community: Add CometLLM tracing context var (#15765)

I also added LANGCHAIN_COMET_TRACING to enable the CometLLM tracing
integration similar to other tracing integrations. This is easier for
end-users to enable it rather than importing the callback and pass it
manually.

(This is the same content as
https://github.com/langchain-ai/langchain/pull/14650 but rebased and
squashed as something seems to confuse Github Action).

docs/docs/integrations/callbacks/comet_tracing.ipynb

@@ -0,0 +1,138 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "id": "5371a9bb",
+   "metadata": {},
+   "source": [
+    "# Comet Tracing\n",
+    "\n",
+    "There are two ways to trace your LangChains executions with Comet:\n",
+    "\n",
+    "1. Setting the `LANGCHAIN_COMET_TRACING` environment variable to \"true\". This is the recommended way.\n",
+    "2. Import the `CometTracer` manually and pass it explicitely."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "17c04cc6-c93d-4b6c-a033-e897577f4ed1",
+   "metadata": {
+    "ExecuteTime": {
+     "end_time": "2023-05-18T12:47:46.580776Z",
+     "start_time": "2023-05-18T12:47:46.577833Z"
+    },
+    "tags": []
+   },
+   "outputs": [],
+   "source": [
+    "import os\n",
+    "\n",
+    "import comet_llm\n",
+    "\n",
+    "os.environ[\"LANGCHAIN_COMET_TRACING\"] = \"true\"\n",
+    "\n",
+    "# Connect to Comet if no API Key is set\n",
+    "comet_llm.init()\n",
+    "\n",
+    "# comet documentation to configure comet using env variables\n",
+    "# https://www.comet.com/docs/v2/api-and-sdk/llm-sdk/configuration/\n",
+    "# here we are configuring the comet project\n",
+    "os.environ[\"COMET_PROJECT_NAME\"] = \"comet-example-langchain-tracing\"\n",
+    "\n",
+    "from langchain.agents import AgentType, initialize_agent, load_tools\n",
+    "from langchain.llms import OpenAI"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "1b62cd48",
+   "metadata": {
+    "ExecuteTime": {
+     "end_time": "2023-05-18T12:47:47.445229Z",
+     "start_time": "2023-05-18T12:47:47.436424Z"
+    },
+    "tags": []
+   },
+   "outputs": [],
+   "source": [
+    "# Agent run with tracing. Ensure that OPENAI_API_KEY is set appropriately to run this example.\n",
+    "\n",
+    "llm = OpenAI(temperature=0)\n",
+    "tools = load_tools([\"llm-math\"], llm=llm)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "bfa16b79-aa4b-4d41-a067-70d1f593f667",
+   "metadata": {
+    "ExecuteTime": {
+     "end_time": "2023-05-18T12:48:01.816137Z",
+     "start_time": "2023-05-18T12:47:49.109574Z"
+    },
+    "tags": []
+   },
+   "outputs": [],
+   "source": [
+    "agent = initialize_agent(\n",
+    "    tools, llm, agent=AgentType.ZERO_SHOT_REACT_DESCRIPTION, verbose=True\n",
+    ")\n",
+    "\n",
+    "agent.run(\"What is 2 raised to .123243 power?\")  # this should be traced\n",
+    "# An url for the chain like the following should print in your console:\n",
+    "# https://www.comet.com/<workspace>/<project_name>\n",
+    "# The url can be used to view the LLM chain in Comet."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "5e212e7d",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# Now, we unset the environment variable and use a context manager.\n",
+    "if \"LANGCHAIN_COMET_TRACING\" in os.environ:\n",
+    "    del os.environ[\"LANGCHAIN_COMET_TRACING\"]\n",
+    "\n",
+    "from langchain.callbacks.tracers.comet import CometTracer\n",
+    "\n",
+    "tracer = CometTracer()\n",
+    "\n",
+    "# Recreate the LLM, tools and agent and passing the callback to each of them\n",
+    "llm = OpenAI(temperature=0)\n",
+    "tools = load_tools([\"llm-math\"], llm=llm)\n",
+    "agent = initialize_agent(\n",
+    "    tools, llm, agent=AgentType.ZERO_SHOT_REACT_DESCRIPTION, verbose=True\n",
+    ")\n",
+    "\n",
+    "agent.run(\n",
+    "    \"What is 2 raised to .123243 power?\", callbacks=[tracer]\n",
+    ")  # this should be traced"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3 (ipykernel)",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.9.1"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}

libs/community/langchain_community/callbacks/manager.py

@@ -11,6 +11,7 @@ from typing import (
 from langchain_core.tracers.context import register_configure_hook
 
 from langchain_community.callbacks.openai_info import OpenAICallbackHandler
+from langchain_community.callbacks.tracers.comet import CometTracer
 from langchain_community.callbacks.tracers.wandb import WandbTracer
 
 logger = logging.getLogger(__name__)
@@ -21,11 +22,17 @@ openai_callback_var: ContextVar[Optional[OpenAICallbackHandler]] = ContextVar(
 wandb_tracing_callback_var: ContextVar[Optional[WandbTracer]] = ContextVar(  # noqa: E501
     "tracing_wandb_callback", default=None
 )
+comet_tracing_callback_var: ContextVar[Optional[CometTracer]] = ContextVar(  # noqa: E501
+    "tracing_comet_callback", default=None
+)
 
 register_configure_hook(openai_callback_var, True)
 register_configure_hook(
     wandb_tracing_callback_var, True, WandbTracer, "LANGCHAIN_WANDB_TRACING"
 )
+register_configure_hook(
+    comet_tracing_callback_var, True, CometTracer, "LANGCHAIN_COMET_TRACING"
+)
 
 
 @contextmanager