Re: First time of the day

Eric Brine wrote:
>I posted a solution here:
>http://stackoverflow.com/a/20850899/589924

That message states

|On the DateTime mailing list, Zefram suggested I do a binary search on
|the time zone data. The following is an implementation of that solution:

which is not correct.  I did not suggest searching among observance
spans, as the code there does.  I suggested searching among UT times.
Please post a correction.

>I perform a binary search of the tz's spans, looking at the *local* times.

This is a valid approach *if* you have access to the span data itself.
The code you posted on stackoverflow uses the internals of the current
DT:TZ implementation.  The public API for DT:TZ objects doesn't support
this.  That's (in part) why I suggested an algorithm that only accesses
zone data in the form of UT->local conversions.

>*I made one assumption*: There is no dt to which one can add time to obtain
>a dt with an earlier date.

That's the same assumption I made, which I reckon is justified by the
Olson database.

-zefram