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Decorators

step #

step(func: Callable[P, R]) -> StepFunction[P, R]

step(*, workflow: type['Workflow'] | None = None, num_workers: int = 4, retry_policy: RetryPolicy | None = None, skip_graph_checks: list[StepGraphCheck] | None = None) -> Callable[[Callable[P, R]], StepFunction[P, R]]

step(func: Callable[P, R] | None = None, *, workflow: type['Workflow'] | None = None, num_workers: int = 4, retry_policy: RetryPolicy | None = None, skip_graph_checks: list[StepGraphCheck] | None = None) -> Callable[[Callable[P, R]], StepFunction[P, R]] | StepFunction[P, R]

Decorate a callable to declare it as a workflow step.

The decorator inspects the function signature to infer the accepted event type, return event types, optional Context parameter (optionally with a typed state model), and any resource injections via typing.Annotated.

When applied to free functions, provide the workflow class via workflow=MyWorkflow. For instance methods, the association is automatic.

Parameters:

Name Type Description Default
workflow type[Workflow] | None

Workflow class to attach the free function step to. Not required for methods.

 None
num_workers int

Number of workers for this step. Defaults to 4.

 4
retry_policy RetryPolicy | None

Optional retry policy for failures.

 None
skip_graph_checks list[str] | None

Graph validation checks to skip for this step. Currently supports "reachability" to allow intentionally unreachable steps.

 None

Returns:

Name Type Description
Callable Callable[[Callable[P, R]], StepFunction[P, R]] | StepFunction[P, R]

The original function, annotated with internal step metadata.

Raises:

Type Description
WorkflowValidationError

If signature validation fails or when decorating a free function without specifying workflow.

Examples:

Method step:

class MyFlow(Workflow):
    @step
    async def start(self, ev: StartEvent) -> StopEvent:
        return StopEvent(result="done")

Free function step:

class MyWorkflow(Workflow):
    pass

@step(workflow=MyWorkflow)
async def generate(ev: StartEvent) -> NextEvent: ...
Source code in workflows/decorators.py 
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def step(
    func: Callable[P, R] | None = None,
    *,
    workflow: type["Workflow"] | None = None,
    num_workers: int = 4,
    retry_policy: RetryPolicy | None = None,
    skip_graph_checks: list[StepGraphCheck] | None = None,
) -> Callable[[Callable[P, R]], StepFunction[P, R]] | StepFunction[P, R]:
    """
    Decorate a callable to declare it as a workflow step.

    The decorator inspects the function signature to infer the accepted event
    type, return event types, optional `Context` parameter (optionally with a
    typed state model), and any resource injections via `typing.Annotated`.

    When applied to free functions, provide the workflow class via
    `workflow=MyWorkflow`. For instance methods, the association is automatic.

    Args:
        workflow (type[Workflow] | None): Workflow class to attach the free
            function step to. Not required for methods.
        num_workers (int): Number of workers for this step. Defaults to 4.
        retry_policy (RetryPolicy | None): Optional retry policy for failures.
        skip_graph_checks (list[str] | None): Graph validation checks to skip
            for this step. Currently supports ``"reachability"`` to allow
            intentionally unreachable steps.

    Returns:
        Callable: The original function, annotated with internal step metadata.

    Raises:
        WorkflowValidationError: If signature validation fails or when decorating
            a free function without specifying `workflow`.

    Examples:
        Method step:

        ```python
        class MyFlow(Workflow):
            @step
            async def start(self, ev: StartEvent) -> StopEvent:
                return StopEvent(result="done")
        ```

        Free function step:

        ```python
        class MyWorkflow(Workflow):
            pass

        @step(workflow=MyWorkflow)
        async def generate(ev: StartEvent) -> NextEvent: ...
        ```
    """

    def decorator(func: Callable[P, R]) -> StepFunction[P, R]:
        localns = _capture_decorator_localns()
        return _apply_step_decorator(
            func,
            num_workers=num_workers,
            retry_policy=retry_policy,
            workflow=workflow,
            localns=localns,
            skip_graph_checks=skip_graph_checks or [],
        )

    if func is not None:
        # The decorator was used without parentheses, like `@step`
        localns = _capture_callsite_localns()
        return _apply_step_decorator(
            func,
            num_workers=num_workers,
            retry_policy=retry_policy,
            workflow=workflow,
            localns=localns,
            skip_graph_checks=skip_graph_checks or [],
        )
    return decorator