Skip to content

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) -> 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) -> 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

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 
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
def step(
    func: Callable[P, R] | None = None,
    *,
    workflow: Type["Workflow"] | None = None,
    num_workers: int = 4,
    retry_policy: RetryPolicy | 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.

    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]:
        if not isinstance(num_workers, int) or num_workers <= 0:
            raise WorkflowValidationError(
                "num_workers must be an integer greater than 0"
            )

        func = make_step_function(func, num_workers, retry_policy)

        # If this is a free function, call add_step() explicitly.
        if is_free_function(func.__qualname__):
            if workflow is None:
                msg = f"To decorate {func.__name__} please pass a workflow class to the @step decorator."
                raise WorkflowValidationError(msg)
            workflow.add_step(func)

        return func

    if func is not None:
        # The decorator was used without parentheses, like `@step`
        return decorator(func)
    return decorator