PY: default fieldFormat to camelCase

[ryukzak]

Default change

• Python generator now defaults fieldFormat to camelCase (was snake_case). Fields keep their FHIR spelling instead of being converted.

Generated models before/after — using FHIR field names directly avoids the snake_case ↔ alias indirection:

# before (snake_case default)
birth_date: str | None = Field(None, alias="birthDate", serialization_alias="birthDate")
marital_status: CodeableConcept[...] | None = Field(None, alias="maritalStatus", ...)

# after (camelCase default)
birthDate: str | None = Field(None, alias="birthDate", serialization_alias="birthDate")
maritalStatus: CodeableConcept[...] | None = Field(None, alias="maritalStatus", ...)

Opt back into snake_case explicitly (unchanged behavior):

.python({ fieldFormat: "snake_case" })

Generator fixes

• __pydantic_fields_set__.add(...) now uses the formatted resourceType field name instead of a hardcoded "resource_type" literal — for camelCase models the field is resourceType, so the old literal marked a non-existent field as set.

# before — wrong field name under camelCase
self.__pydantic_fields_set__.add("resource_type")
# after
self.__pydantic_fields_set__.add("resourceType")

• Dropped the TYPE_CHECKING resourceType shim from the fhirpy base model. It existed so static type-checkers saw a resourceType attribute on snake_case models (where the field is resource_type). camelCase models expose resourceType natively, so the shim is unnecessary.

Example & tests

• examples/python-r4-us-core: dropped explicit fieldFormat: "snake_case" (now uses the camelCase default) and migrated hand-written demos/tests to camelCase field access, kwargs, raw-extension dict keys, and validation-message assertions. mypy and the offline pytest suite pass.
• examples/python-r4 keeps fieldFormat: "snake_case" to retain snake_case coverage at generation level.
• Updated the python writer test assertion and regenerated affected snapshots.

Note

• snake_case + fhirpy client no longer ships the static resourceType shim, so mypy against snake_case fhirpy models will report ResourceProtocol non-conformance. The default (camelCase) is unaffected.