fix (de-)serialization of pendulum durations

Author: hoesler

pydantic_extra_types/pendulum_dt.py

@@ -186,7 +186,65 @@ def __get_pydantic_core_schema__(cls, source: type[Any], handler: GetCoreSchemaH
         Returns:
             A Pydantic CoreSchema with the Duration validation.
         """
-        return core_schema.no_info_wrap_validator_function(cls._validate, core_schema.timedelta_schema())
+        return core_schema.no_info_wrap_validator_function(
+            cls._validate,
+            core_schema.timedelta_schema(),
+            serialization=core_schema.plain_serializer_function_ser_schema(
+                lambda instance: instance.to_iso8601_string()
+            ),
+        )
+
+    def to_iso8601_string(self) -> str:
+        """
+        Convert a Duration object to an ISO 8601 string.
+
+        In addition to the standard ISO 8601 format, this method also supports the representation of fractions of a second and negative durations.
+
+        Args:
+            duration (Duration): The Duration object.
+
+        Returns:
+            str: The ISO 8601 string representation of the duration.
+        """
+        # Extracting components from the Duration object
+        years = self.years
+        months = self.months
+        days = self._days
+        hours = self.hours
+        minutes = self.minutes
+        seconds = self.remaining_seconds
+        milliseconds = self.microseconds // 1000
+        microseconds = self.microseconds % 1000
+
+        # Constructing the ISO 8601 duration string
+        iso_duration = 'P'
+        if years or months or days:
+            if years:
+                iso_duration += f'{years}Y'
+            if months:
+                iso_duration += f'{months}M'
+            if days:
+                iso_duration += f'{days}D'
+
+        if hours or minutes or seconds or milliseconds or microseconds:
+            iso_duration += 'T'
+            if hours:
+                iso_duration += f'{hours}H'
+            if minutes:
+                iso_duration += f'{minutes}M'
+            if seconds or milliseconds or microseconds:
+                iso_duration += f'{seconds}'
+                if milliseconds or microseconds:
+                    iso_duration += f'.{milliseconds:03d}'
+                if microseconds:
+                    iso_duration += f'{microseconds:03d}'
+                iso_duration += 'S'
+
+        # Prefix with '-' if the duration is negative
+        if self.total_seconds() < 0:
+            iso_duration = '-' + iso_duration
+
+        return iso_duration
 
     @classmethod
     def _validate(cls, value: Any, handler: core_schema.ValidatorFunctionWrapHandler) -> Duration:
@@ -219,10 +277,27 @@ def _validate(cls, value: Any, handler: core_schema.ValidatorFunctionWrapHandler
                 microseconds=value.microseconds,
             )
 
+        assert isinstance(value, str)
         try:
-            parsed = parse(value, exact=True)
-            if not isinstance(parsed, timedelta):
+            # https://github.com/python-pendulum/pendulum/issues/532
+            if value.startswith('-'):
+                parsed = parse(value.lstrip('-'), exact=True)
+            else:
+                parsed = parse(value, exact=True)
+            if not isinstance(parsed, _Duration):
                 raise ValueError(f'value is not a valid duration it is a {type(parsed)}')
-            return Duration(seconds=parsed.total_seconds())
+            if value.startswith('-'):
+                parsed = -parsed
+
+            return Duration(
+                years=parsed.years,
+                months=parsed.months,
+                weeks=parsed.weeks,
+                days=parsed.remaining_days,
+                hours=parsed.hours,
+                minutes=parsed.minutes,
+                seconds=parsed.remaining_seconds,
+                microseconds=parsed.microseconds,
+            )
         except Exception as exc:
             raise PydanticCustomError('value_error', 'value is not a valid duration') from exc

tests/test_pendulum_dt.py

@@ -283,6 +283,31 @@ def test_pendulum_duration_from_serialized(delta_t_str):
     assert isinstance(model.delta_t, pendulum.Duration)
 
 
+@pytest.mark.parametrize(
+    'duration',
+    [
+        (Duration(months=1)),
+        (Duration(weeks=1)),
+        (Duration(milliseconds=1)),
+        (Duration(microseconds=1)),
+        (Duration(days=1)),
+        (Duration(hours=1)),
+        (Duration(minutes=1)),
+        (Duration(seconds=1)),
+        (Duration(months=2, days=5)),
+        (Duration(weeks=3, hours=12)),
+        (Duration(days=10, minutes=30)),
+        (Duration(weeks=1, days=2, hours=3)),
+        (Duration(seconds=30, milliseconds=500)),
+    ],
+)
+def test_pendulum_duration_serialization_roundtrip(duration):
+    adapter = TypeAdapter(Duration)
+    serialized = adapter.dump_python(duration)
+    deserialized = TypeAdapter.validate_python(adapter, serialized)
+    assert deserialized == duration
+
+
 def get_invalid_dt_common():
     return [
         None,