fix(python): wrap non-string global header values with str()

[patrickthornton]

Description

Fixes a mypy failure in the generated Python SDK when an API declares a non-string global header (e.g. Request-Timeout: integer, as used by Vectara).

The generator emits headers: Dict[str, str] but previously assigned the raw typed member directly, producing:

src/vectara/core/client_wrapper.py:46: error: Incompatible types in assignment
    (expression has type "int", target has type "str")  [assignment]
headers["Request-Timeout"] = self._request_timeout

No existing seed fixture declared a non-string global header, so the code path was never exercised.

Changes Made

• Added is_type_reference_string helper in client_generator/type_utilities.py that unwraps Optional/nullable/alias to detect the underlying primitive.
• Added a needs_str_conversion flag on ConstructorParameter in core_utilities/client_wrapper_generator.py, set when the header's Fern IR type is not a string.
• Updated _get_write_get_headers_body to wrap the RHS with str(...) only when needs_str_conversion is True — string-typed headers are emitted unchanged to avoid snapshot churn across existing fixtures.
• Recorded the fix in generators/python/sdk/versions.yml as 5.4.0-rc.2.

Generated code now produces:

if self._request_timeout is not None:
    headers["Request-Timeout"] = str(self._request_timeout)

• Updated README.md generator (if applicable)

Testing

Regenerated the Vectara SDK against /Users/Patrick/configs/vectara-fern-config/fern using pnpm seed run --generator python-sdk --skipScripts, then ran the generated project's CI workflow locally:

• poetry run mypy . — Success: no issues found in 906 source files

• poetry run pytest -rP -n auto . — 49 passed, 4 skipped

• poetry install --extras aiohttp && poetry run pytest -rP -n auto -m aiohttp . — 3 passed

• Unit tests added/updated

• Manual testing completed

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SDK Generation Benchmark Results

Comparing PR branch against latest nightly baseline on main (2026-04-15T21:03:37Z).

Full benchmark table (click to expand)

Generator	Spec	main (generator)	main (E2E)	PR (generator)	Delta
python-sdk	square	115s	155s	113s	-2s (-1.7%)

main (generator): generator-only time via --skip-scripts (includes Docker image build, container startup, IR parsing, and code generation — this is the same Docker-based flow customers use via fern generate). main (E2E): full customer-observable time including build/test scripts (nightly baseline, informational). Delta is computed against generator-only baseline.
⚠️ = generation exited with a non-zero exit code (timing may not reflect a successful run).
Baseline from nightly runs on main (latest: 2026-04-15T21:03:37Z). Trigger benchmark-baseline to refresh.
Last updated: 2026-04-16 02:10 UTC