Summary

Fixes a bug where invalid/unknown locales would default to month-first (American) format instead of day-first format. Since most of the world uses day-first, this is the better default.

Problem

When an invalid or unknown locale was provided (e.g., typo, unsupported locale), the exception handler would return False (month-first):

except Exception:
    return False  # ❌ Defaults to month-first (MM/DD/YYYY)

This caused incorrect parsing:

• User provides locale="xyz_ABC" (typo)
• Date "01/02/2023" gets parsed as January 2nd (month-first)
• Should be parsed as February 1st (day-first, more common globally)

Why this is wrong

Only a handful of locales use month-first format:

• en_US - American English
• A few Pacific island locales

Most of the world uses day-first:

• All of Europe
• Most of Asia
• Middle East
• Africa
• South America
• Australia

Solution

Changed exception handler to return True (day-first) for invalid locales:

except Exception:
    # Invalid/unknown locale: default to day-first since most of the world uses it
    # Only en_US and a few other locales use month-first (MM/DD/YYYY)
    return True  # ✅ Defaults to day-first (DD/MM/YYYY)

The logic now:

1. ISO 8601 (YYYY-MM-DD) → False (month before day)
2. No locale (None) → False (backward compat, American default)
3. Valid locale → Check Babel CLDR data
4. Invalid locale → True (day-first is global default)

Code Changes

Before:

except Exception:
    return False  # Defaulted to month-first

After:

except Exception:
    # Invalid/unknown locale: default to day-first since most of the world uses it
    # Only en_US and a few other locales use month-first (MM/DD/YYYY)
    return True  # Default to day-first (DD/MM/YYYY)

Testing

Updated test:

def test_invalid_locale_returns_true(self) -> None:
    # Invalid/unknown locales default to day-first since most of world uses it
    assert _should_use_day_first("01/15/2023", "invalid_LOCALE") is True
    assert _should_use_day_first("15/01/2023", "xyz_ABC") is True

New integration test:

def test_invalid_locale_defaults_to_day_first(self) -> None:
    parser = TimestampParser()
    
    # With an invalid locale, ambiguous dates should parse as day-first
    with set_locale_context("invalid_LOCALE"):
        result = parser.parse("01/02/2023")
    assert "2023-02-01" in result  # February 1st (day-first)

• ✅ All 19 timestamp parser tests pass
• ✅ All 547 tests pass
• ✅ Linting clean

Impact

• Fixes bug - Invalid locales now use the globally more common format
• Better user experience - Fewer parsing errors for international users
• No breaking changes - Only affects invalid locale case (which was already broken)
• Backward compatible - None locale still defaults to American format

🤖 Generated with Claude Code