Daylight Savings Time transition broken

[Tom Grigg <tomegrigg@…>]

The POSIX timezone implementation in the MythTV python bindings does not properly handle the transition to summer (daylight savings) time, which occurs here in the USA this coming weekend.

This is caused by scanning the transition table using the local time entry, which for the transition to DST is actually one hour ahead of the time for which the transition is being looked up.

A symptom of this issue is that attempting to convert a datetime instance from UTC to local time during the transition and the hour following will result in an incorrect result. For example:

     starttime = datetime.duck('2013-03-10T10:30:00Z')  
     print starttime.astimezone(datetime.localTZ())

will print

     2013-03-10 02:30:00-08:00

instead of

     2013-03-10 03:30:00-07:00

Attached is a testcase and a quick and dirty patch which fixes the issue. It may be more elegant to implement a fix as the zoneinfo tables are read rather than during transition search.

[Tom Grigg <tomegrigg@…>]

test case

[Tom Grigg <tomegrigg@…>]

patch

[Raymond Wagner <rwagner@…>]

In 6b01d7ba4c2a77fbeed59ba9f2671e8038432611/mythtv:

Improve time zone behavior in Python bindings at transition points.

This adds pre-computed ranges during which time zone definitions are in
effect, allowing the search to function more correctly in the hour
immediately before and after a transition.

Fixes #11447
Closes #10847