[Python-checkins] cpython (3.2): #14766: Add correct algorithm for when a 'time' object is naive.

[r.david.murray]

http://hg.python.org/cpython/rev/28ed782949f9
changeset:   76937:28ed782949f9
branch:      3.2
parent:      76935:ffe39fba03ae
user:        R David Murray <rdmurray at bitdance.com>
date:        Mon May 14 22:14:46 2012 -0400
summary:
  #14766: Add correct algorithm for when a 'time' object is naive.

This patch also clarifies the definition of Naive and Aware.

Original patch by Greg Weller, I modified the first hunk
somewhat to make the exposition even clearer (I hope).

files:
  Doc/library/datetime.rst |  38 +++++++++++++++++++--------
  1 files changed, 26 insertions(+), 12 deletions(-)


diff --git a/Doc/library/datetime.rst b/Doc/library/datetime.rst
--- a/Doc/library/datetime.rst
+++ b/Doc/library/datetime.rst
@@ -15,16 +15,23 @@
 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
@@ -32,8 +39,8 @@
 one concrete :class:`tzinfo` class, the :class:`timezone` class, is supplied by the
 :mod:`datetime` module.  The :class:`timezone` class can represent simple
 timezones with fixed offset from UTC such as UTC itself or North American EST and
-EDT timezones.  Supporting timezones at whatever level of detail is
-required is up to the application.  The rules for time adjustment across the
+EDT timezones.  Supporting timezones at deeper levels of detail is
+up to the application.  The rules for time adjustment across the
 world are more political than rational, change frequently, and there is no
 standard suitable for every application aside from UTC.
 
@@ -114,10 +121,13 @@
 
 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.
@@ -1806,3 +1816,7 @@
    When the ``%z`` directive is provided to the :meth:`strptime` method, an
    aware :class:`.datetime` object will be produced.  The ``tzinfo`` of the
    result will be set to a :class:`timezone` instance.
+
+.. rubric:: Footnotes
+
+.. [#] If, that is, we ignore the effects of Relativity

-- 
Repository URL: http://hg.python.org/cpython