Try catch step

A composite pipeline step that implements try-catch-fallback logic.

This step executes a primary sequence of steps and, if an exception occurs that matches the specified catch filter, transparently switches execution to a fallback branch.

TryCatchStep(name, body, fallback=None, catch=(Exception,), caught_exception_state=None, retry_config=None, error_handler=None, cache=None)

Bases: BaseCompositeStep

A composite step that executes a primary branch and falls back on exception.

This step attempts to execute a primary branch (body). If any step in the body raises an exception that matches the catch filter, execution is diverted to the fallback branch. The exception can optionally be saved to the state.

Attributes:

Name	Type	Description
name	str	A unique identifier for this pipeline step.
body	list[BasePipelineStep]	The primary sequence of steps to execute.
fallback	list[BasePipelineStep]	The sequence of steps to execute on failure.
catch	tuple[type[Exception], ...]	Tuple of exception types to catch.
caught_exception_state	str | None	State key to store the caught exception message.
retry_policy	RetryPolicy | None	Configuration for retry behavior.

Initialize a new TryCatchStep.

Parameters:

Name	Type	Description	Default
name	str	A unique identifier for the pipeline step.	required
body	BasePipelineStep | list[BasePipelineStep]	The primary steps to execute.	required
fallback	BasePipelineStep | list[BasePipelineStep] | None	The steps to execute if the body fails. Defaults to None.	None
catch	tuple[type[Exception], ...]	Exceptions to catch. Defaults to (Exception,).	(Exception,)
caught_exception_state	str | None	State key to store the exception message. Defaults to None.	None
retry_config	RetryConfig | None	Configuration for retry behavior. Defaults to None.	None
error_handler	BaseStepErrorHandler | None	Strategy to handle errors. Defaults to None.	None
cache	CacheConfig | None	Configuration for cache. Defaults to None.	None

Raises:

Type	Description
TypeError	If body is empty, contains invalid items, or if catch is invalid.

apply_exclusions(exclusions)

Applies exclusion logic to this step and its children recursively.

Parameters:

Name	Type	Description	Default
exclusions	ExclusionSet	The exclusions to evaluate.	required

execute(state, runtime, config=None) async

Executes the body branch and falls back if a matching exception occurs.

Parameters:

Name	Type	Description	Default
state	PipelineState	The current state of the pipeline.	required
runtime	Runtime	Runtime information for this step's execution.	required
config	RunnableConfig | None	The runnable configuration.	None

Returns:

Type	Description
dict[str, Any] | None	dict[str, Any] | None: The accumulated state updates.