Class BedrockChat

Convert a runnable to a tool. Return a new instance of RunnableToolLike which contains the runnable, name, description and schema.

Assigns new fields to the dict output of this runnable. Returns a new runnable.

Default implementation of batch, which calls invoke N times. Subclasses should override this method if they can batch more efficiently.

Bind arguments to a Runnable, returning a new Runnable.

Bind tool-like objects to this chat model.

Invokes the chat model with a single input.

Pick keys from the dict output of this runnable. Returns a new runnable.

Create a new runnable sequence that runs each individual runnable in series, piping the output of one runnable into another runnable or runnable-like.

Stream output in chunks.

Generate a stream of events emitted by the internal steps of the runnable.

Use to create an iterator over StreamEvents that provide real-time information about the progress of the runnable, including StreamEvents from intermediate results.

A StreamEvent is a dictionary with the following schema:

• event: string - Event names are of the format: on_[runnable_type]_(start|stream|end).
• name: string - The name of the runnable that generated the event.
• run_id: string - Randomly generated ID associated with the given execution of the runnable that emitted the event. A child runnable that gets invoked as part of the execution of a parent runnable is assigned its own unique ID.
• tags: string[] - The tags of the runnable that generated the event.
• metadata: Record<string, any> - The metadata of the runnable that generated the event.
• data: Record<string, any>

Below is a table that illustrates some events that might be emitted by various chains. Metadata fields have been omitted from the table for brevity. Chain definitions have been included after the table.

ATTENTION This reference table is for the V2 version of the schema.

+----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
| event                | name             | chunk                           | input                                         | output                                          |
+======================+==================+=================================+===============================================+=================================================+
| on_chat_model_start  | [model name]     |                                 | {"messages": [[SystemMessage, HumanMessage]]} |                                                 |
+----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
| on_chat_model_stream | [model name]     | AIMessageChunk(content="hello") |                                               |                                                 |
+----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
| on_chat_model_end    | [model name]     |                                 | {"messages": [[SystemMessage, HumanMessage]]} | AIMessageChunk(content="hello world")           |
+----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
| on_llm_start         | [model name]     |                                 | {'input': 'hello'}                            |                                                 |
+----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
| on_llm_stream        | [model name]     | 'Hello'                         |                                               |                                                 |
+----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
| on_llm_end           | [model name]     |                                 | 'Hello human!'                                |                                                 |
+----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
| on_chain_start       | some_runnable    |                                 |                                               |                                                 |
+----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
| on_chain_stream      | some_runnable    | "hello world!, goodbye world!"  |                                               |                                                 |
+----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
| on_chain_end         | some_runnable    |                                 | [Document(...)]                               | "hello world!, goodbye world!"                  |
+----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
| on_tool_start        | some_tool        |                                 | {"x": 1, "y": "2"}                            |                                                 |
+----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
| on_tool_end          | some_tool        |                                 |                                               | {"x": 1, "y": "2"}                              |
+----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
| on_retriever_start   | [retriever name] |                                 | {"query": "hello"}                            |                                                 |
+----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
| on_retriever_end     | [retriever name] |                                 | {"query": "hello"}                            | [Document(...), ..]                             |
+----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
| on_prompt_start      | [template_name]  |                                 | {"question": "hello"}                         |                                                 |
+----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
| on_prompt_end        | [template_name]  |                                 | {"question": "hello"}                         | ChatPromptValue(messages: [SystemMessage, ...]) |
+----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
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The "on_chain_*" events are the default for Runnables that don't fit one of the above categories.

In addition to the standard events above, users can also dispatch custom events.

Custom events will be only be surfaced with in the v2 version of the API!

A custom event has following format:

+-----------+------+-----------------------------------------------------------------------------------------------------------+
| Attribute | Type | Description                                                                                               |
+===========+======+===========================================================================================================+
| name      | str  | A user defined name for the event.                                                                        |
+-----------+------+-----------------------------------------------------------------------------------------------------------+
| data      | Any  | The data associated with the event. This can be anything, though we suggest making it JSON serializable.  |
+-----------+------+-----------------------------------------------------------------------------------------------------------+
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Here's an example:

import { RunnableLambda } from "@langchain/core/runnables";
import { dispatchCustomEvent } from "@langchain/core/callbacks/dispatch";
// Use this import for web environments that don't support "async_hooks"
// and manually pass config to child runs.
// import { dispatchCustomEvent } from "@langchain/core/callbacks/dispatch/web";

const slowThing = RunnableLambda.from(async (someInput: string) => {
  // Placeholder for some slow operation
  await new Promise((resolve) => setTimeout(resolve, 100));
  await dispatchCustomEvent("progress_event", {
   message: "Finished step 1 of 2",
 });
 await new Promise((resolve) => setTimeout(resolve, 100));
 return "Done";
});

const eventStream = await slowThing.streamEvents("hello world", {
  version: "v2",
});

for await (const event of eventStream) {
 if (event.event === "on_custom_event") {
   console.log(event);
 }
}
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Stream all output from a runnable, as reported to the callback system. This includes all inner runs of LLMs, Retrievers, Tools, etc. Output is streamed as Log objects, which include a list of jsonpatch ops that describe how the state of the run has changed in each step, and the final state of the run. The jsonpatch ops can be applied in order to construct state.

Default implementation of transform, which buffers input and then calls stream. Subclasses should override this method if they can start producing output while input is still being generated.

Bind config to a Runnable, returning a new Runnable.

Create a new runnable from the current one that will try invoking other passed fallback runnables if the initial invocation fails.

Bind lifecycle listeners to a Runnable, returning a new Runnable. The Run object contains information about the run, including its id, type, input, output, error, startTime, endTime, and any tags or metadata added to the run.

Add retry logic to an existing runnable.

Model wrapper that returns outputs formatted to match the given schema.

Model wrapper that returns outputs formatted to match the given schema.