ASCReader: Improve datetime parsing and support double-defined AM/PM cases

[Gedlex]

Summary of Changes

The datetime handling has been improved to robustly handle double-defined datetime strings where both a 24h timestamp and an AM/PM suffix are present (e.g. "30 15:06:13.191 pm 2017") which previously caused parsing to fail.

Key improvements:

• Added support for “double-defined” datetime strings
• Cleaned up month replacement logic using a safer KeyError-handling path
• Added clearer error messages for unknown months and incompatible formats

A small unit test was used during development:

from can.io.asc import ASCReader

# Define test strings
test_strings = ["May 27 04:09:35.000 pm 2014",
                "Mai 27 04:09:35.000 pm 2014",
                "Apr 28 10:44:52.480 2022",
                "Apr 28 10:44:52.480 am 2022",
                "Sep 30 15:06:13.191 2017",
                "Sep 30 15:06:13.191 pm 2017", # double defined case
                "Sep 30 15:06:13.191 am 2017", # technically invalid case
                ]

# Test function
for string in test_strings:
    res = ASCReader._datetime_to_timestamp(string)
    print(f"Timestamp for {string} is {res}")

Type of Change

• Bug fix
• New feature
• Documentation update
• Refactoring
• Other (please describe):

Checklist

• I have followed the contribution guide.
• I have added or updated tests as appropriate.
• I have added or updated documentation as appropriate.
• I have added a news fragment for towncrier.
• All checks and tests pass (tox).

[zariiii9003]

Please use black to fix the code formatting and add a news fragment.

Also, here's a test you could add to test/logformats_test.py::TestAscFileFormat

    @parameterized.expand(
        [
            ("May 27 04:09:35.000 pm 2014", 1401199775.0),
            ("Mai 27 04:09:35.000 pm 2014", 1401199775.0),
            ("Apr 28 10:44:52.480 2022", 1651135492.48),
            ("Sep 30 15:06:13.191 2017", 1506776773.191),
            ("Sep 30 15:06:13.191 pm 2017", 1506776773.191),
            ("Sep 30 15:06:13.191 am 2017", 1506776773.191),
        ]
    )
    def test_datetime_to_timestamp(self, datetime_string: str, expected_timestamp: float):
        timestamp = can.ASCReader._datetime_to_timestamp(datetime_string)
        self.assertAlmostEqual(timestamp, expected_timestamp)

[Gedlex]

Thank you for the detailed feedback. I updated the formatting as requested and added your test case to test/logformats_test.py::TestAscFileFormat.

[zariiii9003]

Thank you 👍