Audit and update usage of pytz to normalize and localize dates

[dirkcuys]

zoneinfo default timezone implementation

The Python standard library’s zoneinfo is now the default timezone implementation in Django.

This is the next step in the migration from using pytz to using zoneinfo. Django 3.2 allowed the use of non-pytz time zones. Django 4.0 makes zoneinfo the default implementation. Support for pytz is now deprecated and will be removed in Django 5.0.

zoneinfo is part of the Python standard library from Python 3.9. The backports.zoneinfo package is automatically installed alongside Django if you are using Python 3.8.

The move to zoneinfo should be largely transparent. Selection of the current timezone, conversion of datetime instances to the current timezone in forms and templates, as well as operations on aware datetimes in UTC are unaffected.

However, if you are working with non-UTC time zones, and using the pytz normalize() and localize() APIs, possibly with the TIME_ZONE setting, you will need to audit your code, since pytz and zoneinfo are not entirely equivalent.

To give time for such an audit, the transitional USE_DEPRECATED_PYTZ setting allows continued use of pytz during the 4.x release cycle. This setting will be removed in Django 5.0.

In addition, a pytz_deprecation_shim package, created by the zoneinfo author, can be used to assist with the migration from pytz. This package provides shims to help you safely remove pytz, and has a detailed migration guide showing how to move to the new zoneinfo APIs.

Using pytz_deprecation_shim and the USE_DEPRECATED_PYTZ transitional setting is recommended if you need a gradual update path.