Unexpected results when comparing time instances

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
backend

Research direction

Reproduce the reported comparisons between timezone-aware time and datetime instances on the listed CPython versions. Trace the time and datetime comparison entry points to determine why crossing a local date changes the result, then add regression coverage showing the expected equality for equivalent absolute times.

Written by the indexing model from the issue text.

Description

extension-modules stdlib type-bug

Bug report

When comparing two time instances with different timezone, there are some unexpected result in some cases.

from datetime import datetime, time, timezone, timedelta

# Two time instances with the same absolute time in different time zones
t1 = time(hour = 0, tzinfo = timezone(timedelta(hours=1)))
t2 = time(hour = 7, tzinfo = timezone(timedelta(hours=8)))

print(t1 == t2) # True

# Another time instances with the same absolute time in different time zones, and local date is different
t3 = time(hour = 23, tzinfo = timezone(timedelta(hours=0)))
t4 = time(hour = 7, tzinfo = timezone(timedelta(hours=8)))

print(t3 == t4) # False, UNEXPECTED

# Two datetime instances with the same absolute time in different time zones and different local date
d1 = datetime(2022, 10, 10, hour = 23, tzinfo = timezone(timedelta(hours=0)))
d2 = datetime(2022, 10, 11, hour = 7, tzinfo = timezone(timedelta(hours=8)))

print(d1 == d2) # True, make sense
print(d1.timetz() == d2.timetz()) # False, UNEXPECTED

If two times with different timezones have the same absolute time, then thay should be equle. However, when the local dates of the two times are different, the comparison will be false even if the absolute time is the same.

As in the code above, the comparison between two datetimes has expected result, even though their local dates is different. However if we compare the time extracted from these two datetimes, the result will be false.

Your environment

  • CPython versions tested on: 3.9, 3.10
  • Operating system and architecture: Windows, macOS
Dominant language
Python
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