[Datetime-SIG] Timeline arithmetic?

Tim Peters tim.peters at gmail.com
Mon Sep 7 19:28:25 CEST 2015

> FYI, I am still completely overwhelmed by this discussion.

I recommend that you skip any message with "timeline" in the Subject
line ;-)  Nobody is actually arguing to make timeline arithmetic
(beyond what already exists) any part of PEP 495.  But this is a
"datetime" SIG, not a "PEP 495" SIG, so it's fair game to discuss it

> I will wait until Tim and Alexander tell me there's a PEP to review and
> then I'll read that. Carl: if you feel your position is not represented in that
> PEP (even under "rejected alternatives") I recommend that you write
> your own PEP. But I really hope that you all will come to an agreement
> without competing PEPs!

Short course:  Carl prefers timeline arithmetic, but is not trying to
change anything about what Python's datetime does by default.  He
would like a new kind of tzinfo that simultaneously fixes the
conversion endcases _and_ forces use of timeline arithmetic for all
operations  Current code would neither be hurt nor helped, only code
using the new tzinfos would see any difference.  But current code
trying to use a new tzinfo could break anywhere it relied on classic

While I'm not entirely sure, best guess is that Carl would also prefer
that 495 not be implemented.  But his new kind of tzinfo could be
implemented regardless.  They don't really compete, except in the
eternal battle over theoretical purity ;-)

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