__ne__ no longer complain if they don't know how to compare to the other
thing. If no meaningful way to compare is known, saying "not equal" is
sensible. This allows things like
if adatetime in some_sequence:
and
somedict[adatetime] = whatever
to work as expected even if some_sequence contains non-datetime objects,
or somedict non-datetime keys, because they only call __eq__.
It still complains (raises TypeError) for mixed-type comparisons in
contexts that require a total ordering, such as list.sort(), use as a
key in a BTree-based data structure, and cmp().
compare against "the other" argument, we raise TypeError,
in order to prevent comparison from falling back to the
default (and worse than useless, in this case) comparison
by object address.
That's fine so far as it goes, but leaves no way for
another date/datetime object to make itself comparable
to our objects. For example, it leaves Marc-Andre no way
to teach mxDateTime dates how to compare against Python
dates.
Discussion on Python-Dev raised a number of impractical
ideas, and the simple one implemented here: when we don't
know how to compare against "the other" argument, we raise
TypeError *unless* the other object has a timetuple attr.
In that case, we return NotImplemented instead, and Python
will give the other object a shot at handling the
comparison then.
Note that comparisons of time and timedelta objects still
suffer the original problem, though.
This gives much the same treatment to datetime.fromtimestamp(stamp, tz) as
the last batch of checkins gave to datetime.now(tz): do "the obvious"
thing with the tz argument instead of a senseless thing.
tzinfo.fromutc() method. The C code doesn't implement any of this
yet (well, not the C code on the machine I'm using now), nor does
the test suite reflect it. The Python datetime.py implementation and
test suite in the sandbox do match these doc changes. The C
implementation probably won't catch up before Thursday (Wednesday is
a scheduled "black hole" day this week <0.4 wink>).
When daylight time ends, an hour repeats on the local clock (for example,
in US Eastern, the clock jumps from 1:59 back to 1:00 again). Times in
the repeated hour are ambiguous. A tzinfo subclass that wants to play
with astimezone() needs to treat times in the repeated hour as being
standard time. astimezone() previously required that such times be
treated as daylight time. There seems no killer argument either way,
but Guido wants the standard-time version, and it does seem easier the
new way to code both American (local-time based) and European (UTC-based)
switch rules, and the astimezone() implementation is simpler.
WARNING: It would be a minor miracle if the LaTeX stuff still worked.
s/field/member/ generally everywhere, to conform with most other usage in
the docs.
s/daylight savings time/daylight saving time/ generally everywhere,
because the latter spelling is anally correct.
cases, plus even tougher tests of that. This implementation follows
the correctness proof very closely, and should also be quicker (yes,
I wrote the proof before the code, and the code proves the proof <wink>).
(or None) now. In 2.3a1 they could also return an int or long, but that
was an unhelpfully redundant leftover from an earlier version wherein
they couldn't return a timedelta. TOOWTDI.
suggestion from Guido, along with a formal correctness proof of the
trickiest bit. The intricacy of the proof reveals how delicate this
is, but also how robust the conclusion: correctness doesn't rely on
dst() returning +- one hour (not all real time zones do!), it only
relies on:
1. That dst() returns a (any) non-zero value if and only if daylight
time is in effect.
and
2. That the tzinfo subclass implements a consistent notion of time zone.
The meaning of "consistent" was a hidden assumption, which is now an
explicit requirement in the docs. Alas, it's an unverifiable (by the
datetime implementation) requirement, but so it goes.
docs. Replaced it with an XXX block, because the hoped-for treatment
of DST endcases remains unclear (Guido doesn't really like raising an
exception when it's impossible to deliver a correct result, but so
far I have no way in hand to consistently deliver a defined incorrect
result either).
of the timetz case. A tzinfo method will always see a datetimetz arg,
or None, now. In the former case, it's still possible that it will get
a datetimetz argument belonging to a different timezone. That will get
fixed next.
operands have identical tzinfo members (meaning object identity -- "is").
I misunderstood the intent here, reading wrong conclusion into
conflicting clues.
Fred Drake
Raymond Hettinger
Tim Peters
Andrew M. Kuchling
Neal Norwitz
Guido van Rossum