pytz brings the Olson tz database into Python. This library allows
accurate and cross platform timezone calculations using Python 2.3
or higher. It also solves the issue of ambiguous times at the end
of daylight savings, which you can read more about in the Python
Library Reference (datetime.tzinfo).

python3 is an optional dependency.  You need to set PYTHON3=yes,
for example:

  PYTHON3=yes ./pytz.SlackBuild