langchain_core.callbacks.base.BaseCallbackHandler

class langchain_core.callbacks.base.BaseCallbackHandler

Base callback handler for LangChain.

Attributes

ignore_agent	Whether to ignore agent callbacks.
ignore_chain	Whether to ignore chain callbacks.
ignore_chat_model	Whether to ignore chat model callbacks.
ignore_custom_event	Ignore custom event.
ignore_llm	Whether to ignore LLM callbacks.
ignore_retriever	Whether to ignore retriever callbacks.
ignore_retry	Whether to ignore retry callbacks.
raise_error	Whether to raise an error if an exception occurs.
run_inline	Whether to run the callback inline.

Methods

__init__()
on_agent_action(action, *, run_id[, ...])	Run on agent action.
on_agent_finish(finish, *, run_id[, ...])	Run on the agent end.
on_chain_end(outputs, *, run_id[, parent_run_id])	Run when chain ends running.
on_chain_error(error, *, run_id[, parent_run_id])	Run when chain errors.
on_chain_start(serialized, inputs, *, run_id)	Run when a chain starts running.
on_chat_model_start(serialized, messages, *, ...)	Run when a chat model starts running.
on_custom_event(name, data, *, run_id[, ...])	Override to define a handler for a custom event.
on_llm_end(response, *, run_id[, parent_run_id])	Run when LLM ends running.
on_llm_error(error, *, run_id[, parent_run_id])	Run when LLM errors.
on_llm_new_token(token, *[, chunk, ...])	Run on new LLM token.
on_llm_start(serialized, prompts, *, run_id)	Run when LLM starts running.
on_retriever_end(documents, *, run_id[, ...])	Run when Retriever ends running.
on_retriever_error(error, *, run_id[, ...])	Run when Retriever errors.
on_retriever_start(serialized, query, *, run_id)	Run when the Retriever starts running.
on_retry(retry_state, *, run_id[, parent_run_id])	Run on a retry event.
on_text(text, *, run_id[, parent_run_id])	Run on an arbitrary text.
on_tool_end(output, *, run_id[, parent_run_id])	Run when the tool ends running.
on_tool_error(error, *, run_id[, parent_run_id])	Run when tool errors.
on_tool_start(serialized, input_str, *, run_id)	Run when the tool starts running.

__init__()

on_agent_action(action: AgentAction, *, run_id: UUID, parent_run_id: Optional[UUID] = None, **kwargs: Any) → Any

Run on agent action.

Parameters

• action (AgentAction) – The agent action.

• run_id (UUID) – The run ID. This is the ID of the current run.

• parent_run_id (UUID) – The parent run ID. This is the ID of the parent run.

• kwargs (Any) – Additional keyword arguments.

Return type

Any

on_agent_finish(finish: AgentFinish, *, run_id: UUID, parent_run_id: Optional[UUID] = None, **kwargs: Any) → Any

Run on the agent end.

Parameters

• finish (AgentFinish) – The agent finish.

• run_id (UUID) – The run ID. This is the ID of the current run.

• parent_run_id (UUID) – The parent run ID. This is the ID of the parent run.

• kwargs (Any) – Additional keyword arguments.

Return type

Any

on_chain_end(outputs: Dict[str, Any], *, run_id: UUID, parent_run_id: Optional[UUID] = None, **kwargs: Any) → Any

Run when chain ends running.

Parameters

• outputs (Dict[str, Any]) – The outputs of the chain.

• run_id (UUID) – The run ID. This is the ID of the current run.

• parent_run_id (UUID) – The parent run ID. This is the ID of the parent run.

• kwargs (Any) – Additional keyword arguments.

Return type

Any

on_chain_error(error: BaseException, *, run_id: UUID, parent_run_id: Optional[UUID] = None, **kwargs: Any) → Any

Run when chain errors.

Parameters

• error (BaseException) – The error that occurred.

• run_id (UUID) – The run ID. This is the ID of the current run.

• parent_run_id (UUID) – The parent run ID. This is the ID of the parent run.

• kwargs (Any) – Additional keyword arguments.

Return type

Any

on_chain_start(serialized: Dict[str, Any], inputs: Dict[str, Any], *, run_id: UUID, parent_run_id: Optional[UUID] = None, tags: Optional[List[str]] = None, metadata: Optional[Dict[str, Any]] = None, **kwargs: Any) → Any

Run when a chain starts running.

Parameters

• serialized (Dict[str, Any]) – The serialized chain.

• inputs (Dict[str, Any]) – The inputs.

• run_id (UUID) – The run ID. This is the ID of the current run.

• parent_run_id (UUID) – The parent run ID. This is the ID of the parent run.

• tags (Optional[List[str]]) – The tags.

• metadata (Optional[Dict[str, Any]]) – The metadata.

• kwargs (Any) – Additional keyword arguments.

Return type

Any

on_chat_model_start(serialized: Dict[str, Any], messages: List[List[BaseMessage]], *, run_id: UUID, parent_run_id: Optional[UUID] = None, tags: Optional[List[str]] = None, metadata: Optional[Dict[str, Any]] = None, **kwargs: Any) → Any

Run when a chat model starts running.

ATTENTION: This method is called for chat models. If you’re implementing

a handler for a non-chat model, you should use on_llm_start instead.

Parameters

• serialized (Dict[str, Any]) – The serialized chat model.

• messages (List[List[BaseMessage]]) – The messages.

• run_id (UUID) – The run ID. This is the ID of the current run.

• parent_run_id (UUID) – The parent run ID. This is the ID of the parent run.

• tags (Optional[List[str]]) – The tags.

• metadata (Optional[Dict[str, Any]]) – The metadata.

• kwargs (Any) – Additional keyword arguments.

Return type

Any

on_custom_event(name: str, data: Any, *, run_id: UUID, tags: Optional[List[str]] = None, metadata: Optional[Dict[str, Any]] = None, **kwargs: Any) → Any

Override to define a handler for a custom event.

Parameters

• name (str) – The name of the custom event.

• data (Any) – The data for the custom event. Format will match the format specified by the user.

• run_id (UUID) – The ID of the run.

• tags (Optional[List[str]]) – The tags associated with the custom event (includes inherited tags).

• metadata (Optional[Dict[str, Any]]) – The metadata associated with the custom event (includes inherited metadata).

• kwargs (Any) –

Return type

Any

New in version 0.2.15.

on_llm_end(response: LLMResult, *, run_id: UUID, parent_run_id: Optional[UUID] = None, **kwargs: Any) → Any

Run when LLM ends running.

Parameters

• response (LLMResult) – The response which was generated.

• run_id (UUID) – The run ID. This is the ID of the current run.

• parent_run_id (UUID) – The parent run ID. This is the ID of the parent run.

• kwargs (Any) – Additional keyword arguments.

Return type

Any

on_llm_error(error: BaseException, *, run_id: UUID, parent_run_id: Optional[UUID] = None, **kwargs: Any) → Any

Run when LLM errors.

Parameters

• error (BaseException) – The error that occurred.

• run_id (UUID) – The run ID. This is the ID of the current run.

• parent_run_id (UUID) – The parent run ID. This is the ID of the parent run.

• kwargs (Any) – Additional keyword arguments.

Return type

Any

on_llm_new_token(token: str, *, chunk: Optional[Union[GenerationChunk, ChatGenerationChunk]] = None, run_id: UUID, parent_run_id: Optional[UUID] = None, **kwargs: Any) → Any

Run on new LLM token. Only available when streaming is enabled.

Parameters

• token (str) – The new token.

• chunk (GenerationChunk | ChatGenerationChunk) – The new generated chunk, containing content and other information.

• run_id (UUID) – The run ID. This is the ID of the current run.

• parent_run_id (UUID) – The parent run ID. This is the ID of the parent run.

• kwargs (Any) – Additional keyword arguments.

Return type

Any

on_llm_start(serialized: Dict[str, Any], prompts: List[str], *, run_id: UUID, parent_run_id: Optional[UUID] = None, tags: Optional[List[str]] = None, metadata: Optional[Dict[str, Any]] = None, **kwargs: Any) → Any

Run when LLM starts running.

ATTENTION: This method is called for non-chat models (regular LLMs). If

you’re implementing a handler for a chat model, you should use on_chat_model_start instead.

Parameters

• serialized (Dict[str, Any]) – The serialized LLM.

• prompts (List[str]) – The prompts.

• run_id (UUID) – The run ID. This is the ID of the current run.

• parent_run_id (UUID) – The parent run ID. This is the ID of the parent run.

• tags (Optional[List[str]]) – The tags.

• metadata (Optional[Dict[str, Any]]) – The metadata.

• kwargs (Any) – Additional keyword arguments.

Return type

Any

on_retriever_end(documents: Sequence[Document], *, run_id: UUID, parent_run_id: Optional[UUID] = None, **kwargs: Any) → Any

Run when Retriever ends running.

Parameters

• documents (Sequence[Document]) – The documents retrieved.

• run_id (UUID) – The run ID. This is the ID of the current run.

• parent_run_id (UUID) – The parent run ID. This is the ID of the parent run.

• kwargs (Any) – Additional keyword arguments.

Return type

Any

on_retriever_error(error: BaseException, *, run_id: UUID, parent_run_id: Optional[UUID] = None, **kwargs: Any) → Any

Run when Retriever errors.

Parameters

• error (BaseException) – The error that occurred.

• run_id (UUID) – The run ID. This is the ID of the current run.

• parent_run_id (UUID) – The parent run ID. This is the ID of the parent run.

• kwargs (Any) – Additional keyword arguments.

Return type

Any

on_retriever_start(serialized: Dict[str, Any], query: str, *, run_id: UUID, parent_run_id: Optional[UUID] = None, tags: Optional[List[str]] = None, metadata: Optional[Dict[str, Any]] = None, **kwargs: Any) → Any

Run when the Retriever starts running.

Parameters

• serialized (Dict[str, Any]) – The serialized Retriever.

• query (str) – The query.

• run_id (UUID) – The run ID. This is the ID of the current run.

• parent_run_id (UUID) – The parent run ID. This is the ID of the parent run.

• tags (Optional[List[str]]) – The tags.

• metadata (Optional[Dict[str, Any]]) – The metadata.

• kwargs (Any) – Additional keyword arguments.

Return type

Any

on_retry(retry_state: RetryCallState, *, run_id: UUID, parent_run_id: Optional[UUID] = None, **kwargs: Any) → Any

Run on a retry event.

Parameters

• retry_state (RetryCallState) – The retry state.

• run_id (UUID) – The run ID. This is the ID of the current run.

• parent_run_id (UUID) – The parent run ID. This is the ID of the parent run.

• kwargs (Any) – Additional keyword arguments.

Return type

Any

on_text(text: str, *, run_id: UUID, parent_run_id: Optional[UUID] = None, **kwargs: Any) → Any

Run on an arbitrary text.

Parameters

• text (str) – The text.

• run_id (UUID) – The run ID. This is the ID of the current run.

• parent_run_id (UUID) – The parent run ID. This is the ID of the parent run.

• kwargs (Any) – Additional keyword arguments.

Return type

Any

on_tool_end(output: Any, *, run_id: UUID, parent_run_id: Optional[UUID] = None, **kwargs: Any) → Any

Run when the tool ends running.

Parameters

• output (Any) – The output of the tool.

• run_id (UUID) – The run ID. This is the ID of the current run.

• parent_run_id (UUID) – The parent run ID. This is the ID of the parent run.

• kwargs (Any) – Additional keyword arguments.

Return type

Any

on_tool_error(error: BaseException, *, run_id: UUID, parent_run_id: Optional[UUID] = None, **kwargs: Any) → Any

Run when tool errors.

Parameters

• error (BaseException) – The error that occurred.

• run_id (UUID) – The run ID. This is the ID of the current run.

• parent_run_id (UUID) – The parent run ID. This is the ID of the parent run.

• kwargs (Any) – Additional keyword arguments.

Return type

Any

on_tool_start(serialized: Dict[str, Any], input_str: str, *, run_id: UUID, parent_run_id: Optional[UUID] = None, tags: Optional[List[str]] = None, metadata: Optional[Dict[str, Any]] = None, inputs: Optional[Dict[str, Any]] = None, **kwargs: Any) → Any

Run when the tool starts running.

Parameters

• serialized (Dict[str, Any]) – The serialized tool.

• input_str (str) – The input string.

• run_id (UUID) – The run ID. This is the ID of the current run.

• parent_run_id (UUID) – The parent run ID. This is the ID of the parent run.

• tags (Optional[List[str]]) – The tags.

• metadata (Optional[Dict[str, Any]]) – The metadata.

• inputs (Optional[Dict[str, Any]]) – The inputs.

• kwargs (Any) – Additional keyword arguments.

Return type

Any

Examples using BaseCallbackHandler

• How to attach callbacks to a runnable

• How to create custom callback handlers

• How to pass callbacks in at runtime

• How to propagate callbacks constructor

• How to use callbacks in async environments