete
|
|
subclass, and (at least) supply implementations of the standard
|
|
\class{tzinfo} methods needed by the \class{datetime} methods you
|
|
use. The \module{datetime} module does not supply any concrete
|
|
subclasses of \class{tzinfo}.
|
|
|
|
An instance of (a concrete subclass of) \class{tzinfo} can be passed
|
|
to the constructors for \class{datetime} and \class{time} objects.
|
|
The latter objects view their members as being in local time, and the
|
|
\class{tzinfo} object supports methods revealing offset of local time
|
|
from UTC, the name of the time zone, and DST offset, all relative to a
|
|
date or time object passed to them.
|
|
|
|
Special requirement for pickling: A \class{tzinfo} subclass must have an
|
|
\method{__init__} method that can be called with no arguments, else it
|
|
can be pickled but possibly not unpickled again. This is a technical
|
|
requirement that may be relaxed in the future.
|
|
|
|
A concrete subclass of \class{tzinfo} may need to implement the
|
|
following methods. Exactly which methods are needed depends on the
|
|
uses made of aware \module{datetime} objects. If in doubt, simply
|
|
implement all of them.
|
|
|
|
\begin{methoddesc}{utcoffset}{self, dt}
|
|
Return offset of local time from UTC, in minutes east of UTC. If
|
|
local time is west of UTC, this should be negative. Note that this
|
|
is intended to be the total offset from UTC; for example, if a
|
|
\class{tzinfo} object represents both time zone and DST adjustments,
|
|
\method{utcoffset()} should return their sum. If the UTC offset
|
|
isn't known, return \code{None}. Else the value returned must be
|
|
a \class{timedelta} object specifying a whole number of minutes in the
|
|
range -1439 to 1439 inclusive (1440 = 24*60; the magnitude of the offset
|
|
must be less than one day). Most implementations of
|
|
\method{utcoffset()} will probably look like one of these two:
|
|
|
|
\begin{verbatim}
|
|
return CONSTANT # fixed-offset class
|
|
return CONSTANT + self.dst(dt) # daylight-aware class
|
|
\end{verbatim}
|
|
|
|
If \method{utcoffset()} does not return \code{None},
|
|
\method{dst()} should not return \code{None} either.
|
|
|
|
The default implementation of \method{utcoffset()} raises
|
|
\exception{NotImplementedError}.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{dst}{self, dt}
|
|
Return the daylight saving time (DST) adjustment, in minutes east of
|
|
UTC, or \code{None} if DST information isn't known. Return
|
|
\code{timedelta(0)} if DST is not in effect.
|
|
If DST is in effect, return the offset as a
|
|
\class{timedelta} object (see \method{utcoffset()} for details).
|
|
Note that DST offset, if applicable, has
|
|
already been added to the UTC offset returned by
|
|
\method{utcoffset()}, so there's no need to consult \method{dst()}
|
|
unless you're interested in obtaining DST info separately. For
|
|
example, \method{datetime.timetuple()} calls its \member{tzinfo}
|
|
member's \method{dst()} method to determine how the
|
|
\member{tm_isdst} flag should be set, and
|
|
\method{tzinfo.fromutc()} calls \method{dst()} to account for
|
|
DST changes when crossing time zones.
|
|
|
|
An instance \var{tz} of a \class{tzinfo} subclass that models both
|
|
standard and daylight times must be consistent in this sense:
|
|
|
|
\code{\var{tz}.utcoffset(\var{dt}) - \var{tz}.dst(\var{dt})}
|
|
|
|
must return the same result for every \class{datetime} \var{dt}
|
|
with \code{\var{dt}.tzinfo==\var{tz}} For sane \class{tzinfo}
|
|
subclasses, this expression yields the time zone's "standard offset",
|
|
which should not depend on the date or the time, but only on geographic
|
|
location. The implementation of \method{datetime.astimezone()} relies
|
|
on this, but cannot detect violations; it's the programmer's
|
|
responsibility to ensure it. If a \class{tzinfo} subclass cannot
|
|
guarantee this, it may be able to override the default implementation
|
|
of \method{tzinfo.fromutc()} to work correctly with \method{astimezone()}
|
|
regardless.
|
|
|
|
Most implementations of \method{dst()} will probably look like one
|
|
of these two:
|
|
|
|
\begin{verbatim}
|
|
return timedelta(0) # a fixed-offset class: doesn't account for DST
|
|
|
|
or
|
|
|
|
# Code to set dston and dstoff to the time zone's DST transition
|
|
# times based on the input dt.year, and expressed in standard local
|
|
# time. Then
|
|
|
|
if dston <= dt.replace(tzinfo=None) < dstoff:
|
|
return timedelta(hours=1)
|
|
else:
|
|
return timedelta(0)
|
|
\end{verbatim}
|
|
|
|
The default implementation of \method{dst()} raises
|
|
\exception{NotImplementedError}.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{tzname}{self, dt}
|
|
Return the time zone name corresponding to the \class{datetime}
|
|
object \var{dt}, as a string.
|
|
Nothing about string names is defined by the
|
|
\module{datetime} module, and there's no requirement that it mean
|
|
anything in particular. For example, "GMT", "UTC", "-500", "-5:00",
|
|
"EDT", "US/Eastern", "America/New York" are all valid replies. Return
|
|
\code{None} if a string name isn't known. Note that this is a method
|
|
rather than a fixed string primarily because some \class{tzinfo}
|
|
subclasses will wish to return different names depending on the specific
|
|
value of \var{dt} passed, especially if the \class{tzinfo} class is
|
|
accounting for daylight time.
|
|
|
|
The default implementation of \method{tzname()} raises
|
|
\exception{NotImplementedError}.
|
|
\end{methoddesc}
|
|
|
|
These methods are called by a \class{datetime} or \class{time} object,
|
|
in response to their methods of the same names. A \class{datetime}
|
|
object passes itself as the argument, and a \class{time} object passes
|
|
\code{None} as the argument. A \class{tzinfo} subclass's methods should
|
|
therefore be prepared to accept a \var{dt} argument of \code{None}, or of
|
|
class \class{datetime}.
|
|
|
|
When \code{None} is passed, it's up to the class designer to decide the
|
|
best response. For example, returning \code{None} is appropriate if the
|
|
class wishes to say that time objects don't participate in the
|
|
\class{tzinfo} protocols. It may be more useful for \code{utcoffset(None)}
|
|
to return the standard UTC offset, as there is no other convention for
|
|
discovering the standard offset.
|
|
|
|
When a \class{datetime} object is passed in response to a
|
|
\class{datetime} method, \code{dt.tzinfo} is the same object as
|
|
\var{self}. \class{tzinfo} methods can rely on this, unless
|
|
user code calls \class{tzinfo} methods directly. The intent is that
|
|
the \class{tzinfo} methods interpret \var{dt} as being in local time,
|
|
and not need worry about objects in other timezones.
|
|
|
|
There is one more \class{tzinfo} method that a subclass may wish to
|
|
override:
|
|
|
|
\begin{methoddesc}{fromutc}{self, dt}
|
|
This is called from the default \class{datetime.astimezone()}
|
|
implementation. When called from that, \code{\var{dt}.tzinfo} is
|
|
\var{self}, and \var{dt}'s date and time members are to be viewed as
|
|
expressing a UTC time. The purpose of \method{fromutc()} is to
|
|
adjust the date and time members, returning an equivalent datetime in
|
|
\var{self}'s local time.
|
|
|
|
Most \class{tzinfo} subclasses should be able to inherit the default
|
|
\method{fromutc()} implementation without problems. It's strong enough
|
|
to handle fixed-offset time zones, and time zones accounting for both
|
|
standard and daylight time, and the latter even if the DST transition
|
|
times differ in different years. An example of a time zone the default
|
|
\method{fromutc()} implementation may not handle correctly in all cases
|
|
is one where the standard offset (from UTC) depends on the specific date
|
|
and time passed, which can happen for political reasons.
|
|
The default implementations of \method{astimezone()} and
|
|
\method{fromutc()} may not produce the result you want if the result is
|
|
one of the hours straddling the moment the standard offset changes.
|
|
|
|
Skipping code for error cases, the default \method{fromutc()}
|
|
implementation acts like:
|
|
|
|
\begin{verbatim}
|
|
def fromutc(self, dt):
|
|
# raise ValueError error if dt.tzinfo is not self
|
|
dtoff = dt.utcoffset()
|
|
dtdst = dt.dst()
|
|
# raise ValueError if dtoff is None or dtdst is None
|
|
delta = dtoff - dtdst # this is self's standard offset
|
|
if delta:
|
|
dt += delta # convert to standard local time
|
|
dtdst = dt.dst()
|
|
# raise ValueError if dtdst is None
|
|
if dtdst:
|
|
return dt + dtdst
|
|
else:
|
|
return dt
|
|
\end{verbatim}
|
|
\end{methoddesc}
|
|
|
|
Example \class{tzinfo} classes:
|
|
|
|
\verbatiminput{tzinfo-examples.py}
|
|
|
|
Note that there are unavoidable subtleties twice per year in a
|
|
\class{tzinfo}
|
|
subclass accounting for both standard and daylight time, at the DST
|
|
transition points. For concreteness, consider US Eastern (UTC -0500),
|
|
where EDT begins the minute after 1:59 (EST) on the first Sunday in
|
|
April, and ends the minute after 1:59 (EDT) on the last Sunday in October:
|
|
|
|
\begin{verbatim}
|
|
UTC 3:MM 4:MM 5:MM 6:MM 7:MM 8:MM
|
|
EST 22:MM 23:MM 0:MM 1:MM 2:MM 3:MM
|
|
EDT 23:MM 0:MM 1:MM 2:MM 3:MM 4:MM
|
|
|
|
start 22:MM 23:MM 0:MM 1:MM 3:MM 4:MM
|
|
|
|
end 23:MM 0:MM 1:MM 1:MM 2:MM 3:MM
|
|
\end{verbatim}
|
|
|
|
When DST starts (the "start" line), the local wall clock leaps from 1:59
|
|
to 3:00. A wall time of the form 2:MM doesn't really make sense on that
|
|
day, so \code{astimezone(Eastern)} won't deliver a result with
|
|
\code{hour==2} on the
|
|
day DST begins. In order for \method{astimezone()} to make this
|
|
guarantee, the \method{rzinfo.dst()} method must consider times
|
|
in the "missing hour" (2:MM for Eastern) to be in daylight time.
|
|
|
|
When DST ends (the "end" line), there's a potentially worse problem:
|
|
there's an hour that can't be spelled unambiguously in local wall time:
|
|
the last hour of daylight time. In Eastern, that's times of
|
|
the form 5:MM UTC on the day daylight time ends. The local wall clock
|
|
leaps from 1:59 (daylight time) back to 1:00 (standard time) again.
|
|
Local times of the form 1:MM are ambiguous. \method{astimezone()} mimics
|
|
the local clock's behavior by mapping two adjacent UTC hours into the
|
|
same local hour then. In the Eastern example, UTC times of the form
|
|
5:MM and 6:MM both map to 1:MM when converted to Eastern. In order for
|
|
\method{astimezone()} to make this guarantee, the \method{tzinfo.dst()}
|
|
method must consider times in the "repeated hour" to be in
|
|
standard time. This is easily arranged, as in the example, by expressing
|
|
DST switch times in the time zone's standard local time.
|
|
|
|
Applications that can't bear such ambiguities should avoid using hybrid
|
|
\class{tzinfo} subclasses; there are no ambiguities when using UTC, or
|
|
any other fixed-offset \class{tzinfo} subclass (such as a class
|
|
representing only EST (fixed offset -5 hours), or only EDT (fixed offset
|
|
-4 hours)).
|
|
|
|
|
|
\subsection{\method{strftime()} Behavior}
|
|
|
|
\class{date}, \class{datetime}, and \class{time}
|
|
objects all support a \code{strftime(\var{format})}
|
|
method, to create a string representing the time under the control of
|
|
an explicit format string. Broadly speaking,
|
|
\code{d.strftime(fmt)}
|
|
acts like the \refmodule{time} module's
|
|
\code{time.strftime(fmt, d.timetuple())}
|
|
although not all objects support a \method{timetuple()} method.
|
|
|
|
For \class{time} objects, the format codes for
|
|
year, month, and day should not be used, as time objects have no such
|
|
values. If they're used anyway, \code{1900} is substituted for the
|
|
year, and \code{0} for the month and day.
|
|
|
|
For \class{date} objects, the format codes for hours, minutes, and
|
|
seconds should not be used, as \class{date} objects have no such
|
|
values. If they're used anyway, \code{0} is substituted for them.
|
|
|
|
For a naive object, the \code{\%z} and \code{\%Z} format codes are
|
|
replaced by empty strings.
|
|
|
|
For an aware object:
|
|
|
|
\begin{itemize}
|
|
\item[\code{\%z}]
|
|
\method{utcoffset()} is transformed into a 5-character string of
|
|
the form +HHMM or -HHMM, where HH is a 2-digit string giving the
|
|
number of UTC offset hours, and MM is a 2-digit string giving the
|
|
number of UTC offset minutes. For example, if
|
|
\method{utcoffset()} returns \code{timedelta(hours=-3, minutes=-30)},
|
|
\code{\%z} is replaced with the string \code{'-0330'}.
|
|
|
|
\item[\code{\%Z}]
|
|
If \method{tzname()} returns \code{None}, \code{\%Z} is replaced
|
|
by an empty string. Otherwise \code{\%Z} is replaced by the returned
|
|
value, which must be a string.
|
|
\end{itemize}
|
|
|
|
The full set of format codes supported varies across platforms,
|
|
because Python calls the platform C library's \function{strftime()}
|
|
function, and platform variations are common. The documentation for
|
|
Python's \refmodule{time} module lists the format codes that the C
|
|
standard (1989 version) requires, and those work on all platforms
|
|
with a standard C implementation. Note that the 1999 version of the
|
|
C standard added additional format codes.
|
|
|
|
The exact range of years for which \method{strftime()} works also
|
|
varies across platforms. Regardless of platform, years before 1900
|
|
cannot be used.
|
|
|