[Python-Dev] Issue 2736: datetimes and Unix timestamps (original) (raw)

Guido van Rossum guido at python.org
Mon Jun 4 21:05:10 CEST 2012

On Mon, Jun 4, 2012 at 11:46 AM, Alexander Belopolsky <alexander.belopolsky at gmail.com> wrote:

On Mon, Jun 4, 2012 at 1:12 PM, Guido van Rossum <guido at python.org> wrote:

...  I heard a colleague complain that he'd lost several hours trying to figure out how to determine whether two datetimes were within 24h of each other, getting confused by what was happening when the two were on different sides of a DST transition (or worse, in the middle of one). I don't think this is a problem that a general purpose module such as datetime can resolve.  Assuming that all instances are timezone aware, either of the following tests may be appropriate for a given application: 1) dt1 - dt2 == timedelta(1) 2) dt1.date() - dt2.date() == timedelta(1) and dt1.time() == dt2.time() If your application deals with physical processes - (1) may be appropriate, but if it deals with human schedules - (2) may be appropriate.

You seem to have misread -- I don't want to check if they are exactly 24 hours apart. I want to check if they are at most 24 hours apart. The timezone can be assumed to be the same on dt1 and dt2.

A variant of (1) was what was needed -- the user had just confused themselves into thinking they needed to convert to UTC first, and done a poor job of that. This is a common situation.

The only right solution is to lobby your government to abandon the DST.

That's not helping.

-- --Guido van Rossum (python.org/~guido)

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