DM-47262: Add serializers for *Timedelta types

changelog.d/20241112_163814_rra_DM_47262.md

@@ -0,0 +1,7 @@
+### 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.
+
+### Bug fixes
+
+- `SecondsTimedelta` now correctly validates an input stringified floating-point number of seconds instead of truncating it to an integer.

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 +115,11 @@ 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, when_used="json"
+    ),
 ]
 """Parse a human-readable string into a `datetime.timedelta`.
 
@@ -133,7 +142,10 @@ 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)),
+    BeforeValidator(lambda v: v if not isinstance(v, str) else float(v)),
+    PlainSerializer(
+        lambda t: t.total_seconds(), return_type=float, when_used="json"
+    ),
 ]
 """Parse a float number of seconds into a `datetime.timedelta`.
 

safir/tests/pydantic_test.py

@@ -145,14 +145,20 @@ class TestModel(BaseModel):
 
     model = TestModel.model_validate({"delta": timedelta(seconds=5)})
     assert model.delta == timedelta(seconds=5)
+    assert model.model_dump(mode="python") == {"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)
+    assert model.model_dump(mode="python") == {"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)
+    model = TestModel.model_validate({"delta": "10.5"})
+    assert model.delta.total_seconds() == 10.5
 
     with pytest.raises(ValidationError):
         TestModel.model_validate({"delta": "P1DT12H"})
@@ -164,12 +170,18 @@ class TestModel(BaseModel):
 
     model = TestModel.model_validate({"delta": timedelta(seconds=5)})
     assert model.delta == timedelta(seconds=5)
+    assert model.model_dump(mode="python") == {"delta": timedelta(seconds=5)}
+    assert model.model_dump(mode="json") == {"delta": 5}
     model = TestModel.model_validate({"delta": 600})
     assert model.delta == timedelta(seconds=600)
+    assert model.model_dump(mode="python") == {"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)
+    model = TestModel.model_validate({"delta": "10.5"})
+    assert model.delta.total_seconds() == 10.5
 
     with pytest.raises(ValidationError):
         TestModel.model_validate({"delta": "P1DT12H"})