I would prefer exposing tm_gmtoff in time.localtime() output. The advantage is that on platforms that support it is struct tm, it will return correct offset for times in the past, not only for the current time. See issue1647654.

On platforms without tm_gmtoff we can fill it with -tm_isdst?timezone:altzone.  The current situation on Linux is just backwards: we are trying to divine altzone by sampling tm_gmtoff and throw tm_gmtoff away.

See http://blogs.gnome.org/jamesh/2006/12/31/python-timetimezone-timealtzone-edge-case/.