[Datetime-SIG] What's are the issues?

[Felipe Ochoa]

In the interest of continuing to lay the foundation for discussion, let me
build on Chris's recap before giving my viewpoint on the issue:


1. Datetime arithmetic
>>     a) datetime +/- timedelta
>>         ii. Aware (with tzinfo) datetime objects
>
> If the math is done in UTC, then there is no issue, yes? the timedelta is
> added or subtracted, and the result has the same tzinfo object.


If I've understood correctly, this is one of the bigger points of
contention. Specifically, the following operation is quite polarizing:
`datetime(2015, 3, 7, 13, 0, tzinfo=zoneinfo('America/New_York') ) +
timedelta(days=1)`

It raises the following two questions:
* Should `days=1` be interpreted the same as `hours=24`?
* If it is interpreted the same, should the addition be "naive" (not
adjusting for the jump from 1:59 to 3:00) or "aware"

Current semantics call for the answers to be "yes" and "naive"


>     b) datetime - datetime
>
>         ii. When both have same tzinfo
>
> Just do the math. Store as UTC makes it easy. return a timedelta.


This is another contentious issue. What do you want `datetime(2015, 3, 8,
13, tzinfo=zoneinfo('America/New_York')) - datetime(2015, 3, 7, 13,
tzinfo=zoneinfo('America/New_York'))` to be? There's a camp for
`timedelta(seconds=24 * 60 * 60)` and a camp for `timedelta(seconds=23 * 60
* 60)`, though I think everyone agrees that `(dt + delta) - dt == delta` is
necessary.

2. Inter-timezone conversion
>
>     b) algorithm specification
>
> what part of the algorithm? seems pretty straightforward to me (the
> algorithm, anyway)


I'm less clear on the issue here, but Isaac seemed to disagree with the
algorithm in datetime.py (
https://hg.python.org/cpython/file/v3.5.0b1/Lib/datetime.py#l1935) [
http://code.activestate.com/lists/python-dev/137300/]
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