Repository navigation
[Bug]: durable_execution(plugins=...) return type fails mypy with "Too few arguments" #921
Description
Expected Behavior
@durable_execution(plugins=[...]) applied to a def handler(event, context) passes mypy.
Actual Behavior
mypy 2.4.1 reports error: Too few arguments [call-arg] on the @durable_execution( line. Three call sites on main show it:
packages/aws-durable-execution-sdk-python-conformance-tests-telemetry/src/telemetry_1_success.py:42packages/aws-durable-execution-sdk-python-conformance-tests-telemetry/src/telemetry_3_result_select.py:66packages/aws-durable-execution-sdk-python-conformance-tests-otel/src/otel_5_child_context.py:30
Cause. durable_execution has one signature: execution.py:169-174. Its declared return type is Callable[[Any, LambdaContext], Any] for both call forms. When func is None, the function returns a decorator at runtime (execution.py:187-191). The declared type is still the two-argument handler. The decorator syntax then applies that two-argument type to the user function with one argument. So mypy reports Too few arguments.
CI does not catch it. .github/scripts/type-checks.sh runs mypy on five packages. It excludes the three conformance-test packages, which hold every plugins= call site.
Steps to Reproduce
mypy packages/aws-durable-execution-sdk-python-conformance-tests-telemetry/src/telemetry_3_result_select.py
SDK Version
main at 93751c46
Python Version
3.14
Is this a regression?
No
Last Working Version
No response
Additional Context
Proposed fix: two @overloads on durable_execution.
funcgiven positionally → returnsCallable[[Any, LambdaContext], Any].func: None = Nonewith keyword-onlyboto3_clientandplugins→ returnsCallable[[Callable[[Any, DurableContext], Any]], Callable[[Any, LambdaContext], Any]].
Add a test under packages/aws-durable-execution-sdk-python/tests that uses both call forms, so types:check covers the decorator-factory form.
Raised by @ParidelPooya in the #916 review.
Activity
pcbeingused333 commentedon Nov 11, 2026
Design note for CONTRIBUTING rule 3: the parameterized decorator form should pass mypy while preserving the existing bare-decorator form.
The cause described above is still present on main (
e436a33f): the factory call is annotated as a two-argument handler even though it returns a decorator.The options are to simplify the existing implementation, use a union return type, or describe the two call forms with overloads; the runtime already has the required two paths, and a union would leave both forms ambiguous to the type checker, so I propose the two overloads outlined in the issue, with no runtime changes and nothing removed.
Validation would add a failing type-check case for
@durable_execution(plugins=[])alongside the bare@durable_executionform under the core package'stests/, which is already covered bytypes:check, and run the core unit tests without modifying any conformance-test package.If a maintainer agrees with this design, I can prepare the PR.