Add serializers for *Timedelta types

Add serializers to `HumanTimedelta` and `SecondsTimedelta` that
serialize those Pydantic fields to a float number of seconds instead
of ISO 8601 durations. This means those data types now can be
round-tripped (serialized and then deserialized to the original
value), whereas before they could not be. This also avoids ISO 8601
durations in service replies that use models including those types.

changelog.d/20241112_163814_rra_DM_47262.md

@@ -0,0 +1,3 @@
+### Backwards-incompatible changes
+
+- Add serializers to `HumanTimedelta` and `SecondsTimedelta` that serialize those Pydantic fields to a float number of seconds instead of ISO 8601 durations. This means those data types now can be round-tripped (serialized and then deserialized to the original value), whereas before they could not be.

safir/src/safir/pydantic/_types.py

@@ -6,7 +6,12 @@
 from datetime import timedelta
 from typing import Annotated, TypeAlias
 
-from pydantic import AfterValidator, BeforeValidator, UrlConstraints
+from pydantic import (
+    AfterValidator,
+    BeforeValidator,
+    PlainSerializer,
+    UrlConstraints,
+)
 from pydantic_core import Url
 
 from safir.datetime import parse_timedelta
@@ -110,7 +115,9 @@ def _validate_human_timedelta(v: str | float | timedelta) -> float | timedelta:
 
 
 HumanTimedelta: TypeAlias = Annotated[
-    timedelta, BeforeValidator(_validate_human_timedelta)
+    timedelta,
+    BeforeValidator(_validate_human_timedelta),
+    PlainSerializer(lambda t: t.total_seconds(), return_type=float),
 ]
 """Parse a human-readable string into a `datetime.timedelta`.
 
@@ -134,6 +141,7 @@ def _validate_human_timedelta(v: str | float | timedelta) -> float | timedelta:
 SecondsTimedelta: TypeAlias = Annotated[
     timedelta,
     BeforeValidator(lambda v: v if not isinstance(v, str) else int(v)),
+    PlainSerializer(lambda t: t.total_seconds(), return_type=float),
 ]
 """Parse a float number of seconds into a `datetime.timedelta`.
 

safir/tests/pydantic_test.py

@@ -145,12 +145,14 @@ class TestModel(BaseModel):
 
     model = TestModel.model_validate({"delta": timedelta(seconds=5)})
     assert model.delta == timedelta(seconds=5)
+    assert model.model_dump(mode="json") == {"delta": 5}
     model = TestModel.model_validate({"delta": "4h5m18s"})
     assert model.delta == timedelta(hours=4, minutes=5, seconds=18)
     model = TestModel.model_validate({"delta": 600})
     assert model.delta == timedelta(seconds=600)
     model = TestModel.model_validate({"delta": 4.5})
     assert model.delta.total_seconds() == 4.5
+    assert model.model_dump(mode="json") == {"delta": 4.5}
     model = TestModel.model_validate({"delta": "300"})
     assert model.delta == timedelta(seconds=300)
 
@@ -164,10 +166,12 @@ class TestModel(BaseModel):
 
     model = TestModel.model_validate({"delta": timedelta(seconds=5)})
     assert model.delta == timedelta(seconds=5)
+    assert model.model_dump(mode="json") == {"delta": 5}
     model = TestModel.model_validate({"delta": 600})
     assert model.delta == timedelta(seconds=600)
     model = TestModel.model_validate({"delta": 4.5})
     assert model.delta.total_seconds() == 4.5
+    assert model.model_dump(mode="json") == {"delta": 4.5}
     model = TestModel.model_validate({"delta": "300"})
     assert model.delta == timedelta(seconds=300)