PY: generated modules import unused names and redefine Extension (ruff F401/F811) #258

Describe the bug

The Python generator emits modules that import names they never use, and every extension profile module that has sub-extensions imports Extension twice. mypy has no unused-import check, so the example passes CI. A pyflakes-based linter reports both: on the committed examples/python-r4-us-core/fhir_types (36 .py files), ruff reports 40 F401 and 4 F811.

Present in 0.0.21, which is also current main (5de74e1).

To Reproduce

1. Versions: @atomic-ehr/codegen 0.0.21, ruff 0.16.9, macOS. The repository has no ruff configuration.
2. No generation needed. On a checkout of 5de74e1:

ruff check --isolated --select F401,F811,F841,I examples/python-r4-us-core/fhir_types

Result: Found 78 errors.

F401 by name:

13 are in 10 profile modules. 27 are in 9 type modules under hl7_fhir_r4_core/: base.py, bundle.py, domain_resource.py, observation.py, operation_outcome.py, organization.py, patient.py, provenance.py, resource.py.

The four F811 are extension_nationality.py, extension_uscore_ethnicity_extension.py, extension_uscore_race_extension.py and extension_uscore_tribal_affiliation_extension.py. hl7_fhir_r4_core/profiles/extension_nationality.py:

from typing import Any, Literal, cast, overload

from fhir_types.hl7_fhir_r4_core.base import Extension
from fhir_types.hl7_fhir_r4_core.base import Extension
from fhir_types.hl7_fhir_r4_core.base import CodeableConcept, Period

hl7_fhir_r4_core/domain_resource.py uses none of BaseModel, PositiveInt, Literal or FhirpyBaseModel:

from __future__ import annotations
from pydantic import BaseModel, ConfigDict, Field, PositiveInt, model_validator
from typing import Any, Generic, List as PyList, Literal
from typing_extensions import Self, TypeVar
from fhir_types.fhirpy_base_model import FhirpyBaseModel

Cause, at 5de74e1:

• collectHelperImports adds helpers in groups, from structural predicates:
  • matches_value is imported for any non-type-discriminated slice (L130-L138). It is called only by the getter of a non-array slice (profile-slices.ts L216-L222).
  • The extension group, including get_extension_value, is imported for any extension (L139-L149). get_extension_value is called only by the single-value extension getter (profile-extensions.ts L349-L361).
  • Only the validate_* names come from the emitted body: generateProfileModule builds the validate() lines with collectValidateBody before it collects imports (L410-L414).
• emitModuleImports imports Any for any extension or slice (L228-L230). It imports the base type from base, then imports Extension from base again whenever the profile has extensions (L249-L254). For an extension profile the base type is Extension, which is the F811.
• generateValidateMethod writes profile_name = "..." unconditionally (L333). Every committed profile module has at least one validation call, so this is not reported today; a profile with nothing to validate gets an F841.
• Type modules: generateDefaultImports writes a fixed pydantic list (BaseModel, ConfigDict, Field, PositiveInt) and a fixed typing list (Any, List as PyList, Literal) into every base.py and resource module. generateResourceModule also calls generateFhirBaseModelImport, which imports FhirpyBaseModel into every resource module. Only a root class uses it as a base (getSuperClasses, injectSuperClasses), which in this output is resource.py.

This is not caught in CI because the Python job (sdk-tests.yml L94-L111) runs test-python-r4-us-core-example, which runs only mypy . and pytest. Nothing in the repository runs ruff, flake8 or pyflakes.

Expected result

A generated module imports each name once and imports only the names it uses, and validate() does not bind a local it does not read. ruff check --select F401,F811,F841 passes on examples/python-r4-us-core/fhir_types, and test-python-r4-us-core-example runs that check next to mypy ., the way #183 turned on strict mode for the mypy . run in the same target.

Additional context

• TS: generated profiles import unused helpers and declare unused locals (TS6133 under noUnusedLocals) #254 is the TypeScript counterpart, fixed in TS: import only the helpers and types a profile module uses #256 with collect-then-emit: build the body first, then derive the imports from what the body references. The Python profile writer already does this for the validate_* helpers; the slice and extension helpers, the typing names and the type-module imports need the same.
• The 34 I001 findings are import order only. They are left out of the proposed guard.
• ruff is not in the example's venv. python-r4-us-core-test-setup (Makefile L124-L130) installs fhir_types/requirements.txt, which is copied from assets/api/writer-generator/python/requirements.txt and lists mypy and pytest.