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prefect.flow_engine

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Functions

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load_flow_run 

load_flow_run(flow_run_id: UUID) -> FlowRun

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load_flow 

load_flow(flow_run: FlowRun) -> Flow[..., Any]

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load_flow_and_flow_run 

load_flow_and_flow_run(flow_run_id: UUID) -> tuple[FlowRun, Flow[..., Any]]

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send_heartbeats_sync 

send_heartbeats_sync(engine: 'FlowRunEngine[Any, Any]') -> Generator[None, None, None]

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send_heartbeats_async 

send_heartbeats_async(engine: 'AsyncFlowRunEngine[Any, Any]') -> AsyncGenerator[None, None]

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run_flow_sync 

run_flow_sync(flow: Flow[P, R], flow_run: Optional[FlowRun] = None, parameters: Optional[Dict[str, Any]] = None, wait_for: Optional[Iterable[PrefectFuture[Any]]] = None, return_type: Literal['state', 'result'] = 'result', context: Optional[dict[str, Any]] = None) -> Union[R, State, None]

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run_flow_async 

run_flow_async(flow: Flow[P, R], flow_run: Optional[FlowRun] = None, parameters: Optional[Dict[str, Any]] = None, wait_for: Optional[Iterable[PrefectFuture[Any]]] = None, return_type: Literal['state', 'result'] = 'result', context: Optional[dict[str, Any]] = None) -> Union[R, State, None]

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run_generator_flow_sync 

run_generator_flow_sync(flow: Flow[P, R], flow_run: Optional[FlowRun] = None, parameters: Optional[Dict[str, Any]] = None, wait_for: Optional[Iterable[PrefectFuture[Any]]] = None, return_type: Literal['state', 'result'] = 'result', context: Optional[dict[str, Any]] = None) -> Generator[R, None, None]

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run_generator_flow_async 

run_generator_flow_async(flow: Flow[P, R], flow_run: Optional[FlowRun] = None, parameters: Optional[Dict[str, Any]] = None, wait_for: Optional[Iterable[PrefectFuture[R]]] = None, return_type: Literal['state', 'result'] = 'result', context: Optional[dict[str, Any]] = None) -> AsyncGenerator[R, None]

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run_flow 

run_flow(flow: Flow[P, R], flow_run: Optional[FlowRun] = None, parameters: Optional[Dict[str, Any]] = None, wait_for: Optional[Iterable[PrefectFuture[R]]] = None, return_type: Literal['state', 'result'] = 'result', error_logger: Optional[logging.Logger] = None, context: Optional[dict[str, Any]] = None) -> R | State | None | Coroutine[Any, Any, R | State | None] | Generator[R, None, None] | AsyncGenerator[R, None]

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run_flow_in_subprocess 

run_flow_in_subprocess(flow: 'Flow[..., Any]', flow_run: 'FlowRun | None' = None, parameters: dict[str, Any] | None = None, wait_for: Iterable[PrefectFuture[Any]] | None = None, context: dict[str, Any] | None = None, env: dict[str, str | None] | None = None) -> multiprocessing.context.SpawnProcess
Run a flow in a subprocess. Note the result of the flow will only be accessible if the flow is configured to persist its result. Args:
  • flow: The flow to run.
  • flow_run: The flow run object containing run metadata.
  • parameters: The parameters to use when invoking the flow.
  • wait_for: The futures to wait for before starting the flow.
  • context: A serialized context to hydrate before running the flow. If not provided, the current context will be used. A serialized context should be provided if this function is called in a separate memory space from the parent run (e.g. in a subprocess or on another machine).
  • env: Additional environment variables to set in the subprocess.
Returns:
  • A multiprocessing.context.SpawnProcess representing the process that is running the flow.

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Classes

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FlowRunTimeoutError

Raised when a flow run exceeds its defined timeout.

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BaseFlowRunEngine

Methods:

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cancel_all_tasks 

cancel_all_tasks(self) -> None

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heartbeat_seconds 

heartbeat_seconds(self) -> Optional[int]
Get the heartbeat interval from settings.

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is_pending 

is_pending(self) -> bool

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is_running 

is_running(self) -> bool

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setup_flow_run_suspension_request 

setup_flow_run_suspension_request(self) -> Generator[FlowRunSuspensionRequest, None, None]

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state 

state(self) -> State

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FlowRunEngine

Methods:

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begin_run 

begin_run(self) -> State

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call_flow_fn 

call_flow_fn(self) -> Union[R, Coroutine[Any, Any, R]]
Convenience method to call the flow function. Returns a coroutine if the flow is async.

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call_hooks 

call_hooks(self, state: Optional[State] = None) -> None

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client 

client(self) -> SyncPrefectClient

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create_flow_run 

create_flow_run(self, client: SyncPrefectClient) -> FlowRun

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handle_cancellation 

handle_cancellation(self, exc: BaseException) -> None
Force this run through Cancelling -> Cancelled. Used when capture_sigterm has determined (via the cancellation listener) that the SIGTERM was the runner asking for cancellation, not an unrelated termination. Transitioning through Cancelling first The same ownership rule also governs on_cancellation / on_crashed hooks: if the engine owns cancellation/crash handling, it must drive the Cancelling -> Cancelled transitions locally; if an external runner owns them, the child should avoid duplicating state history.

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handle_crash 

handle_crash(self, exc: BaseException) -> None

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handle_exception 

handle_exception(self, exc: Exception, msg: Optional[str] = None, result_store: Optional[ResultStore] = None) -> State

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handle_success 

handle_success(self, result: R) -> R

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handle_timeout 

handle_timeout(self, exc: TimeoutError) -> None

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initialize_run 

initialize_run(self)
Enters a client context and creates a flow run if needed.

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load_subflow_run 

load_subflow_run(self, parent_task_run: TaskRun, client: SyncPrefectClient, context: FlowRunContext) -> Union[FlowRun, None]
This method attempts to load an existing flow run for a subflow task run, if appropriate. If the parent task run is in a final state, we return the existing subflow run to avoid re-execution (unless the parent is being rerun and the subflow did not complete, in which case a fresh run is desired). If the parent task run is in a non-final state (e.g. still Running after a process restart), we also look for an existing subflow run to reattach to, preventing duplicate subflow runs from being created under the same parent task run. If no existing flow run is found, or if the subflow should be rerun, then no flow run is returned.

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result 

result(self, raise_on_failure: bool = True) -> 'Union[R, State, None]'

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run_context 

run_context(self)

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set_state 

set_state(self, state: State, force: bool = False) -> State

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setup_run_context 

setup_run_context(self, client: Optional[SyncPrefectClient] = None)

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start 

start(self) -> Generator[None, None, None]

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AsyncFlowRunEngine

Async version of the flow run engine. NOTE: This has not been fully asyncified yet which may lead to async flows not being fully asyncified. Methods:

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begin_run 

begin_run(self) -> State

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call_flow_fn 

call_flow_fn(self) -> Coroutine[Any, Any, R]
Convenience method to call the flow function. Returns a coroutine if the flow is async.

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call_hooks 

call_hooks(self, state: Optional[State] = None) -> None

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client 

client(self) -> PrefectClient

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create_flow_run 

create_flow_run(self, client: PrefectClient) -> FlowRun

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handle_cancellation 

handle_cancellation(self, exc: BaseException) -> None
Force this run through Cancelling -> Cancelled. Async counterpart to FlowRunEngine.handle_cancellation. Shielded from asyncio cancellation so engine-owned transitions always reach the server.

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handle_crash 

handle_crash(self, exc: BaseException) -> None

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handle_exception 

handle_exception(self, exc: Exception, msg: Optional[str] = None, result_store: Optional[ResultStore] = None) -> State

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handle_success 

handle_success(self, result: R) -> R

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handle_timeout 

handle_timeout(self, exc: TimeoutError) -> None

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initialize_run 

initialize_run(self)
Enters a client context and creates a flow run if needed.

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load_subflow_run 

load_subflow_run(self, parent_task_run: TaskRun, client: PrefectClient, context: FlowRunContext) -> Union[FlowRun, None]
This method attempts to load an existing flow run for a subflow task run, if appropriate. If the parent task run is in a final state, we return the existing subflow run to avoid re-execution (unless the parent is being rerun and the subflow did not complete, in which case a fresh run is desired). If the parent task run is in a non-final state (e.g. still Running after a process restart), we also look for an existing subflow run to reattach to, preventing duplicate subflow runs from being created under the same parent task run. If no existing flow run is found, or if the subflow should be rerun, then no flow run is returned.

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result 

result(self, raise_on_failure: bool = True) -> 'Union[R, State, None]'

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run_context 

run_context(self)

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set_state 

set_state(self, state: State, force: bool = False) -> State

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setup_run_context 

setup_run_context(self, client: Optional[PrefectClient] = None)

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start 

start(self) -> AsyncGenerator[None, None]