pytz has served the Python community well for many years, but it
is no longer the best option for providing time zones. pytz has a
non-standard interface that is very easy to misuse; this interface
was necessary when pytz was created, because datetime had no way
to represent ambiguous datetimes, but this was solved in in Python
3.6, which added a fold attribute to datetimes in PEP 495. With
the addition of the zoneinfo module in Python 3.9 (PEP 615), there
has never been a better time to migrate away from pytz.

However, since pytz time zones are used very differently from a
standard tzinfo, and many libraries have built pytz zones into
their standard time zone interface (and thus may have users relying
on the existence of the localize and normalize methods); this
library provides shim classes that are compatible with both PEP
495 and pytz's interface, to make it easier for libraries to
deprecate pytz.