[issue13466] new timezones

[Amaury Forgeot d'Arc]

Amaury Forgeot d'Arc <amauryfa at gmail.com> added the comment:

> A fairly "correct" way is to query the time zone database at time module
> import time by using the DST and GMT offset of that time.

But that does not give the *other* timezone :-(

> IMO time.timezone and time.daylight should be deprecated since they
> will give wrong results around DST changes (both switch times and
> legal changes such as the described one) in long running processes
> such as daemons.

time.timezone is the non-DST timezone: this value does not change around
the DST change date.  That's why the current implementation uses "absolute"
dates like the of January: DST changes are often in March and October.

What about this algorithm:
- pick the first of January and the first of July surrounding the current date
- if both have tm_idst==0, the region has no DST. Use the current GMT offset for
  both timezone and altzone; daylight=0
- otherwise, use the *current* time and get its DST and GMT offset. This is enough
to compute both timezone and altzone (with the relation altzone=timezone-3600)

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<http://bugs.python.org/issue13466>
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