UTCDateTimeAttribute: support for pre-1000 dates (#949)

pynamodb · Jun 17, 2021 · 06bab8b · 06bab8b
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diff --git a/docs/release_notes.rst b/docs/release_notes.rst
@@ -6,6 +6,7 @@ Unreleased
 
 * Null errors should include full attribute path (#915)
 * Fix type annotation of ``is_in`` conditional expression
+* Fix for serializing and deserializing dates prior to year 1000
 
 
 v5.0.3

diff --git a/pynamodb/attributes.py b/pynamodb/attributes.py
@@ -685,7 +685,9 @@ def serialize(self, value):
         """
         if value.tzinfo is None:
             value = value.replace(tzinfo=timezone.utc)
-        fmt = value.astimezone(timezone.utc).strftime(DATETIME_FORMAT)
+        # Padding of years under 1000 is inconsistent and depends on system strftime:
+        # https://bugs.python.org/issue13305
+        fmt = value.astimezone(timezone.utc).strftime(DATETIME_FORMAT).zfill(31)
         return fmt
 
     def deserialize(self, value):
@@ -700,6 +702,8 @@ def _fast_parse_utc_date_string(date_string: str) -> datetime:
         # This is ~5.8x faster than using strptime and 38x faster than dateutil.parser.parse.
         _int = int  # Hack to prevent global lookups of int, speeds up the function ~10%
         try:
+            # Fix pre-1000 dates serialized on systems where strftime doesn't pad w/older PynamoDB versions.
+            date_string = date_string.zfill(31)
             if (len(date_string) != 31 or date_string[4] != '-' or date_string[7] != '-'
                     or date_string[10] != 'T' or date_string[13] != ':' or date_string[16] != ':'
                     or date_string[19] != '.' or date_string[26:31] != '+0000'):

diff --git a/tests/test_attributes.py b/tests/test_attributes.py
@@ -146,12 +146,19 @@ def test_utc_date_time_serialize(self):
         """
         assert self.attr.serialize(self.dt) == '2047-01-06T08:21:30.002000+0000'
 
+    def test_utc_date_time_serialize_pre_1000(self):
+        dt = self.dt.replace(year=1)
+        assert self.attr.serialize(dt) == '0001-01-06T08:21:30.002000+0000'
+
     def test_utc_date_time_deserialize(self):
         """
         UTCDateTimeAttribute.deserialize
         """
         assert self.attr.deserialize('2047-01-06T08:21:30.002000+0000') == self.dt
 
+    def test_utc_date_time_deserialize_pre_1000_not_padded(self):
+        assert self.attr.deserialize('1-01-06T08:21:30.002000+0000') == self.dt.replace(year=1)
+
     @pytest.mark.parametrize(
         "invalid_string",
         [