[Datetime-SIG] Timeline arithmetic?

[Carl Meyer]

[Guido]
> OK. I'll just remember "model A bad, model B good." :-)

Fine by me. :-)

> Or, perhaps more fairly, "model A is how pytz thinks, model B is how the
> stdlib thinks."

We'd be in better shape if it were that simple. pytz is strictly model
A. Unfortunately the stdlib isn't consistent in how it thinks (short
version: because __hash__ and cross-timezone equality and arithmetic
implicitly treat aware datetimes as if they were unambiguous model A
instants, when they aren't), and that's the root of all the difficulty
with PEP 495.

(I can give a longer explanation of _why_ that causes difficulty with
PEP 495 if you want it, or you can go back and read the last few threads
in detail, or you can just wait for the PEP :-) ).

Carl

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