Run when a chat model starts running.
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.
When overriding this method, the signature must include the two
required positional arguments serialized and messages. Avoid
using *args in your override — doing so causes an IndexError
in the fallback path when the callback system converts messages
to prompt strings for on_llm_start. Always declare the
signature explicitly:
.. code-block:: python
def on_chat_model_start(
self,
serialized: dict[str, Any],
messages: list[list[BaseMessage]],
**kwargs: Any,
) -> None:
raise NotImplementedError # triggers fallback to on_llm_start
on_chat_model_start(
self,
serialized: dict[str, Any],
messages: list[list[BaseMessage]],
*,
run_id: UUID,
parent_run_id: UUID | None = None,
tags: list[str] | None = None,
metadata: dict[str, Any] | None = None,
**kwargs: Any = {}
) -> Any| Name | Type | Description |
|---|---|---|
serialized* | dict[str, Any] | The serialized chat model. |
messages* | list[list[BaseMessage]] | The messages. Must be a list of message lists — this is a required positional argument and must be present in any override. |
run_id* | UUID | The ID of the current run. |
parent_run_id | UUID | None | Default: NoneThe ID of the parent run. |
tags | list[str] | None | Default: NoneThe tags. |
metadata | dict[str, Any] | None | Default: NoneThe metadata. |
**kwargs | Any | Default: {}Additional keyword arguments. |