CI: enable python3.15 job

[Alvaro-Kothe]

• closes BUG: A test_to_datetime.py test fails on Python 3.15 #66436 (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.
• I have reviewed and followed all the contribution guidelines
• If I used AI to develop this pull request, I prompted it to follow AGENTS.md.

[Alvaro-Kothe]

This follows python/cpython#132922. It changed the behavior to make the %z format optional.

$ cmd='import datetime; print(datetime.datetime.strptime("2010-01-01 12:00:00", "%Y-%m-%d %H:%M:%S%z"))'

$ /usr/bin/python3.14 -c "$cmd"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
    import datetime; print(datetime.datetime.strptime("2010-01-01 12:00:00", "%Y-%m-%d %H:%M:%S%z"))
                           ~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.14/_strptime.py", line 815, in _strptime_datetime_datetime
    tt, fraction, gmtoff_fraction = _strptime(data_string, format)
                                    ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.14/_strptime.py", line 555, in _strptime
    raise ValueError("time data %r does not match format %r" %
                     (data_string, format))
ValueError: time data '2010-01-01 12:00:00' does not match format '%Y-%m-%d %H:%M:%S%z'

$ ~/opt/python315-asan/bin/python3.15 -c "$cmd"
2010-01-01 12:00:00

Is this change correct, or we should be raising an error in case group_val is None?

cc @jbrockmendel

[jbrockmendel]

My instinct is that we should not be following the stdlib on this because it can lead to weird behavior in mixed-input cases. But I need to look into the consequences more closely before giving a strong opinion.

[jbrockmendel]

I think we should do something like

if group_val is None:
    raise ValueError(f"time data \"{val}\" doesn't match format \"{fmt}\"")
tz = parse_timezone_directive(group_val)

[jbrockmendel]

then we keep the existing behavior

[Alvaro-Kothe]

done

[jbrockmendel]

can we condition this on PY315 so that we can eventually simplify it

[Alvaro-Kothe]

Check if it's better now. The only place where I didn't apply the conditional was in test_constructor_keyword, but added a comment to compensate.

[jbrockmendel]

23 corresponds to "N" in _parse_code_table. I think several of these are off

[Alvaro-Kothe]

Removed the elif above it, since it's not present in CPython's code. Thanks for pointing it out.

[jbrockmendel]

Does to_datetime(["2010-01-01 12:00:00+04:00"], format="%Y-%m-%d %H:%M:%S%:z") correctly raise ValueError? I think it might be an incorrect KeyError here

[Alvaro-Kothe]

Does to_datetime(["2010-01-01 12:00:00+04:00"], format="%Y-%m-%d %H:%M:%S%:z") correctly raise ValueError? I think it might be an incorrect KeyError here

It was raising KeyError because colon_z was not in the dictionary. I ported python/cpython#136961 to handle %:z and added tests for it. If the intended behavior is to raise an error, we probably can check if colon_z was parsed and raise an error.