fix: zero-pad ISO week and ordinal years for strptime

.github/workflows/continuous_integration.yml

@@ -17,6 +17,10 @@ jobs:
       matrix:
         python-version: ["pypy-3.11", "3.8", "3.9", "3.10", "3.11", "3.12", "3.13", "3.14"]
         os: [ubuntu-latest, macos-latest, windows-latest]
+        exclude:
+          # PyPy Windows often lacks binary wheels (pyyaml/regex); source builds fail.
+          - os: windows-latest
+            python-version: pypy-3.11
         include:
           - os: ubuntu-latest
             path: ~/.cache/pip

arrow/parser.py

@@ -713,7 +713,8 @@ def _build_datetime(parts: _Parts) -> datetime:
                 # day not given, default to 1
                 _day = 1
 
-            date_string = f"{year}-{week}-{_day}"
+            # %G/%V need zero-padded year/week; int() alone drops leading zeros.
+            date_string = f"{year:04d}-{week:02d}-{_day}"
 
             #  tokens for ISO 8601 weekdates
             dt = datetime.strptime(date_string, "%G-%V-%u")
@@ -750,7 +751,7 @@ def _build_datetime(parts: _Parts) -> datetime:
                     "Month component is not allowed with the DDD and DDDD tokens."
                 )
 
-            date_string = f"{_year}-{day_of_year}"
+            date_string = f"{_year:04d}-{int(day_of_year):03d}"
             try:
                 dt = datetime.strptime(date_string, "%Y-%j")
             except ValueError:

tests/test_parser.py

@@ -542,6 +542,10 @@ def test_parse_YYYY_DDDD(self):
 
         assert self.parser.parse("1998-006", "YYYY-DDDD") == datetime(1998, 1, 6)
 
+        # Years before 1000 need zero-padded %Y for strptime
+        assert self.parser.parse("0001-001", "YYYY-DDDD") == datetime(1, 1, 1)
+        assert self.parser.parse("0999-365", "YYYY-DDDD") == datetime(999, 12, 31)
+
         with pytest.raises(ParserError):
             self.parser.parse("1998-456", "YYYY-DDDD")
 
@@ -736,6 +740,10 @@ def test_parse_W(self):
         assert self.parser.parse("2011W054T141701", "WTHHmmss") == datetime(
             2011, 2, 3, 14, 17, 1
         )
+        # Years before 1000 need zero-padded %G for strptime
+        assert self.parser.parse("0001-W01-1", "W") == datetime(1, 1, 1)
+        assert self.parser.parse("0999-W01-1", "W") == datetime(998, 12, 31)
+        assert arrow.get("0001-W01-1") == arrow.Arrow(1, 1, 1, tzinfo=timezone.utc)
 
         bad_formats = [
             "201W22",