[Python] Is it possible to type hint a callable that takes positional arguments only using a...

In python, is it possible to type hint a callable that takes positional arguments only using a generic for the positional type?

The context is that I want a to ingest positional args only. See this temporalio code:

@overload
async def execute_activity(
activity: Callable[..., Awaitable[ReturnType]],
arg: None,
*,
args: Sequence[Any],
task_queue: Optional[str] = None,
schedule_to_close_timeout: Optional[timedelta] = None,
schedule_to_start_timeout: Optional[timedelta] = None,
start_to_close_timeout: Optional[timedelta] = None,
heartbeat_timeout: Optional[timedelta] = None,
retry_policy: Optional[temporalio.common.RetryPolicy] = None,
cancellation_type: ActivityCancellationType = ActivityCancellationType.TRY_CANCEL,
activity_id: Optional[str] = None,
versioning_intent: Optional[VersioningIntent] = None,
) -> ReturnType: ...


https://docs.temporal.io/develop/python/core-application#activity-execution

activity is a callable where Any positional args are allowed. I want a generic for the ... input, so I can use it to pass in the typed arg input in the args input.

It looks like I could use ParamSpec but that allows keyword args too, and appears that it would not throw needed errors when keyword args are defined. Is there a way to do this in python where the input positional arg type in activity can be used as the args type in that signature? How can I do this?

My goal would be some psudocode like:

@overload
async def execute_activity(
activity: Callable[GenericIterable, Awaitable[ReturnType]],
arg: None,
*,
args: GenericIterable,
task_queue: Optional[str] = None,
schedule_to_close_timeout: Optional[timedelta] = None,
schedule_to_start_timeout: Optional[timedelta] = None,
start_to_close_timeout: Optional[timedelta] = None,
heartbeat_timeout: Optional[timedelta] = None,
retry_policy: Optional[temporalio.common.RetryPolicy] = None,
cancellation_type: ActivityCancellationType = ActivityCancellationType.TRY_CANCEL,
activity_id: Optional[str] = None,
versioning_intent: Optional[VersioningIntent] = None,
) -> ReturnType: ...

# where the below function could be input

def some_activity(a: int, b: str) -> float:
# sample allowed activity definition
return 3.14


The solution may be: don't do that, use one input and output type so that generics/type hints will do their job here.

Working answer is below


If you want this in temporal upvote this feature request: https://github.com/temporalio/sdk-python/issues/779

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