[Zope3-dev] RE: [Python-Dev] Holes in time

[Tim Peters]

[Aahz]
> What exactly do you mean by "wall time"?  Is it supposed to be a
> timezone-less value?

The diagram in the original gave agonizingly detailed answers to these
questions.  US Eastern as a tzinfo class tries to combine both EDT and EST;
please read the original msg again, and note that the two "wall time" lines
in the diagram show what US Eastern displays at all the relevant UTC times.

> If yes, you can't convert between wall time and any timezone-based
> value without specifying the time zone the wall clock lives in,
> which has to be relative to UTC.

See the original; the relationship to UTC was explicit at all points there.

> This only becomes a serious problem for round-trip conversions.

The major problem here was in one-way conversion; see the original; two-way
conversion T1 -> T2 -> T1 is impossible if the time in T1 can't be
represented at all in T2 (which is the case here).

> Does it make any sense to include a flag if a time value ever gets
> converted between wall time and any other kind of time?
>
> Every other datetime package seems to live with the
> wiggle involved in round-trip conversions, why not Python?

Round-trip conversions aren't at issue here, except to the extent that the
"unspellable hour" at the end of DST makes some one-way conversions
impossible.