Inconsistent behavior of fromisoformat methods in datetime module implementations

[donBarbos]

Bug report

Bug description:

1. Incorrect timezone validation in _pydatetime (solved)

As far as I understand, the documentation says that Z char should mean that tzinfo is timezone.utc, so there cannot be any time zone fields after it.
Based on this, _pydatetime implementation is incorrect, right?

>>> import _datetime, _pydatetime
>>> _pydatetime.datetime.fromisoformat('2020-01-01T00:00Z00:50')
datetime.datetime(2020, 1, 1, 0, 0, tzinfo=datetime.timezone(datetime.timedelta(seconds=3000)))
>>> _datetime.datetime.fromisoformat('2020-01-01T00:00Z00:50')
Traceback (most recent call last):
  File "<python-input-54>", line 1, in <module>
    _datetime.datetime.fromisoformat('2020-01-01T00:00Z00:50')
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^
ValueError: Invalid isoformat string: '2020-01-01T00:00Z00:50'

2. Miss the wrong millisecond separator in _datetime (solved)

In _pydatetime the separator for milliseconds must be either a period . or a comma ,.
Should we allow colon : as millisecond separator?

>>> import _datetime, _pydatetime
>>> _datetime.datetime.fromisoformat('2020-01-01T00:00:01:1')
datetime.datetime(2020, 1, 1, 0, 0, 1, 100000)
>>> _pydatetime.datetime.fromisoformat('2020-01-01T00:00:01:1')
Traceback (most recent call last):
  File "<python-input-119>", line 1, in <module>
    _pydatetime.datetime.fromisoformat('2020-01-01T00:00:01:1')
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../cpython/Lib/_pydatetime.py", line 1969, in fromisoformat
    "Return local time tuple compatible with time.localtime()."
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    dst = self.dst()
    ^^^^^^^^^^^^^^^^
ValueError: Invalid isoformat string: '2020-01-01T00:00:01:1'

3. The first errors caught can be different

If these errors occur separately, then both implementations are able to detect them, but when there are several problems, the methods may behave differently. In this case _pydatetime first detected an error due to the separator, and _datetime first detected an error in exceeding the limits.

>>> import _datetime, _pydatetime
>>> _pydatetime.datetime.fromisoformat('2009-04-19T03:15:45+10:90.11')
Traceback (most recent call last):
  File "<python-input-40>", line 1, in <module>
    _pydatetime.datetime.fromisoformat('2009-04-19T03:15:45+10:90.11')
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../cpython/Lib/_pydatetime.py", line 1969, in fromisoformat
            f'Invalid isoformat string: {date_string!r}') from None
    else:
ValueError: Invalid isoformat string: '2009-04-19T03:15:45+10:90.11'
>>> _datetime.datetime.fromisoformat('2009-04-19T03:15:45+10:90.11')
Traceback (most recent call last):
  File "<python-input-41>", line 1, in <module>
    _datetime.datetime.fromisoformat('2009-04-19T03:15:45+10:90.11')
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ValueError: minute must be in 0..59

---

Also also an issue has already been created about the fact that some errors have different output, here:

• datetime error message is different between _pydatetime.py and _datetimemodule.c #109798

I'll send a PR.

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-127260: Make more consistent to raising errors of fromisoformat methods in both implementations #130134

[picnixz]

Ah crap I thought this one was a PR. Reverting the title.