[Python-ideas] Please reconsider the Boolean evaluation of midnight

[Donald Stufft]

On Mar 6, 2014, at 11:50 AM, Tim Peters <tim.peters at gmail.com> wrote:

> [Bruce Leban <bruce at leapyear.org>]
>>>> ...
>>>> Just because you wrote the docs doesn't mean you know what they mean to
>>>> other readers. The point of documentation is to explain it to someone
>>>> who doesn't know what it does after all.
> 
> [Tim]
>>> Of course.  What's your point here?
> 
> [Alexander Belopolsky <alexander.belopolsky at gmail.com>]
>> I am with Bruce here.  I tried to digest your notes on timezone algebra [1]
>> for years and I still don't understand it.
>> 
>> [1] http://hg.python.org/cpython/file/b07400659dba/Lib/datetime.py#l1922
> 
> But those aren't user docs - they're notes for developers who are
> deeply steeped in internal details.  And they're hard!  Mucking with
> "all possible" time zones raises mountains of excruciatingly subtle
> details and corner cases.  The masses of tedious "algebra" were needed
> to justify how the internals get away with doing "so little" - and to
> explain why the code still wouldn't work right in all cases if the
> "standard offset" of a single time zone changed (or changes) over
> time.
> 
> Do you claim you still don't understand when bool(time) returns True
> and False?  Those are user docs.  I don't claim that reading them will
> make anyone feel good ;-), but I do believe the computation is
> described clearly enough to enable a reasonable user to predict the
> result in all cases.

I don’t think a reasonable user would predict that midnight UTC in a timezone
with a UTC offset of +5 would be false, while midnight UTC in a timezone with
a UTC offset of -5 would not be false.

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-----------------
Donald Stufft
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