langchain/docs/docs/how_to/callbacks_attach.ipynb

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    "# How to attach callbacks to a runnable\n",
    "\n",
    ":::info Prerequisites\n",
    "\n",
    "This guide assumes familiarity with the following concepts:\n",
    "\n",
    "- [Callbacks](/docs/concepts/callbacks)\n",
    "- [Custom callback handlers](/docs/how_to/custom_callbacks)\n",
    "- [Chaining runnables](/docs/how_to/sequence)\n",
    "- [Attach runtime arguments to a Runnable](/docs/how_to/binding)\n",
    "\n",
    ":::\n",
    "\n",
    "If you are composing a chain of runnables and want to reuse callbacks across multiple executions, you can attach callbacks with the [`.with_config()`](https://python.langchain.com/api_reference/core/runnables/langchain_core.runnables.base.Runnable.html#langchain_core.runnables.base.Runnable.with_config) method. This saves you the need to pass callbacks in each time you invoke the chain.\n",
    "\n",
    ":::important\n",
    "\n",
    "`with_config()` binds a configuration which will be interpreted as **runtime** configuration. So these callbacks will propagate to all child components.\n",
    ":::\n",
    "\n",
    "Here's an example:"
   ]
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    "# | output: false\n",
    "# | echo: false\n",
    "\n",
    "%pip install -qU langchain langchain_anthropic\n",
    "\n",
    "import getpass\n",
    "import os\n",
    "\n",
    "os.environ[\"ANTHROPIC_API_KEY\"] = getpass.getpass()"
   ]
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     "text": [
      "Chain RunnableSequence started\n",
      "Chain ChatPromptTemplate started\n",
      "Chain ended, outputs: messages=[HumanMessage(content='What is 1 + 2?')]\n",
      "Chat model started\n",
      "Chat model ended, response: generations=[[ChatGeneration(text='1 + 2 = 3', message=AIMessage(content='1 + 2 = 3', response_metadata={'id': 'msg_01NTYMsH9YxkoWsiPYs4Lemn', 'model': 'claude-3-sonnet-20240229', 'stop_reason': 'end_turn', 'stop_sequence': None, 'usage': {'input_tokens': 16, 'output_tokens': 13}}, id='run-d6bcfd72-9c94-466d-bac0-f39e456ad6e3-0'))]] llm_output={'id': 'msg_01NTYMsH9YxkoWsiPYs4Lemn', 'model': 'claude-3-sonnet-20240229', 'stop_reason': 'end_turn', 'stop_sequence': None, 'usage': {'input_tokens': 16, 'output_tokens': 13}} run=None\n",
      "Chain ended, outputs: content='1 + 2 = 3' response_metadata={'id': 'msg_01NTYMsH9YxkoWsiPYs4Lemn', 'model': 'claude-3-sonnet-20240229', 'stop_reason': 'end_turn', 'stop_sequence': None, 'usage': {'input_tokens': 16, 'output_tokens': 13}} id='run-d6bcfd72-9c94-466d-bac0-f39e456ad6e3-0'\n"
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       "AIMessage(content='1 + 2 = 3', response_metadata={'id': 'msg_01NTYMsH9YxkoWsiPYs4Lemn', 'model': 'claude-3-sonnet-20240229', 'stop_reason': 'end_turn', 'stop_sequence': None, 'usage': {'input_tokens': 16, 'output_tokens': 13}}, id='run-d6bcfd72-9c94-466d-bac0-f39e456ad6e3-0')"
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   "source": [
    "from typing import Any, Dict, List\n",
    "\n",
    "from langchain_anthropic import ChatAnthropic\n",
    "from langchain_core.callbacks import BaseCallbackHandler\n",
    "from langchain_core.messages import BaseMessage\n",
    "from langchain_core.outputs import LLMResult\n",
    "from langchain_core.prompts import ChatPromptTemplate\n",
    "\n",
    "\n",
    "class LoggingHandler(BaseCallbackHandler):\n",
    "    def on_chat_model_start(\n",
    "        self, serialized: Dict[str, Any], messages: List[List[BaseMessage]], **kwargs\n",
    "    ) -> None:\n",
    "        print(\"Chat model started\")\n",
    "\n",
    "    def on_llm_end(self, response: LLMResult, **kwargs) -> None:\n",
    "        print(f\"Chat model ended, response: {response}\")\n",
    "\n",
    "    def on_chain_start(\n",
    "        self, serialized: Dict[str, Any], inputs: Dict[str, Any], **kwargs\n",
    "    ) -> None:\n",
    "        print(f\"Chain {serialized.get('name')} started\")\n",
    "\n",
    "    def on_chain_end(self, outputs: Dict[str, Any], **kwargs) -> None:\n",
    "        print(f\"Chain ended, outputs: {outputs}\")\n",
    "\n",
    "\n",
    "callbacks = [LoggingHandler()]\n",
    "llm = ChatAnthropic(model=\"claude-3-sonnet-20240229\")\n",
    "prompt = ChatPromptTemplate.from_template(\"What is 1 + {number}?\")\n",
    "\n",
    "chain = prompt | llm\n",
    "\n",
    "chain_with_callbacks = chain.with_config(callbacks=callbacks)\n",
    "\n",
    "chain_with_callbacks.invoke({\"number\": \"2\"})"
   ]
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The bound callbacks will run for all nested module runs.\n",
    "\n",
    "## Next steps\n",
    "\n",
    "You've now learned how to attach callbacks to a chain.\n",
    "\n",
    "Next, check out the other how-to guides in this section, such as how to [pass callbacks in at runtime](/docs/how_to/callbacks_runtime)."
   ]
  }
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