[Python-Dev] Status on PEP-431 Timezones

Lennart Regebro regebro at gmail.com
Tue Jul 28 14:35:22 CEST 2015

On Tue, Jul 28, 2015 at 1:55 PM, Mark Lawrence <breamoreboy at yahoo.co.uk> wrote:
> One week == 7 days == 7 * 24 hours
> Two weeks = 2 * (one week)

Right, and that of course is not true in actual reality. I know you
are not interested in DST, but with a timezone that has DST, two times
a year, the above statement is wrong.

> As I've said elsewhere I've no interest in DST, at least right here, right
> now, let alone leap seconds. When I run my cashflow forecast the balance in
> my bank account one year from today isn't going to be influenced by UK
> clocks falling back to GMT at the end of October and on to BST at the end of
> next March.

And then you should not use timezoned datetimes, but use naive ones.
If you don't care about the timezone, then don't use it. Problem solved.

It should be noted here that Python is one of the few languages that
actually lets you do that. It's not very common to support time zone
naive datetimes.

> Correct.  What I would like to know is how many people are in my position,
> how many people are in the situation of needing every possible combination
> of dates, times, daylight saving, local time zone rules and anything else
> you can think of under the sun, and how many are on the scale somewhere in
> between these two extremes.

There are a few positions.

1. Not caring. datetime supports that as of today. This is probably
the most common case. That certainly is the case for me most of the
time I need to do something with datetimes. It's usually measuring a
few seconds of time or calculating dates.

2. Caring about time zones including DST's. IMO, this is the most
common case once you care about time zones. You have several time
zones, and you want conversion between them to work, and if you say
one hour, you mean one hour. Datetime as of today does not support
this, and Tim has declared that it never will, at least not before
Python 4 (which amounts to much the same thing).

3. The position of Tim and Guido, which is "I want my time zone aware
datetimes to ignore the time zone, except when converting to other
time zones". I have yet to see a use case for that, and hence I am
still not convinced that this position is useful, I think it is only
based on misunderstanding.

4. ? Are there more positions, something I have missed?


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