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.
find a more elegant algorithm (OTOH, the hairy new implementation allows
user-written tzinfo classes to be elegant, so it's a big win even if
astimezone() remains hairy).
Darn! I've only got 10 minutes left to get falling-down drunk! I suppose
I'll have to smoke crack instead now.
an idea from Guido. This restores that the datetime implementation
never passes a datetime d to a tzinfo method unless d.tzinfo is the
tzinfo instance whose method is being called. That in turn allows
enormous simplifications in user-written tzinfo classes (see the Python
sandbox US.py and EU.py for fully fleshed-out examples).
d.astimezone(tz) also raises ValueError now if d lands in the one hour
of the year that can't be expressed in tz (this can happen iff tz models
both standard and daylight time). That it used to return a nonsense
result always ate at me, and it turned out that it seemed impossible to
force a consistent nonsense result under the new implementation (which
doesn't know anything about how tzinfo classes implement their methods --
it can only infer properties indirectly). Guido doesn't like this --
expect it to change.
New tests of conversion between adjacent DST-aware timezones don't pass
yet, and are commented out.
Running the datetime tests in a loop under a debug build leaks 9
references per test run, but I don't believe the datetime code is the
cause (it didn't leak the last time I changed the C code, and the leak
is the same if I disable all the tests that invoke the only function
that changed here). I'll pursue that next.
make the callers figure out the right tzinfo arguments to pass, instead of
making the callees guess. The code is uglier this way, but it's less
brittle (when the callee guesses, the caller can get surprised).
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.
be trusted with years before 1900, so now we raise ValueError if a date or
datetime or datetimetz .strftime() method is called with a year before
1900.
such that the datetime tests failed if the envar PYTHON2K was set.
This is an utter mess, and the datetime module's strftime functions
inherit it. I suspect that, regardless of the PYTHON2K setting, and
regardless of platform limitations, the datetime strftime wrappers
will end up delivering nonsense results (or bogus exceptions) for
any year before 1900. I should probably just refuse to accept years
earlier than that -- else we'll have to implement strftime() by hand.
{timetz,datetimetz}.{utcoffset,dst}() now return a timedelta (or None)
instead of an int (or None).
tzinfo.{utcoffset,dst)() can now return a timedelta (or an int, or None).
Curiously, this was much easier to do in the C implementation than in the
Python implementation (which lives in the Zope3 code tree) -- the C code
already had lots of hair to extract C ints from offset objects, and used
C ints internally.
used that.
wrap_strftime(): Removed the most irritating uses of buf.
TestDate.test_ordinal_conversions(): The C implementation is fast enough
that we can afford to check the endpoints of every year. Also added
tm_yday tests at the endpoints.
Tim Peters
Neal Norwitz
Jack Jansen
Guido van Rossum