[Datetime-SIG] Clearing up terminology

[Tim Peters]

[Tim, to Guido]
> Do you really intend that we use all three:  "classic arithmetic",
> "human arithmetic", and "strict arithmetic"?.  If so, I don't grasp
> the intended distinction between "classic" and "human".(both seem to
> be the same as what I've been calling "naive arithmetic":  the
> arithmetic Python currently implements for binary arithmetic operators
> involving at least one datetime object).

I _think_ I've divined the intent now:

- "classic arithmetic":  what Python datetime arithmetic currently does

- "strict arithmetic":  aka timeline arithmetic, what Lennart wants

- "human arithmetic"  aka "calendar operations" - including at least
relative deltas involving units (like months and years) which have no
fixed meaning in naive time  This intersects with "classic arithmetic"
(current "datetime +- timedelta"). but unlike those cases of classic
arithmetic is intended to cover both the "naive" and "UTC timeline"
models of time.  For example, there "should be" a way to spell "an
hour from now" that follows "strict arithmetic" rules when the
datetime is aware.

Or not ;-)