| .. % XXX what order should the types be discussed in? |
| |
| |
| :mod:`datetime` --- Basic date and time types |
| ============================================= |
| |
| .. module:: datetime |
| :synopsis: Basic date and time types. |
| .. moduleauthor:: Tim Peters <tim@zope.com> |
| .. sectionauthor:: Tim Peters <tim@zope.com> |
| .. sectionauthor:: A.M. Kuchling <amk@amk.ca> |
| |
| |
| The :mod:`datetime` module supplies classes for manipulating dates and times in |
| both simple and complex ways. While date and time arithmetic is supported, the |
| focus of the implementation is on efficient member extraction for output |
| formatting and manipulation. For related |
| functionality, see also the :mod:`time` and :mod:`calendar` modules. |
| |
| There are two kinds of date and time objects: "naive" and "aware". This |
| distinction refers to whether the object has any notion of time zone, daylight |
| saving time, or other kind of algorithmic or political time adjustment. Whether |
| a naive :class:`datetime` object represents Coordinated Universal Time (UTC), |
| local time, or time in some other timezone is purely up to the program, just |
| like it's up to the program whether a particular number represents metres, |
| miles, or mass. Naive :class:`datetime` objects are easy to understand and to |
| work with, at the cost of ignoring some aspects of reality. |
| |
| For applications requiring more, :class:`datetime` and :class:`time` objects |
| have an optional time zone information member, :attr:`tzinfo`, that can contain |
| an instance of a subclass of the abstract :class:`tzinfo` class. These |
| :class:`tzinfo` objects capture information about the offset from UTC time, the |
| time zone name, and whether Daylight Saving Time is in effect. Note that no |
| concrete :class:`tzinfo` classes are supplied by the :mod:`datetime` module. |
| Supporting timezones at whatever level of detail is required is up to the |
| application. The rules for time adjustment across the world are more political |
| than rational, and there is no standard suitable for every application. |
| |
| The :mod:`datetime` module exports the following constants: |
| |
| |
| .. data:: MINYEAR |
| |
| The smallest year number allowed in a :class:`date` or :class:`datetime` object. |
| :const:`MINYEAR` is ``1``. |
| |
| |
| .. data:: MAXYEAR |
| |
| The largest year number allowed in a :class:`date` or :class:`datetime` object. |
| :const:`MAXYEAR` is ``9999``. |
| |
| |
| .. seealso:: |
| |
| Module :mod:`calendar` |
| General calendar related functions. |
| |
| Module :mod:`time` |
| Time access and conversions. |
| |
| |
| Available Types |
| --------------- |
| |
| |
| .. class:: date |
| |
| An idealized naive date, assuming the current Gregorian calendar always was, and |
| always will be, in effect. Attributes: :attr:`year`, :attr:`month`, and |
| :attr:`day`. |
| |
| |
| .. class:: time |
| |
| An idealized time, independent of any particular day, assuming that every day |
| has exactly 24\*60\*60 seconds (there is no notion of "leap seconds" here). |
| Attributes: :attr:`hour`, :attr:`minute`, :attr:`second`, :attr:`microsecond`, |
| and :attr:`tzinfo`. |
| |
| |
| .. class:: datetime |
| |
| A combination of a date and a time. Attributes: :attr:`year`, :attr:`month`, |
| :attr:`day`, :attr:`hour`, :attr:`minute`, :attr:`second`, :attr:`microsecond`, |
| and :attr:`tzinfo`. |
| |
| |
| .. class:: timedelta |
| |
| A duration expressing the difference between two :class:`date`, :class:`time`, |
| or :class:`datetime` instances to microsecond resolution. |
| |
| |
| .. class:: tzinfo |
| |
| An abstract base class for time zone information objects. These are used by the |
| :class:`datetime` and :class:`time` classes to provide a customizable notion of |
| time adjustment (for example, to account for time zone and/or daylight saving |
| time). |
| |
| Objects of these types are immutable. |
| |
| Objects of the :class:`date` type are always naive. |
| |
| An object *d* of type :class:`time` or :class:`datetime` may be naive or aware. |
| *d* is aware if ``d.tzinfo`` is not ``None`` and ``d.tzinfo.utcoffset(d)`` does |
| not return ``None``. If ``d.tzinfo`` is ``None``, or if ``d.tzinfo`` is not |
| ``None`` but ``d.tzinfo.utcoffset(d)`` returns ``None``, *d* is naive. |
| |
| The distinction between naive and aware doesn't apply to :class:`timedelta` |
| objects. |
| |
| Subclass relationships:: |
| |
| object |
| timedelta |
| tzinfo |
| time |
| date |
| datetime |
| |
| |
| .. _datetime-timedelta: |
| |
| :class:`timedelta` Objects |
| -------------------------- |
| |
| A :class:`timedelta` object represents a duration, the difference between two |
| dates or times. |
| |
| |
| .. class:: timedelta([days[, seconds[, microseconds[, milliseconds[, minutes[, hours[, weeks]]]]]]]) |
| |
| All arguments are optional and default to ``0``. Arguments may be ints, longs, |
| or floats, and may be positive or negative. |
| |
| Only *days*, *seconds* and *microseconds* are stored internally. Arguments are |
| converted to those units: |
| |
| * A millisecond is converted to 1000 microseconds. |
| * A minute is converted to 60 seconds. |
| * An hour is converted to 3600 seconds. |
| * A week is converted to 7 days. |
| |
| and days, seconds and microseconds are then normalized so that the |
| representation is unique, with |
| |
| * ``0 <= microseconds < 1000000`` |
| * ``0 <= seconds < 3600*24`` (the number of seconds in one day) |
| * ``-999999999 <= days <= 999999999`` |
| |
| If any argument is a float and there are fractional microseconds, the fractional |
| microseconds left over from all arguments are combined and their sum is rounded |
| to the nearest microsecond. If no argument is a float, the conversion and |
| normalization processes are exact (no information is lost). |
| |
| If the normalized value of days lies outside the indicated range, |
| :exc:`OverflowError` is raised. |
| |
| Note that normalization of negative values may be surprising at first. For |
| example, :: |
| |
| >>> d = timedelta(microseconds=-1) |
| >>> (d.days, d.seconds, d.microseconds) |
| (-1, 86399, 999999) |
| |
| Class attributes are: |
| |
| |
| .. attribute:: timedelta.min |
| |
| The most negative :class:`timedelta` object, ``timedelta(-999999999)``. |
| |
| |
| .. attribute:: timedelta.max |
| |
| The most positive :class:`timedelta` object, ``timedelta(days=999999999, |
| hours=23, minutes=59, seconds=59, microseconds=999999)``. |
| |
| |
| .. attribute:: timedelta.resolution |
| |
| The smallest possible difference between non-equal :class:`timedelta` objects, |
| ``timedelta(microseconds=1)``. |
| |
| Note that, because of normalization, ``timedelta.max`` > ``-timedelta.min``. |
| ``-timedelta.max`` is not representable as a :class:`timedelta` object. |
| |
| Instance attributes (read-only): |
| |
| +------------------+--------------------------------------------+ |
| | Attribute | Value | |
| +==================+============================================+ |
| | ``days`` | Between -999999999 and 999999999 inclusive | |
| +------------------+--------------------------------------------+ |
| | ``seconds`` | Between 0 and 86399 inclusive | |
| +------------------+--------------------------------------------+ |
| | ``microseconds`` | Between 0 and 999999 inclusive | |
| +------------------+--------------------------------------------+ |
| |
| Supported operations: |
| |
| .. % XXX this table is too wide! |
| |
| +--------------------------------+-----------------------------------------------+ |
| | Operation | Result | |
| +================================+===============================================+ |
| | ``t1 = t2 + t3`` | Sum of *t2* and *t3*. Afterwards *t1*-*t2* == | |
| | | *t3* and *t1*-*t3* == *t2* are true. (1) | |
| +--------------------------------+-----------------------------------------------+ |
| | ``t1 = t2 - t3`` | Difference of *t2* and *t3*. Afterwards *t1* | |
| | | == *t2* - *t3* and *t2* == *t1* + *t3* are | |
| | | true. (1) | |
| +--------------------------------+-----------------------------------------------+ |
| | ``t1 = t2 * i or t1 = i * t2`` | Delta multiplied by an integer or long. | |
| | | Afterwards *t1* // i == *t2* is true, | |
| | | provided ``i != 0``. | |
| +--------------------------------+-----------------------------------------------+ |
| | | In general, *t1* \* i == *t1* \* (i-1) + *t1* | |
| | | is true. (1) | |
| +--------------------------------+-----------------------------------------------+ |
| | ``t1 = t2 // i`` | The floor is computed and the remainder (if | |
| | | any) is thrown away. (3) | |
| +--------------------------------+-----------------------------------------------+ |
| | ``+t1`` | Returns a :class:`timedelta` object with the | |
| | | same value. (2) | |
| +--------------------------------+-----------------------------------------------+ |
| | ``-t1`` | equivalent to :class:`timedelta`\ | |
| | | (-*t1.days*, -*t1.seconds*, | |
| | | -*t1.microseconds*), and to *t1*\* -1. (1)(4) | |
| +--------------------------------+-----------------------------------------------+ |
| | ``abs(t)`` | equivalent to +*t* when ``t.days >= 0``, and | |
| | | to -*t* when ``t.days < 0``. (2) | |
| +--------------------------------+-----------------------------------------------+ |
| |
| Notes: |
| |
| (1) |
| This is exact, but may overflow. |
| |
| (2) |
| This is exact, and cannot overflow. |
| |
| (3) |
| Division by 0 raises :exc:`ZeroDivisionError`. |
| |
| (4) |
| -*timedelta.max* is not representable as a :class:`timedelta` object. |
| |
| In addition to the operations listed above :class:`timedelta` objects support |
| certain additions and subtractions with :class:`date` and :class:`datetime` |
| objects (see below). |
| |
| Comparisons of :class:`timedelta` objects are supported with the |
| :class:`timedelta` object representing the smaller duration considered to be the |
| smaller timedelta. In order to stop mixed-type comparisons from falling back to |
| the default comparison by object address, when a :class:`timedelta` object is |
| compared to an object of a different type, :exc:`TypeError` is raised unless the |
| comparison is ``==`` or ``!=``. The latter cases return :const:`False` or |
| :const:`True`, respectively. |
| |
| :class:`timedelta` objects are :term:`hashable` (usable as dictionary keys), support |
| efficient pickling, and in Boolean contexts, a :class:`timedelta` object is |
| considered to be true if and only if it isn't equal to ``timedelta(0)``. |
| |
| |
| .. _datetime-date: |
| |
| :class:`date` Objects |
| --------------------- |
| |
| A :class:`date` object represents a date (year, month and day) in an idealized |
| calendar, the current Gregorian calendar indefinitely extended in both |
| directions. January 1 of year 1 is called day number 1, January 2 of year 1 is |
| called day number 2, and so on. This matches the definition of the "proleptic |
| Gregorian" calendar in Dershowitz and Reingold's book Calendrical Calculations, |
| where it's the base calendar for all computations. See the book for algorithms |
| for converting between proleptic Gregorian ordinals and many other calendar |
| systems. |
| |
| |
| .. class:: date(year, month, day) |
| |
| All arguments are required. Arguments may be ints or longs, in the following |
| ranges: |
| |
| * ``MINYEAR <= year <= MAXYEAR`` |
| * ``1 <= month <= 12`` |
| * ``1 <= day <= number of days in the given month and year`` |
| |
| If an argument outside those ranges is given, :exc:`ValueError` is raised. |
| |
| Other constructors, all class methods: |
| |
| |
| .. method:: date.today() |
| |
| Return the current local date. This is equivalent to |
| ``date.fromtimestamp(time.time())``. |
| |
| |
| .. method:: date.fromtimestamp(timestamp) |
| |
| Return the local date corresponding to the POSIX timestamp, such as is returned |
| by :func:`time.time`. This may raise :exc:`ValueError`, if the timestamp is out |
| of the range of values supported by the platform C :cfunc:`localtime` function. |
| It's common for this to be restricted to years from 1970 through 2038. Note |
| that on non-POSIX systems that include leap seconds in their notion of a |
| timestamp, leap seconds are ignored by :meth:`fromtimestamp`. |
| |
| |
| .. method:: date.fromordinal(ordinal) |
| |
| Return the date corresponding to the proleptic Gregorian ordinal, where January |
| 1 of year 1 has ordinal 1. :exc:`ValueError` is raised unless ``1 <= ordinal <= |
| date.max.toordinal()``. For any date *d*, ``date.fromordinal(d.toordinal()) == |
| d``. |
| |
| Class attributes: |
| |
| |
| .. attribute:: date.min |
| |
| The earliest representable date, ``date(MINYEAR, 1, 1)``. |
| |
| |
| .. attribute:: date.max |
| |
| The latest representable date, ``date(MAXYEAR, 12, 31)``. |
| |
| |
| .. attribute:: date.resolution |
| |
| The smallest possible difference between non-equal date objects, |
| ``timedelta(days=1)``. |
| |
| Instance attributes (read-only): |
| |
| |
| .. attribute:: date.year |
| |
| Between :const:`MINYEAR` and :const:`MAXYEAR` inclusive. |
| |
| |
| .. attribute:: date.month |
| |
| Between 1 and 12 inclusive. |
| |
| |
| .. attribute:: date.day |
| |
| Between 1 and the number of days in the given month of the given year. |
| |
| Supported operations: |
| |
| +-------------------------------+----------------------------------------------+ |
| | Operation | Result | |
| +===============================+==============================================+ |
| | ``date2 = date1 + timedelta`` | *date2* is ``timedelta.days`` days removed | |
| | | from *date1*. (1) | |
| +-------------------------------+----------------------------------------------+ |
| | ``date2 = date1 - timedelta`` | Computes *date2* such that ``date2 + | |
| | | timedelta == date1``. (2) | |
| +-------------------------------+----------------------------------------------+ |
| | ``timedelta = date1 - date2`` | \(3) | |
| +-------------------------------+----------------------------------------------+ |
| | ``date1 < date2`` | *date1* is considered less than *date2* when | |
| | | *date1* precedes *date2* in time. (4) | |
| +-------------------------------+----------------------------------------------+ |
| |
| Notes: |
| |
| (1) |
| *date2* is moved forward in time if ``timedelta.days > 0``, or backward if |
| ``timedelta.days < 0``. Afterward ``date2 - date1 == timedelta.days``. |
| ``timedelta.seconds`` and ``timedelta.microseconds`` are ignored. |
| :exc:`OverflowError` is raised if ``date2.year`` would be smaller than |
| :const:`MINYEAR` or larger than :const:`MAXYEAR`. |
| |
| (2) |
| This isn't quite equivalent to date1 + (-timedelta), because -timedelta in |
| isolation can overflow in cases where date1 - timedelta does not. |
| ``timedelta.seconds`` and ``timedelta.microseconds`` are ignored. |
| |
| (3) |
| This is exact, and cannot overflow. timedelta.seconds and |
| timedelta.microseconds are 0, and date2 + timedelta == date1 after. |
| |
| (4) |
| In other words, ``date1 < date2`` if and only if ``date1.toordinal() < |
| date2.toordinal()``. In order to stop comparison from falling back to the |
| default scheme of comparing object addresses, date comparison normally raises |
| :exc:`TypeError` if the other comparand isn't also a :class:`date` object. |
| However, ``NotImplemented`` is returned instead if the other comparand has a |
| :meth:`timetuple` attribute. This hook gives other kinds of date objects a |
| chance at implementing mixed-type comparison. If not, when a :class:`date` |
| object is compared to an object of a different type, :exc:`TypeError` is raised |
| unless the comparison is ``==`` or ``!=``. The latter cases return |
| :const:`False` or :const:`True`, respectively. |
| |
| Dates can be used as dictionary keys. In Boolean contexts, all :class:`date` |
| objects are considered to be true. |
| |
| Instance methods: |
| |
| |
| .. method:: date.replace(year, month, day) |
| |
| Return a date with the same value, except for those members given new values by |
| whichever keyword arguments are specified. For example, if ``d == date(2002, |
| 12, 31)``, then ``d.replace(day=26) == date(2002, 12, 26)``. |
| |
| |
| .. method:: date.timetuple() |
| |
| Return a :class:`time.struct_time` such as returned by :func:`time.localtime`. |
| The hours, minutes and seconds are 0, and the DST flag is -1. ``d.timetuple()`` |
| is equivalent to ``time.struct_time((d.year, d.month, d.day, 0, 0, 0, |
| d.weekday(), d.toordinal() - date(d.year, 1, 1).toordinal() + 1, -1))`` |
| |
| |
| .. method:: date.toordinal() |
| |
| Return the proleptic Gregorian ordinal of the date, where January 1 of year 1 |
| has ordinal 1. For any :class:`date` object *d*, |
| ``date.fromordinal(d.toordinal()) == d``. |
| |
| |
| .. method:: date.weekday() |
| |
| Return the day of the week as an integer, where Monday is 0 and Sunday is 6. |
| For example, ``date(2002, 12, 4).weekday() == 2``, a Wednesday. See also |
| :meth:`isoweekday`. |
| |
| |
| .. method:: date.isoweekday() |
| |
| Return the day of the week as an integer, where Monday is 1 and Sunday is 7. |
| For example, ``date(2002, 12, 4).isoweekday() == 3``, a Wednesday. See also |
| :meth:`weekday`, :meth:`isocalendar`. |
| |
| |
| .. method:: date.isocalendar() |
| |
| Return a 3-tuple, (ISO year, ISO week number, ISO weekday). |
| |
| The ISO calendar is a widely used variant of the Gregorian calendar. See |
| http://www.phys.uu.nl/ vgent/calendar/isocalendar.htm for a good explanation. |
| |
| 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 |
| ``date(2003, 12, 29).isocalendar() == (2004, 1, 1)`` and ``date(2004, 1, |
| 4).isocalendar() == (2004, 1, 7)``. |
| |
| |
| .. method:: date.isoformat() |
| |
| Return a string representing the date in ISO 8601 format, 'YYYY-MM-DD'. For |
| example, ``date(2002, 12, 4).isoformat() == '2002-12-04'``. |
| |
| |
| .. method:: date.__str__() |
| |
| For a date *d*, ``str(d)`` is equivalent to ``d.isoformat()``. |
| |
| |
| .. method:: date.ctime() |
| |
| Return a string representing the date, for example ``date(2002, 12, |
| 4).ctime() == 'Wed Dec 4 00:00:00 2002'``. ``d.ctime()`` is equivalent to |
| ``time.ctime(time.mktime(d.timetuple()))`` on platforms where the native C |
| :cfunc:`ctime` function (which :func:`time.ctime` invokes, but which |
| :meth:`date.ctime` does not invoke) conforms to the C standard. |
| |
| |
| .. method:: date.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 |
| section :ref:`strftime-behavior`. |
| |
| |
| .. _datetime-datetime: |
| |
| :class:`datetime` Objects |
| ------------------------- |
| |
| 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: |
| |
| |
| .. class:: datetime(year, month, day[, hour[, minute[, second[, microsecond[, tzinfo]]]]]) |
| |
| The year, month and day arguments are required. *tzinfo* may be ``None``, or an |
| instance of a :class:`tzinfo` subclass. The remaining arguments may be ints or |
| longs, in the following ranges: |
| |
| * ``MINYEAR <= year <= MAXYEAR`` |
| * ``1 <= month <= 12`` |
| * ``1 <= day <= number of days in the given month and year`` |
| * ``0 <= hour < 24`` |
| * ``0 <= minute < 60`` |
| * ``0 <= second < 60`` |
| * ``0 <= microsecond < 1000000`` |
| |
| If an argument outside those ranges is given, :exc:`ValueError` is raised. |
| |
| Other constructors, all class methods: |
| |
| |
| .. method:: datetime.today() |
| |
| Return the current local datetime, with :attr:`tzinfo` ``None``. This is |
| equivalent to ``datetime.fromtimestamp(time.time())``. See also :meth:`now`, |
| :meth:`fromtimestamp`. |
| |
| |
| .. method:: datetime.now([tz]) |
| |
| Return the current local date and time. If optional argument *tz* is ``None`` |
| or not specified, this is like :meth:`today`, but, if possible, supplies more |
| precision than can be gotten from going through a :func:`time.time` timestamp |
| (for example, this may be possible on platforms supplying the C |
| :cfunc:`gettimeofday` function). |
| |
| Else *tz* must be an instance of a class :class:`tzinfo` subclass, and the |
| current date and time are converted to *tz*'s time zone. In this case the |
| result is equivalent to ``tz.fromutc(datetime.utcnow().replace(tzinfo=tz))``. |
| See also :meth:`today`, :meth:`utcnow`. |
| |
| |
| .. method:: datetime.utcnow() |
| |
| Return the current UTC date and time, with :attr:`tzinfo` ``None``. This is like |
| :meth:`now`, but returns the current UTC date and time, as a naive |
| :class:`datetime` object. See also :meth:`now`. |
| |
| |
| .. method:: datetime.fromtimestamp(timestamp[, tz]) |
| |
| Return the local date and time corresponding to the POSIX timestamp, such as is |
| returned by :func:`time.time`. If optional argument *tz* is ``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 *tz* must be an instance of a class :class:`tzinfo` subclass, and the |
| timestamp is converted to *tz*'s time zone. In this case the result is |
| equivalent to |
| ``tz.fromutc(datetime.utcfromtimestamp(timestamp).replace(tzinfo=tz))``. |
| |
| :meth:`fromtimestamp` may raise :exc:`ValueError`, if the timestamp is out of |
| the range of values supported by the platform C :cfunc:`localtime` or |
| :cfunc:`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 :meth:`fromtimestamp`, |
| and then it's possible to have two timestamps differing by a second that yield |
| identical :class:`datetime` objects. See also :meth:`utcfromtimestamp`. |
| |
| |
| .. method:: datetime.utcfromtimestamp(timestamp) |
| |
| Return the UTC :class:`datetime` corresponding to the POSIX timestamp, with |
| :attr:`tzinfo` ``None``. This may raise :exc:`ValueError`, if the timestamp is |
| out of the range of values supported by the platform C :cfunc:`gmtime` function. |
| It's common for this to be restricted to years in 1970 through 2038. See also |
| :meth:`fromtimestamp`. |
| |
| |
| .. method:: datetime.fromordinal(ordinal) |
| |
| Return the :class:`datetime` corresponding to the proleptic Gregorian ordinal, |
| where January 1 of year 1 has ordinal 1. :exc:`ValueError` is raised unless ``1 |
| <= ordinal <= datetime.max.toordinal()``. The hour, minute, second and |
| microsecond of the result are all 0, and :attr:`tzinfo` is ``None``. |
| |
| |
| .. method:: datetime.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 :attr:`tzinfo` members are equal to |
| the given :class:`time` object's. For any :class:`datetime` object *d*, ``d == |
| datetime.combine(d.date(), d.timetz())``. If date is a :class:`datetime` |
| object, its time and :attr:`tzinfo` members are ignored. |
| |
| |
| .. method:: datetime.strptime(date_string, format) |
| |
| Return a :class:`datetime` corresponding to *date_string*, parsed according to |
| *format*. This is equivalent to ``datetime(*(time.strptime(date_string, |
| format)[0:6]))``. :exc:`ValueError` is raised if the date_string and format |
| can't be parsed by :func:`time.strptime` or if it returns a value which isn't a |
| time tuple. |
| |
| |
| Class attributes: |
| |
| |
| .. attribute:: datetime.min |
| |
| The earliest representable :class:`datetime`, ``datetime(MINYEAR, 1, 1, |
| tzinfo=None)``. |
| |
| |
| .. attribute:: datetime.max |
| |
| The latest representable :class:`datetime`, ``datetime(MAXYEAR, 12, 31, 23, 59, |
| 59, 999999, tzinfo=None)``. |
| |
| |
| .. attribute:: datetime.resolution |
| |
| The smallest possible difference between non-equal :class:`datetime` objects, |
| ``timedelta(microseconds=1)``. |
| |
| Instance attributes (read-only): |
| |
| |
| .. attribute:: datetime.year |
| |
| Between :const:`MINYEAR` and :const:`MAXYEAR` inclusive. |
| |
| |
| .. attribute:: datetime.month |
| |
| Between 1 and 12 inclusive. |
| |
| |
| .. attribute:: datetime.day |
| |
| Between 1 and the number of days in the given month of the given year. |
| |
| |
| .. attribute:: datetime.hour |
| |
| In ``range(24)``. |
| |
| |
| .. attribute:: datetime.minute |
| |
| In ``range(60)``. |
| |
| |
| .. attribute:: datetime.second |
| |
| In ``range(60)``. |
| |
| |
| .. attribute:: datetime.microsecond |
| |
| In ``range(1000000)``. |
| |
| |
| .. attribute:: datetime.tzinfo |
| |
| The object passed as the *tzinfo* argument to the :class:`datetime` constructor, |
| or ``None`` if none was passed. |
| |
| Supported operations: |
| |
| +---------------------------------------+-------------------------------+ |
| | Operation | Result | |
| +=======================================+===============================+ |
| | ``datetime2 = datetime1 + timedelta`` | \(1) | |
| +---------------------------------------+-------------------------------+ |
| | ``datetime2 = datetime1 - timedelta`` | \(2) | |
| +---------------------------------------+-------------------------------+ |
| | ``timedelta = datetime1 - datetime2`` | \(3) | |
| +---------------------------------------+-------------------------------+ |
| | ``datetime1 < datetime2`` | Compares :class:`datetime` to | |
| | | :class:`datetime`. (4) | |
| +---------------------------------------+-------------------------------+ |
| |
| (1) |
| datetime2 is a duration of timedelta removed from datetime1, moving forward in |
| time if ``timedelta.days`` > 0, or backward if ``timedelta.days`` < 0. The |
| result has the same :attr:`tzinfo` member as the input datetime, and datetime2 - |
| datetime1 == timedelta after. :exc:`OverflowError` is raised if datetime2.year |
| would be smaller than :const:`MINYEAR` or larger than :const:`MAXYEAR`. Note |
| that no time zone adjustments are done even if the input is an aware object. |
| |
| (2) |
| Computes the datetime2 such that datetime2 + timedelta == datetime1. As for |
| addition, the result has the same :attr:`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. |
| |
| (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, :exc:`TypeError` is raised. |
| |
| If both are naive, or both are aware and have the same :attr:`tzinfo` member, |
| the :attr:`tzinfo` members are ignored, and the result is a :class:`timedelta` |
| object *t* such that ``datetime2 + t == datetime1``. No time zone adjustments |
| are done in this case. |
| |
| If both are aware and have different :attr:`tzinfo` members, ``a-b`` acts as if |
| *a* and *b* were first converted to naive UTC datetimes first. The result is |
| ``(a.replace(tzinfo=None) - a.utcoffset()) - (b.replace(tzinfo=None) - |
| b.utcoffset())`` except that the implementation never overflows. |
| |
| (4) |
| *datetime1* is considered less than *datetime2* when *datetime1* precedes |
| *datetime2* in time. |
| |
| If one comparand is naive and the other is aware, :exc:`TypeError` is raised. |
| If both comparands are aware, and have the same :attr:`tzinfo` member, the |
| common :attr:`tzinfo` member is ignored and the base datetimes are compared. If |
| both comparands are aware and have different :attr:`tzinfo` members, the |
| comparands are first adjusted by subtracting their UTC offsets (obtained from |
| ``self.utcoffset()``). |
| |
| .. note:: |
| |
| In order to stop comparison from falling back to the default scheme of comparing |
| object addresses, datetime comparison normally raises :exc:`TypeError` if the |
| other comparand isn't also a :class:`datetime` object. However, |
| ``NotImplemented`` is returned instead if the other comparand has a |
| :meth:`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, :exc:`TypeError` is raised |
| unless the comparison is ``==`` or ``!=``. The latter cases return |
| :const:`False` or :const:`True`, respectively. |
| |
| :class:`datetime` objects can be used as dictionary keys. In Boolean contexts, |
| all :class:`datetime` objects are considered to be true. |
| |
| Instance methods: |
| |
| |
| .. method:: datetime.date() |
| |
| Return :class:`date` object with same year, month and day. |
| |
| |
| .. method:: datetime.time() |
| |
| Return :class:`time` object with same hour, minute, second and microsecond. |
| :attr:`tzinfo` is ``None``. See also method :meth:`timetz`. |
| |
| |
| .. method:: datetime.timetz() |
| |
| Return :class:`time` object with same hour, minute, second, microsecond, and |
| tzinfo members. See also method :meth:`time`. |
| |
| |
| .. method:: datetime.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 ``tzinfo=None`` |
| can be specified to create a naive datetime from an aware datetime with no |
| conversion of date and time members. |
| |
| |
| .. method:: datetime.astimezone(tz) |
| |
| Return a :class:`datetime` object with new :attr:`tzinfo` member *tz*, adjusting |
| the date and time members so the result is the same UTC time as *self*, but in |
| *tz*'s local time. |
| |
| *tz* must be an instance of a :class:`tzinfo` subclass, and its |
| :meth:`utcoffset` and :meth:`dst` methods must not return ``None``. *self* must |
| be aware (``self.tzinfo`` must not be ``None``, and ``self.utcoffset()`` must |
| not return ``None``). |
| |
| If ``self.tzinfo`` is *tz*, ``self.astimezone(tz)`` is equal to *self*: no |
| adjustment of date or time members is performed. Else the result is local time |
| in time zone *tz*, representing the same UTC time as *self*: after ``astz = |
| dt.astimezone(tz)``, ``astz - astz.utcoffset()`` will usually have the same date |
| and time members as ``dt - 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 *tz* models both standard and |
| daylight time). |
| |
| If you merely want to attach a time zone object *tz* to a datetime *dt* without |
| adjustment of date and time members, use ``dt.replace(tzinfo=tz)``. If you |
| merely want to remove the time zone object from an aware datetime *dt* without |
| conversion of date and time members, use ``dt.replace(tzinfo=None)``. |
| |
| Note that the default :meth:`tzinfo.fromutc` method can be overridden in a |
| :class:`tzinfo` subclass to affect the result returned by :meth:`astimezone`. |
| Ignoring error cases, :meth:`astimezone` acts like:: |
| |
| 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) |
| |
| |
| .. method:: datetime.utcoffset() |
| |
| If :attr:`tzinfo` is ``None``, returns ``None``, else returns |
| ``self.tzinfo.utcoffset(self)``, and raises an exception if the latter doesn't |
| return ``None``, or a :class:`timedelta` object representing a whole number of |
| minutes with magnitude less than one day. |
| |
| |
| .. method:: datetime.dst() |
| |
| If :attr:`tzinfo` is ``None``, returns ``None``, else returns |
| ``self.tzinfo.dst(self)``, and raises an exception if the latter doesn't return |
| ``None``, or a :class:`timedelta` object representing a whole number of minutes |
| with magnitude less than one day. |
| |
| |
| .. method:: datetime.tzname() |
| |
| If :attr:`tzinfo` is ``None``, returns ``None``, else returns |
| ``self.tzinfo.tzname(self)``, raises an exception if the latter doesn't return |
| ``None`` or a string object, |
| |
| |
| .. method:: datetime.timetuple() |
| |
| Return a :class:`time.struct_time` such as returned by :func:`time.localtime`. |
| ``d.timetuple()`` is equivalent to ``time.struct_time((d.year, d.month, d.day, |
| d.hour, d.minute, d.second, d.weekday(), d.toordinal() - date(d.year, 1, |
| 1).toordinal() + 1, dst))`` The :attr:`tm_isdst` flag of the result is set |
| according to the :meth:`dst` method: :attr:`tzinfo` is ``None`` or :meth:`dst` |
| returns ``None``, :attr:`tm_isdst` is set to ``-1``; else if :meth:`dst` |
| returns a non-zero value, :attr:`tm_isdst` is set to ``1``; else ``tm_isdst`` is |
| set to ``0``. |
| |
| |
| .. method:: datetime.utctimetuple() |
| |
| If :class:`datetime` instance *d* is naive, this is the same as |
| ``d.timetuple()`` except that :attr:`tm_isdst` is forced to 0 regardless of what |
| ``d.dst()`` returns. DST is never in effect for a UTC time. |
| |
| If *d* is aware, *d* is normalized to UTC time, by subtracting |
| ``d.utcoffset()``, and a :class:`time.struct_time` for the normalized time is |
| returned. :attr:`tm_isdst` is forced to 0. Note that the result's |
| :attr:`tm_year` member may be :const:`MINYEAR`\ -1 or :const:`MAXYEAR`\ +1, if |
| *d*.year was ``MINYEAR`` or ``MAXYEAR`` and UTC adjustment spills over a year |
| boundary. |
| |
| |
| .. method:: datetime.toordinal() |
| |
| Return the proleptic Gregorian ordinal of the date. The same as |
| ``self.date().toordinal()``. |
| |
| |
| .. method:: datetime.weekday() |
| |
| Return the day of the week as an integer, where Monday is 0 and Sunday is 6. |
| The same as ``self.date().weekday()``. See also :meth:`isoweekday`. |
| |
| |
| .. method:: datetime.isoweekday() |
| |
| Return the day of the week as an integer, where Monday is 1 and Sunday is 7. |
| The same as ``self.date().isoweekday()``. See also :meth:`weekday`, |
| :meth:`isocalendar`. |
| |
| |
| .. method:: datetime.isocalendar() |
| |
| Return a 3-tuple, (ISO year, ISO week number, ISO weekday). The same as |
| ``self.date().isocalendar()``. |
| |
| |
| .. method:: datetime.isoformat([sep]) |
| |
| Return a string representing the date and time in ISO 8601 format, |
| YYYY-MM-DDTHH:MM:SS.mmmmmm or, if :attr:`microsecond` is 0, |
| YYYY-MM-DDTHH:MM:SS |
| |
| If :meth:`utcoffset` does not return ``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 :attr:`microsecond` is 0 |
| YYYY-MM-DDTHH:MM:SS+HH:MM |
| |
| The optional argument *sep* (default ``'T'``) is a one-character separator, |
| placed between the date and time portions of the result. For example, :: |
| |
| >>> 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' |
| |
| |
| .. method:: datetime.__str__() |
| |
| For a :class:`datetime` instance *d*, ``str(d)`` is equivalent to |
| ``d.isoformat(' ')``. |
| |
| |
| .. method:: datetime.ctime() |
| |
| Return a string representing the date and time, for example ``datetime(2002, 12, |
| 4, 20, 30, 40).ctime() == 'Wed Dec 4 20:30:40 2002'``. ``d.ctime()`` is |
| equivalent to ``time.ctime(time.mktime(d.timetuple()))`` on platforms where the |
| native C :cfunc:`ctime` function (which :func:`time.ctime` invokes, but which |
| :meth:`datetime.ctime` does not invoke) conforms to the C standard. |
| |
| |
| .. method:: datetime.strftime(format) |
| |
| Return a string representing the date and time, controlled by an explicit format |
| string. See section :ref:`strftime-behavior`. |
| |
| |
| .. _datetime-time: |
| |
| :class:`time` Objects |
| --------------------- |
| |
| A time object represents a (local) time of day, independent of any particular |
| day, and subject to adjustment via a :class:`tzinfo` object. |
| |
| |
| .. class:: time(hour[, minute[, second[, microsecond[, tzinfo]]]]) |
| |
| All arguments are optional. *tzinfo* may be ``None``, or an instance of a |
| :class:`tzinfo` subclass. The remaining arguments may be ints or longs, in the |
| following ranges: |
| |
| * ``0 <= hour < 24`` |
| * ``0 <= minute < 60`` |
| * ``0 <= second < 60`` |
| * ``0 <= microsecond < 1000000``. |
| |
| If an argument outside those ranges is given, :exc:`ValueError` is raised. All |
| default to ``0`` except *tzinfo*, which defaults to :const:`None`. |
| |
| Class attributes: |
| |
| |
| .. attribute:: time.min |
| |
| The earliest representable :class:`time`, ``time(0, 0, 0, 0)``. |
| |
| |
| .. attribute:: time.max |
| |
| The latest representable :class:`time`, ``time(23, 59, 59, 999999)``. |
| |
| |
| .. attribute:: time.resolution |
| |
| The smallest possible difference between non-equal :class:`time` objects, |
| ``timedelta(microseconds=1)``, although note that arithmetic on :class:`time` |
| objects is not supported. |
| |
| Instance attributes (read-only): |
| |
| |
| .. attribute:: time.hour |
| |
| In ``range(24)``. |
| |
| |
| .. attribute:: time.minute |
| |
| In ``range(60)``. |
| |
| |
| .. attribute:: time.second |
| |
| In ``range(60)``. |
| |
| |
| .. attribute:: time.microsecond |
| |
| In ``range(1000000)``. |
| |
| |
| .. attribute:: time.tzinfo |
| |
| The object passed as the tzinfo argument to the :class:`time` constructor, or |
| ``None`` if none was passed. |
| |
| Supported operations: |
| |
| * comparison of :class:`time` to :class:`time`, where *a* is considered less |
| than *b* when *a* precedes *b* in time. If one comparand is naive and the other |
| is aware, :exc:`TypeError` is raised. If both comparands are aware, and have |
| the same :attr:`tzinfo` member, the common :attr:`tzinfo` member is ignored and |
| the base times are compared. If both comparands are aware and have different |
| :attr:`tzinfo` members, the comparands are first adjusted by subtracting their |
| UTC offsets (obtained from ``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, |
| :exc:`TypeError` is raised unless the comparison is ``==`` or ``!=``. The |
| latter cases return :const:`False` or :const:`True`, respectively. |
| |
| * hash, use as dict key |
| |
| * efficient pickling |
| |
| * in Boolean contexts, a :class:`time` object is considered to be true if and |
| only if, after converting it to minutes and subtracting :meth:`utcoffset` (or |
| ``0`` if that's ``None``), the result is non-zero. |
| |
| Instance methods: |
| |
| |
| .. method:: time.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 ``tzinfo=None`` |
| can be specified to create a naive :class:`time` from an aware :class:`time`, |
| without conversion of the time members. |
| |
| |
| .. method:: time.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 :meth:`utcoffset` does not return ``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 |
| |
| |
| .. method:: time.__str__() |
| |
| For a time *t*, ``str(t)`` is equivalent to ``t.isoformat()``. |
| |
| |
| .. method:: time.strftime(format) |
| |
| Return a string representing the time, controlled by an explicit format string. |
| See section :ref:`strftime-behavior`. |
| |
| |
| .. method:: time.utcoffset() |
| |
| If :attr:`tzinfo` is ``None``, returns ``None``, else returns |
| ``self.tzinfo.utcoffset(None)``, and raises an exception if the latter doesn't |
| return ``None`` or a :class:`timedelta` object representing a whole number of |
| minutes with magnitude less than one day. |
| |
| |
| .. method:: time.dst() |
| |
| If :attr:`tzinfo` is ``None``, returns ``None``, else returns |
| ``self.tzinfo.dst(None)``, and raises an exception if the latter doesn't return |
| ``None``, or a :class:`timedelta` object representing a whole number of minutes |
| with magnitude less than one day. |
| |
| |
| .. method:: time.tzname() |
| |
| If :attr:`tzinfo` is ``None``, returns ``None``, else returns |
| ``self.tzinfo.tzname(None)``, or raises an exception if the latter doesn't |
| return ``None`` or a string object. |
| |
| |
| .. _datetime-tzinfo: |
| |
| :class:`tzinfo` Objects |
| ----------------------- |
| |
| :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 :mod:`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 |
| :meth:`__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 |
| :mod:`datetime` objects. If in doubt, simply implement all of them. |
| |
| |
| .. method:: tzinfo.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, :meth:`utcoffset` should return their sum. If |
| the UTC offset isn't known, return ``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 :meth:`utcoffset` will probably look |
| like one of these two:: |
| |
| return CONSTANT # fixed-offset class |
| return CONSTANT + self.dst(dt) # daylight-aware class |
| |
| If :meth:`utcoffset` does not return ``None``, :meth:`dst` should not return |
| ``None`` either. |
| |
| The default implementation of :meth:`utcoffset` raises |
| :exc:`NotImplementedError`. |
| |
| |
| .. method:: tzinfo.dst(self, dt) |
| |
| Return the daylight saving time (DST) adjustment, in minutes east of UTC, or |
| ``None`` if DST information isn't known. Return ``timedelta(0)`` if DST is not |
| in effect. If DST is in effect, return the offset as a :class:`timedelta` object |
| (see :meth:`utcoffset` for details). Note that DST offset, if applicable, has |
| already been added to the UTC offset returned by :meth:`utcoffset`, so there's |
| no need to consult :meth:`dst` unless you're interested in obtaining DST info |
| separately. For example, :meth:`datetime.timetuple` calls its :attr:`tzinfo` |
| member's :meth:`dst` method to determine how the :attr:`tm_isdst` flag should be |
| set, and :meth:`tzinfo.fromutc` calls :meth:`dst` to account for DST changes |
| when crossing time zones. |
| |
| An instance *tz* of a :class:`tzinfo` subclass that models both standard and |
| daylight times must be consistent in this sense: |
| |
| ``tz.utcoffset(dt) - tz.dst(dt)`` |
| |
| must return the same result for every :class:`datetime` *dt* with ``dt.tzinfo == |
| 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 :meth:`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 |
| :meth:`tzinfo.fromutc` to work correctly with :meth:`astimezone` regardless. |
| |
| Most implementations of :meth:`dst` will probably look like one of these two:: |
| |
| def dst(self): |
| # a fixed-offset class: doesn't account for DST |
| return timedelta(0) |
| |
| or :: |
| |
| def dst(self): |
| # 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) |
| |
| The default implementation of :meth:`dst` raises :exc:`NotImplementedError`. |
| |
| |
| .. method:: tzinfo.tzname(self, dt) |
| |
| Return the time zone name corresponding to the :class:`datetime` object *dt*, as |
| a string. Nothing about string names is defined by the :mod:`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 ``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 *dt* passed, especially if the :class:`tzinfo` class is accounting for |
| daylight time. |
| |
| The default implementation of :meth:`tzname` raises :exc:`NotImplementedError`. |
| |
| 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 ``None`` as the |
| argument. A :class:`tzinfo` subclass's methods should therefore be prepared to |
| accept a *dt* argument of ``None``, or of class :class:`datetime`. |
| |
| When ``None`` is passed, it's up to the class designer to decide the best |
| response. For example, returning ``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 ``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, ``dt.tzinfo`` is the same object as *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 *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: |
| |
| |
| .. method:: tzinfo.fromutc(self, dt) |
| |
| This is called from the default :class:`datetime.astimezone()` implementation. |
| When called from that, ``dt.tzinfo`` is *self*, and *dt*'s date and time members |
| are to be viewed as expressing a UTC time. The purpose of :meth:`fromutc` is to |
| adjust the date and time members, returning an equivalent datetime in *self*'s |
| local time. |
| |
| Most :class:`tzinfo` subclasses should be able to inherit the default |
| :meth:`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 :meth:`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 :meth:`astimezone` and |
| :meth:`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 :meth:`fromutc` implementation acts |
| like:: |
| |
| 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 |
| |
| Example :class:`tzinfo` classes: |
| |
| .. literalinclude:: ../includes/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:: |
| |
| 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 |
| |
| 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 |
| ``astimezone(Eastern)`` won't deliver a result with ``hour == 2`` on the day DST |
| begins. In order for :meth:`astimezone` to make this guarantee, the |
| :meth:`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. |
| :meth:`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 |
| :meth:`astimezone` to make this guarantee, the :meth:`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)). |
| |
| |
| .. _strftime-behavior: |
| |
| :meth:`strftime` Behavior |
| ------------------------- |
| |
| :class:`date`, :class:`datetime`, and :class:`time` objects all support a |
| ``strftime(format)`` method, to create a string representing the time under the |
| control of an explicit format string. Broadly speaking, ``d.strftime(fmt)`` |
| acts like the :mod:`time` module's ``time.strftime(fmt, d.timetuple())`` |
| although not all objects support a :meth:`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, ``1900`` |
| is substituted for the year, and ``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, ``0`` is substituted for them. |
| |
| For a naive object, the ``%z`` and ``%Z`` format codes are replaced by empty |
| strings. |
| |
| For an aware object: |
| |
| ``%z`` |
| :meth:`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 |
| :meth:`utcoffset` returns ``timedelta(hours=-3, minutes=-30)``, ``%z`` is |
| replaced with the string ``'-0330'``. |
| |
| ``%Z`` |
| If :meth:`tzname` returns ``None``, ``%Z`` is replaced by an empty string. |
| Otherwise ``%Z`` is replaced by the returned value, which must be a string. |
| |
| The full set of format codes supported varies across platforms, because Python |
| calls the platform C library's :func:`strftime` function, and platform |
| variations are common. The documentation for Python's :mod:`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 :meth:`strftime` works also varies across |
| platforms. Regardless of platform, years before 1900 cannot be used. |
| |
| .. % %% This example is obsolete, since strptime is now supported by datetime. |
| .. % |
| .. % \subsection{Examples} |
| .. % |
| .. % \subsubsection{Creating Datetime Objects from Formatted Strings} |
| .. % |
| .. % The \class{datetime} class does not directly support parsing formatted time |
| .. % strings. You can use \function{time.strptime} to do the parsing and create |
| .. % a \class{datetime} object from the tuple it returns: |
| .. % |
| .. % \begin{verbatim} |
| .. % >>> s = "2005-12-06T12:13:14" |
| .. % >>> from datetime import datetime |
| .. % >>> from time import strptime |
| .. % >>> datetime(*strptime(s, "%Y-%m-%dT%H:%M:%S")[0:6]) |
| .. % datetime.datetime(2005, 12, 6, 12, 13, 14) |
| .. % \end{verbatim} |
| .. % |
| |