tzset

tzset()

Initialize, or reinitialize, the local timezone to the value stored in
os.environ['TZ']. The TZ environment variable should be specified in
standard Unix timezone format as documented in the tzset man page
(eg. 'US/Eastern', 'Europe/Amsterdam'). Unknown timezones will silently
fall back to UTC. If the TZ environment variable is not set, the local
timezone is set to the systems best guess of wallclock time.
Changing the TZ environment variable without calling tzset *may* change
the local timezone used by methods such as localtime, but this behaviour
should not be relied on.