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Pendulum interval seems incompatible with Python native datetime #906
Description
- I am on the latest Pendulum version.
- I have searched the issues of this repo and believe that this is not a duplicate.
- OS version and name: macOS 15.5 (24F74)
- Python version: 3.12.10
- Pendulum version: 3.1.0
Issue
I'm new to pendulum and am sorry if this issue is a duplicate.
Set up
The documentation advertises compatibility with native Python datetime.datetime:
>>> from datetime import datetime
>>> import pendulum
>>> dt = pendulum.datetime(2015, 2, 5)
>>> isinstance(dt, datetime)
TrueSo I thought I could do this:
start_time = datetime(2025, 7, 25, 19, 26, 34)
end_time = datetime(2025, 7, 29, 19, 26, 34)
interval = pendulum.interval(start_time, end_time)Unexpected behaviour
It turns out I can't:
>>> interval.in_words()
'3 days 4 hours 33 minutes'
>>> interval.days
4
>>> interval.hours
4
>>> interval.minutes
33
>>> interval.in_days()
4
>>> interval.in_hours() / 24
4.0I now understand that I should've started with:
start_time = pendulum.datetime(2025, 7, 25, 19, 26, 34)
end_time = pendulum.datetime(2025, 7, 29, 19, 26, 34)or
start_time = pendulum.instance(start_time)
end_time = pendulum.instance(end_time)But still, the above behaviour is extremely confusing, unless I'm missing something of course.
Expected behaviour
I personally would expect pendulum to either (in the order of preference):
- Treat Python's native
datetime.datetimethe same way aspendulum.datetime. - Fail at
interval()instantiation with aTypeErrororValueError. - Document clearly that native
datetime.datetimeis not fully supported.
Activity
[-]Pendulum intervals seems incompatible with Python native `datetime`[/-][+]Pendulum 'interval' seems incompatible with Python native `datetime`[/+][-]Pendulum 'interval' seems incompatible with Python native `datetime`[/-][+]Pendulum `interval` seems incompatible with Python native `datetime`[/+]ashb commentedon Aug 2, 2025
This appears to be some bug specifically with the
in_words()function -- all the rest of the things such astotal_secondswork correctly and report 345600.0 ( == 86400 * 4 = 24 * 60 * 60 * 4)Eren-Acar commentedon Oct 24, 2025
When I looked at it in more detail I realized that inconsistency in the
in_words()function exists in only version 3.1. When I tested it again in development version (3.2.0.dev0), I saw that both Native DateTime and Pendulum DateTime gave correct and same results, but I couldn't figure out after which commit this issue was resolved.@ashb @ayorgo To sum up, could you try again in
3.2.0.dev0? I think this bug has already been fixed in the development version.fix: precise_diff inconsistent with pendulum.DateTime subclasses