diff --git a/Doc/library/datetime.rst b/Doc/library/datetime.rst index 8be8974a41f..7baf9875397 100644 --- a/Doc/library/datetime.rst +++ b/Doc/library/datetime.rst @@ -17,16 +17,23 @@ focus of the implementation is on efficient attribute 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), +There are two kinds of date and time objects: "naive" and "aware". + +An aware object has sufficient knowledge of applicable algorithmic and +political time adjustments, such as time zone and daylight saving time +information, to locate itself relative to other aware objects. An aware object +is used to represent a specific moment in time that is not open to +interpretation [#]_. + ++A naive object does not contain enough information to unambiguously locate ++itself relative to other date/time objects. Whether +a naive 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 +miles, or mass. Naive 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 +For applications requiring aware objects, :class:`.datetime` and :class:`.time` objects have an optional time zone information attribute, :attr:`tzinfo`, that can be set to an instance of a subclass of the abstract :class:`tzinfo` class. These :class:`tzinfo` objects capture information about the offset from UTC time, the @@ -105,10 +112,13 @@ 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. +An object of type :class:`.time` or :class:`.datetime` may be naive or aware. +A :class:`.datetime` object *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. A :class:`.time` object *t* is aware +if ``t.tzinfo`` is not ``None`` and ``t.tzinfo.utcoffset(None)`` does not return +``None``. Otherwise, *t* is naive. The distinction between naive and aware doesn't apply to :class:`timedelta` objects. @@ -1707,3 +1717,8 @@ Notes: (5) For example, if :meth:`utcoffset` returns ``timedelta(hours=-3, minutes=-30)``, ``%z`` is replaced with the string ``'-0330'``. + + +.. rubric:: Footnotes + +.. [#] If, that is, we ignore the effects of Relativity