Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

datetime library doesn't support valid ISO-8601 alternative for midnight #102450

Open
TizzySaurus opened this issue Mar 5, 2023 · 1 comment
Open

datetime library doesn't support valid ISO-8601 alternative for midnight #102450

TizzySaurus opened this issue Mar 5, 2023 · 1 comment
Labels
type-bug An unexpected behavior, bug, or error

Comments

@TizzySaurus
Copy link

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)
@TizzySaurus TizzySaurus added the type-bug An unexpected behavior, bug, or error label Mar 5, 2023
@terryjreedy
Copy link
Member

From the referenced wikipedia page:

As of ISO 8601-1:2019/Amd 1:2022, midnight may be referred to as "00:00:00", corresponding to the instant at the beginning of a calendar day; or "24:00:00", corresponding to the instant at the end of a calendar day.[1] ISO 8601-1:2019 as originally published removed "24:00" as a representation for the end of day although it was permitted in earlier versions of the standard.

Looking at the datetime commit log, I am pretty sure that 24:00:00 support was not removed after the 2019 version but was never there. It is obviously a nuisance.

While the doc for datetime.datetime explicitly disclaims such support ("0 <= hour < 24"), the doc for datetime.datetime.fromisoformat does not. It says "Return a datetime corresponding to a date_string in any valid ISO 8601 format, with the following exceptions:" and lists 4 exceptions. To me, the bug here is the omission of the pretty clearly intended '240000' exception. The fix would be to add the 5th exception to the doc.

The request to add support would then be a feature addition. I have no opinion, but think it less likely to be accepted than rejected.

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Assignees
No one assigned
Labels
type-bug An unexpected behavior, bug, or error
Projects
Date and time issues
Status: No status
Milestone
No milestone
Development

No branches or pull requests
2 participants
@terryjreedy @TizzySaurus