[Datetime-SIG] Are there any "correct" implementations of tzinfo?

Laura Creighton lac at openend.se
Mon Sep 14 10:53:09 CEST 2015

In a message of Sun, 13 Sep 2015 15:21:45 -0700, Guido van Rossum writes:
>Hi Laura!
>Wouldn't it be sufficient for people in Creighton to set their timezone to
>US/Central? IIUC the Canadian DST rules are the same as the US ones. Now,
>the question may remain how do people know what to set their timezone to.
>But neither pytz nor datetime can help with that -- it is up to the

The Canadian DST rules are not the same as the US ones, wherein lies
the rub.  The province of Saskatchewan has a few areas which prefer to
be on Mountain time, which we will ignore in this mail.  The bulk of
them prefer to be on Central time, which is the same as Winnipeg and
Chicago.  But what happens on DST start day (early March) in
Saskachewan?  Provincial law mandates that you do not change your
clock, and do not adopt daylight savings time.  The people in
Saskachewan thus stick to CST all year round.  And this is how
sites like http://www.timeanddate.com/worldclock/canada/saskatoon
record things, with them at CST.

However, the people of Creighton have decided to keep DST, in
violation of the law, so they set their clocks forward.
http://www.timeanddate.com/worldclock/canada/creighton does this
properly as well, showing them with CDT.

But this is not quite the complete story.  In many (most?) places in
Saskatchewan, the rule is understood differently.  Instead of 'we keep
to CST all year long' is is understood that  'we keep central time in
the winter and mountain time in the summer'.

This makes parsing log files from all over Saskachewan, where sometime
in March things often stop saying CST and say MDT instead rather more
interesting than the adverage person might suspect.


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