Bug report

According to ISO-8601, a time of 24:00 on a given date is a valid alternative to 00:00 of the following date, however Python does not support this, raising the following error when attempted: ValueError: hour must be in 0..23.

This bug can be seen from multiple scenarios, specifically anything that internally calls the _check_time_fields function, such as the following:

>>> import datetime
>>> datetime.datetime(2022, 1, 2, 24, 0, 0)  # should be equivalent to 2022-01-03 00:00:00
Traceback (most recent call last):
  File "<pyshell#2>", line 1, in <module>
    datetime.datetime(2022, 3, 4, 24, 0, 0)
ValueError: hour must be in 0..23

The fix for this is relatively simple: have an explicit check within _check_time_fields for the scenario where hour == 24 and minute == 0 and second == 0 and microsecond == 0, or more concisely hour == 24 and not any((minute, second, microsecond)), and in this scenario increase the day by one (adjusting the week/month/year as necessary) and set the hour to 0.

I imagine the check_time_args C function would also have to be updated.

Your environment

• CPython versions tested on: 3.9.12, 3.10.7, 3.11.2 (presumably applies to all)
• Operating system and architecture: MacOS Ventura arm64 (presumably applies to all)

Linked PRs

• gh-102450: Add ISO-8601 alternative for midnight to fromisoformat() calls. #105856