构建代理

LangChain 支持创建智能体，即使用大型语言模型作为推理引擎来决定采取哪些行动以及执行行动所需的输入。执行行动后，可以将结果反馈给大型语言模型，以判断是否需要更多行动，或者是否可以结束。这通常通过工具调用实现。

在本教程中，我们将构建一个可以与搜索引擎交互的智能体。你将能够向这个智能体提问，观察它调用搜索工具，并与它进行对话。

端到端智能体

以下代码片段展示了一个功能完备的智能体，它使用大型语言模型来决定使用哪些工具。它配备了一个通用搜索工具。它具有对话记忆功能——这意味着它可以作为一个多轮聊天机器人使用。

在本指南的其余部分，我们将详细介绍各个组件及其功能——但如果你只想获取代码并开始使用，请随意使用！

# Import relevant functionality
from langchain.chat_models import init_chat_model
from langchain_tavily import TavilySearch
from langgraph.checkpoint.memory import MemorySaver
from langgraph.prebuilt import create_react_agent

# Create the agent
memory = MemorySaver()
model = init_chat_model("anthropic:claude-3-5-sonnet-latest")
search = TavilySearch(max_results=2)
tools = [search]
agent_executor = create_react_agent(model, tools, checkpointer=memory)

API 参考:init_chat_model | MemorySaver | create_react_agent

# Use the agent
config = {"configurable": {"thread_id": "abc123"}}

input_message = {
    "role": "user",
    "content": "Hi, I'm Bob and I live in SF.",
}
for step in agent_executor.stream(
    {"messages": [input_message]}, config, stream_mode="values"
):
    step["messages"][-1].pretty_print()

================================[1m Human Message [0m=================================

Hi, I'm Bob and I live in SF.
==================================[1m Ai Message [0m==================================

Hello Bob! I notice you've introduced yourself and mentioned you live in SF (San Francisco), but you haven't asked a specific question or made a request that requires the use of any tools. Is there something specific you'd like to know about San Francisco or any other topic? I'd be happy to help you find information using the available search tools.

input_message = {
    "role": "user",
    "content": "What's the weather where I live?",
}

for step in agent_executor.stream(
    {"messages": [input_message]}, config, stream_mode="values"
):
    step["messages"][-1].pretty_print()

================================[1m Human Message [0m=================================

What's the weather where I live?
==================================[1m Ai Message [0m==================================

[{'text': 'Let me search for current weather information in San Francisco.', 'type': 'text'}, {'id': 'toolu_011kSdheoJp8THURoLmeLtZo', 'input': {'query': 'current weather San Francisco CA'}, 'name': 'tavily_search', 'type': 'tool_use'}]
Tool Calls:
  tavily_search (toolu_011kSdheoJp8THURoLmeLtZo)
 Call ID: toolu_011kSdheoJp8THURoLmeLtZo
  Args:
    query: current weather San Francisco CA
=================================[1m Tool Message [0m=================================
Name: tavily_search

{"query": "current weather San Francisco CA", "follow_up_questions": null, "answer": null, "images": [], "results": [{"title": "Weather in San Francisco, CA", "url": "https://www.weatherapi.com/", "content": "{'location': {'name': 'San Francisco', 'region': 'California', 'country': 'United States of America', 'lat': 37.775, 'lon': -122.4183, 'tz_id': 'America/Los_Angeles', 'localtime_epoch': 1750168606, 'localtime': '2025-06-17 06:56'}, 'current': {'last_updated_epoch': 1750167900, 'last_updated': '2025-06-17 06:45', 'temp_c': 11.7, 'temp_f': 53.1, 'is_day': 1, 'condition': {'text': 'Fog', 'icon': '//cdn.weatherapi.com/weather/64x64/day/248.png', 'code': 1135}, 'wind_mph': 4.0, 'wind_kph': 6.5, 'wind_degree': 215, 'wind_dir': 'SW', 'pressure_mb': 1017.0, 'pressure_in': 30.02, 'precip_mm': 0.0, 'precip_in': 0.0, 'humidity': 86, 'cloud': 0, 'feelslike_c': 11.3, 'feelslike_f': 52.4, 'windchill_c': 8.7, 'windchill_f': 47.7, 'heatindex_c': 9.8, 'heatindex_f': 49.7, 'dewpoint_c': 9.6, 'dewpoint_f': 49.2, 'vis_km': 16.0, 'vis_miles': 9.0, 'uv': 0.0, 'gust_mph': 6.3, 'gust_kph': 10.2}}", "score": 0.944705, "raw_content": null}, {"title": "Weather in San Francisco in June 2025", "url": "https://world-weather.info/forecast/usa/san_francisco/june-2025/", "content": "Detailed ⚡ San Francisco Weather Forecast for June 2025 - day/night 🌡️ temperatures, precipitations - World-Weather.info. Add the current city. Search. Weather; Archive; Weather Widget °F. World; United States; California; Weather in San Francisco; ... 17 +64° +54° 18 +61° +54° 19", "score": 0.86441374, "raw_content": null}], "response_time": 2.34}
==================================[1m Ai Message [0m==================================

Based on the search results, here's the current weather in San Francisco:
- Temperature: 53.1°F (11.7°C)
- Condition: Foggy
- Wind: 4.0 mph from the Southwest
- Humidity: 86%
- Visibility: 9 miles

This is quite typical weather for San Francisco, with the characteristic fog that the city is known for. Would you like to know anything else about the weather or San Francisco in general?

设置

Jupyter Notebook

本指南（以及文档中的大多数其他指南）使用Jupyter Notebook并假定读者也使用它。Jupyter Notebook 是学习如何使用大型语言模型系统的完美交互式环境，因为通常会出现问题（意外输出、API 不可用等），而观察这些情况是更好地理解如何构建大型语言模型的好方法。

本教程和其他教程或许在Jupyter Notebook中运行最为方便。有关如何安装的说明，请参见此处。

安装

要安装 LangChain，请运行

%pip install -U langgraph langchain-tavily langgraph-checkpoint-sqlite

更多详情，请参阅我们的安装指南。

LangSmith

你使用 LangChain 构建的许多应用程序将包含多个步骤，其中包含对大型语言模型调用的多次调用。随着这些应用程序变得越来越复杂，能够检查你的链或智能体内部到底发生了什么变得至关重要。做到这一点的最佳方法是使用LangSmith。

在上述链接注册后，请务必设置您的环境变量以开始记录跟踪日志

export LANGSMITH_TRACING="true"
export LANGSMITH_API_KEY="..."

或者，如果在Notebook中，您可以这样设置

import getpass
import os

os.environ["LANGSMITH_TRACING"] = "true"
os.environ["LANGSMITH_API_KEY"] = getpass.getpass()

Tavily

我们将使用Tavily（一个搜索引擎）作为工具。要使用它，你需要获取并设置一个 API 密钥

export TAVILY_API_KEY="..."

或者，如果在 Notebook 中，你可以通过以下方式设置：

import getpass
import os

os.environ["TAVILY_API_KEY"] = getpass.getpass()

定义工具

我们首先需要创建要使用的工具。我们选择的主要工具将是Tavily——一个搜索引擎。我们可以使用专门的langchain-tavily 集成包，以便轻松地将 Tavily 搜索引擎作为工具与 LangChain 结合使用。

from langchain_tavily import TavilySearch

search = TavilySearch(max_results=2)
search_results = search.invoke("What is the weather in SF")
print(search_results)
# If we want, we can create other tools.
# Once we have all the tools we want, we can put them in a list that we will reference later.
tools = [search]

{'query': 'What is the weather in SF', 'follow_up_questions': None, 'answer': None, 'images': [], 'results': [{'title': 'Weather in San Francisco, CA', 'url': 'https://www.weatherapi.com/', 'content': "{'location': {'name': 'San Francisco', 'region': 'California', 'country': 'United States of America', 'lat': 37.775, 'lon': -122.4183, 'tz_id': 'America/Los_Angeles', 'localtime_epoch': 1750168606, 'localtime': '2025-06-17 06:56'}, 'current': {'last_updated_epoch': 1750167900, 'last_updated': '2025-06-17 06:45', 'temp_c': 11.7, 'temp_f': 53.1, 'is_day': 1, 'condition': {'text': 'Fog', 'icon': '//cdn.weatherapi.com/weather/64x64/day/248.png', 'code': 1135}, 'wind_mph': 4.0, 'wind_kph': 6.5, 'wind_degree': 215, 'wind_dir': 'SW', 'pressure_mb': 1017.0, 'pressure_in': 30.02, 'precip_mm': 0.0, 'precip_in': 0.0, 'humidity': 86, 'cloud': 0, 'feelslike_c': 11.3, 'feelslike_f': 52.4, 'windchill_c': 8.7, 'windchill_f': 47.7, 'heatindex_c': 9.8, 'heatindex_f': 49.7, 'dewpoint_c': 9.6, 'dewpoint_f': 49.2, 'vis_km': 16.0, 'vis_miles': 9.0, 'uv': 0.0, 'gust_mph': 6.3, 'gust_kph': 10.2}}", 'score': 0.9185379, 'raw_content': None}, {'title': 'Weather in San Francisco in June 2025', 'url': 'https://world-weather.info/forecast/usa/san_francisco/june-2025/', 'content': "Weather in San Francisco in June 2025 (California) - Detailed Weather Forecast for a Month *   Weather in San Francisco Weather in San Francisco in June 2025 *   1 +63° +55° *   2 +66° +54° *   3 +66° +55° *   4 +66° +54° *   5 +66° +55° *   6 +66° +57° *   7 +64° +55° *   8 +63° +55° *   9 +63° +54° *   10 +59° +54° *   11 +59° +54° *   12 +61° +54° Weather in Washington, D.C.**+68°** Sacramento**+81°** Pleasanton**+72°** Redwood City**+68°** San Leandro**+61°** San Mateo**+64°** San Rafael**+70°** San Ramon**+64°** South San Francisco**+61°** Daly City**+59°** Wilder**+66°** Woodacre**+70°** world's temperature today Colchani day+50°F night+16°F Az Zubayr day+124°F night+93°F Weather forecast on your site Install _San Francisco_ +61° Temperature units", 'score': 0.7978881, 'raw_content': None}], 'response_time': 2.62}

提示

在许多应用程序中，你可能希望定义自定义工具。LangChain 支持通过 Python 函数和其他方式创建自定义工具。详情请参阅如何创建工具指南。

使用语言模型

接下来，让我们学习如何使用语言模型来调用工具。LangChain 支持多种不同的语言模型，你可以互换使用——请在下面选择你想要使用的模型！

选择聊天模型

pip install -qU "langchain[google-genai]"

import getpass
import os

if not os.environ.get("GOOGLE_API_KEY"):
  os.environ["GOOGLE_API_KEY"] = getpass.getpass("Enter API key for Google Gemini: ")

from langchain.chat_models import init_chat_model

model = init_chat_model("gemini-2.0-flash", model_provider="google_genai")

你可以通过传入消息列表来调用语言模型。默认情况下，响应是一个content字符串。

query = "Hi!"
response = model.invoke([{"role": "user", "content": query}])
response.text()

'Hello! How can I help you today?'

我们现在可以看看如何启用这个模型进行工具调用。为此，我们使用.bind_tools来让语言模型了解这些工具

model_with_tools = model.bind_tools(tools)

我们现在可以调用模型了。让我们首先用一条普通消息调用它，看看它如何响应。我们可以查看content字段以及tool_calls字段。

query = "Hi!"
response = model_with_tools.invoke([{"role": "user", "content": query}])

print(f"Message content: {response.text()}\n")
print(f"Tool calls: {response.tool_calls}")

Message content: Hello! I'm here to help you. I have access to a powerful search tool that can help answer questions and find information about various topics. What would you like to know about?

Feel free to ask any question or request information, and I'll do my best to assist you using the available tools.

Tool calls: []

现在，让我们尝试使用一些预期会调用工具的输入来调用它。

query = "Search for the weather in SF"
response = model_with_tools.invoke([{"role": "user", "content": query}])

print(f"Message content: {response.text()}\n")
print(f"Tool calls: {response.tool_calls}")

Message content: I'll help you search for information about the weather in San Francisco.

Tool calls: [{'name': 'tavily_search', 'args': {'query': 'current weather San Francisco'}, 'id': 'toolu_015gdPn1jbB2Z21DmN2RAnti', 'type': 'tool_call'}]

我们可以看到现在没有文本内容，但有一个工具调用！它要求我们调用 Tavily 搜索工具。

这还没有实际调用该工具——它只是在告诉我们应该调用。为了实际调用它，我们需要创建我们的智能体。

创建智能体

现在我们已经定义了工具和大型语言模型，我们可以创建智能体了。我们将使用LangGraph来构建智能体。目前，我们正在使用一个高级接口来构建智能体，但 LangGraph 的优点在于，这个高级接口由一个低级别、高度可控的 API 支持，以防你想要修改智能体逻辑。

现在，我们可以使用大型语言模型和工具初始化智能体。

请注意，我们传入的是model，而不是model_with_tools。这是因为create_react_agent将在底层为我们调用.bind_tools。

from langgraph.prebuilt import create_react_agent

agent_executor = create_react_agent(model, tools)

API 参考：create_react_agent

运行智能体

我们现在可以运行智能体并进行一些查询了！请注意，目前这些查询都是无状态的查询（它不会记住之前的交互）。请注意，智能体将在交互结束时返回最终状态（其中包含任何输入，我们稍后将了解如何仅获取输出）。

首先，让我们看看在不需要调用工具时它是如何响应的

input_message = {"role": "user", "content": "Hi!"}
response = agent_executor.invoke({"messages": [input_message]})

for message in response["messages"]:
    message.pretty_print()

================================[1m Human Message [0m=================================

Hi!
==================================[1m Ai Message [0m==================================

Hello! I'm here to help you with your questions using the available search tools. Please feel free to ask any question, and I'll do my best to find relevant and accurate information for you.

为了准确了解幕后发生的事情（并确保它没有调用工具），我们可以查看LangSmith 追踪

现在，让我们在一个应该调用工具的示例上尝试一下

input_message = {"role": "user", "content": "Search for the weather in SF"}
response = agent_executor.invoke({"messages": [input_message]})

for message in response["messages"]:
    message.pretty_print()

================================[1m Human Message [0m=================================

Search for the weather in SF
==================================[1m Ai Message [0m==================================

[{'text': "I'll help you search for weather information in San Francisco. Let me use the search engine to find current weather conditions.", 'type': 'text'}, {'id': 'toolu_01WWcXGnArosybujpKzdmARZ', 'input': {'query': 'current weather San Francisco SF'}, 'name': 'tavily_search', 'type': 'tool_use'}]
Tool Calls:
  tavily_search (toolu_01WWcXGnArosybujpKzdmARZ)
 Call ID: toolu_01WWcXGnArosybujpKzdmARZ
  Args:
    query: current weather San Francisco SF
=================================[1m Tool Message [0m=================================
Name: tavily_search

{"query": "current weather San Francisco SF", "follow_up_questions": null, "answer": null, "images": [], "results": [{"title": "Weather in San Francisco, CA", "url": "https://www.weatherapi.com/", "content": "{'location': {'name': 'San Francisco', 'region': 'California', 'country': 'United States of America', 'lat': 37.775, 'lon': -122.4183, 'tz_id': 'America/Los_Angeles', 'localtime_epoch': 1750168606, 'localtime': '2025-06-17 06:56'}, 'current': {'last_updated_epoch': 1750167900, 'last_updated': '2025-06-17 06:45', 'temp_c': 11.7, 'temp_f': 53.1, 'is_day': 1, 'condition': {'text': 'Fog', 'icon': '//cdn.weatherapi.com/weather/64x64/day/248.png', 'code': 1135}, 'wind_mph': 4.0, 'wind_kph': 6.5, 'wind_degree': 215, 'wind_dir': 'SW', 'pressure_mb': 1017.0, 'pressure_in': 30.02, 'precip_mm': 0.0, 'precip_in': 0.0, 'humidity': 86, 'cloud': 0, 'feelslike_c': 11.3, 'feelslike_f': 52.4, 'windchill_c': 8.7, 'windchill_f': 47.7, 'heatindex_c': 9.8, 'heatindex_f': 49.7, 'dewpoint_c': 9.6, 'dewpoint_f': 49.2, 'vis_km': 16.0, 'vis_miles': 9.0, 'uv': 0.0, 'gust_mph': 6.3, 'gust_kph': 10.2}}", "score": 0.885373, "raw_content": null}, {"title": "Weather in San Francisco in June 2025", "url": "https://world-weather.info/forecast/usa/san_francisco/june-2025/", "content": "Detailed ⚡ San Francisco Weather Forecast for June 2025 - day/night 🌡️ temperatures, precipitations - World-Weather.info. Add the current city. Search. Weather; Archive; Weather Widget °F. World; United States; California; Weather in San Francisco; ... 17 +64° +54° 18 +61° +54° 19", "score": 0.8830044, "raw_content": null}], "response_time": 2.6}
==================================[1m Ai Message [0m==================================

Based on the search results, here's the current weather in San Francisco:
- Temperature: 53.1°F (11.7°C)
- Conditions: Foggy
- Wind: 4.0 mph from the SW
- Humidity: 86%
- Visibility: 9.0 miles

The weather appears to be typical for San Francisco, with morning fog and mild temperatures. The "feels like" temperature is 52.4°F (11.3°C).

我们可以查看LangSmith 追踪，以确保它有效地调用了搜索工具。

流式消息传输

我们已经了解了如何使用.invoke调用智能体以获取最终响应。如果智能体执行多个步骤，这可能需要一些时间。为了显示中间进度，我们可以实时流式传输消息。

for step in agent_executor.stream({"messages": [input_message]}, stream_mode="values"):
    step["messages"][-1].pretty_print()

================================[1m Human Message [0m=================================

Search for the weather in SF
==================================[1m Ai Message [0m==================================

[{'text': "I'll help you search for information about the weather in San Francisco.", 'type': 'text'}, {'id': 'toolu_01DCPnJES53Fcr7YWnZ47kDG', 'input': {'query': 'current weather San Francisco'}, 'name': 'tavily_search', 'type': 'tool_use'}]
Tool Calls:
  tavily_search (toolu_01DCPnJES53Fcr7YWnZ47kDG)
 Call ID: toolu_01DCPnJES53Fcr7YWnZ47kDG
  Args:
    query: current weather San Francisco
=================================[1m Tool Message [0m=================================
Name: tavily_search

{"query": "current weather San Francisco", "follow_up_questions": null, "answer": null, "images": [], "results": [{"title": "Weather in San Francisco", "url": "https://www.weatherapi.com/", "content": "{'location': {'name': 'San Francisco', 'region': 'California', 'country': 'United States of America', 'lat': 37.775, 'lon': -122.4183, 'tz_id': 'America/Los_Angeles', 'localtime_epoch': 1750168506, 'localtime': '2025-06-17 06:55'}, 'current': {'last_updated_epoch': 1750167900, 'last_updated': '2025-06-17 06:45', 'temp_c': 11.7, 'temp_f': 53.1, 'is_day': 1, 'condition': {'text': 'Fog', 'icon': '//cdn.weatherapi.com/weather/64x64/day/248.png', 'code': 1135}, 'wind_mph': 4.0, 'wind_kph': 6.5, 'wind_degree': 215, 'wind_dir': 'SW', 'pressure_mb': 1017.0, 'pressure_in': 30.02, 'precip_mm': 0.0, 'precip_in': 0.0, 'humidity': 86, 'cloud': 0, 'feelslike_c': 11.3, 'feelslike_f': 52.4, 'windchill_c': 8.7, 'windchill_f': 47.7, 'heatindex_c': 9.8, 'heatindex_f': 49.7, 'dewpoint_c': 9.6, 'dewpoint_f': 49.2, 'vis_km': 16.0, 'vis_miles': 9.0, 'uv': 0.0, 'gust_mph': 6.3, 'gust_kph': 10.2}}", "score": 0.9542825, "raw_content": null}, {"title": "Weather in San Francisco in June 2025", "url": "https://world-weather.info/forecast/usa/san_francisco/june-2025/", "content": "Detailed ⚡ San Francisco Weather Forecast for June 2025 - day/night 🌡️ temperatures, precipitations - World-Weather.info. Add the current city. Search. Weather; Archive; Weather Widget °F. World; United States; California; Weather in San Francisco; ... 17 +64° +54° 18 +61° +54° 19", "score": 0.8638634, "raw_content": null}], "response_time": 2.57}
==================================[1m Ai Message [0m==================================

Based on the search results, here's the current weather in San Francisco:
- Temperature: 53.1°F (11.7°C)
- Condition: Foggy
- Wind: 4.0 mph from the Southwest
- Humidity: 86%
- Visibility: 9.0 miles
- Feels like: 52.4°F (11.3°C)

This is quite typical weather for San Francisco, which is known for its fog, especially during the morning hours. The city's proximity to the ocean and unique geographical features often result in mild temperatures and foggy conditions.

流式传输令牌

除了流式传输消息之外，流式传输令牌也很有用。我们可以通过指定stream_mode="messages"来实现这一点。

::: note

下面我们使用message.text()，这需要langchain-core>=0.3.37。

:::

for step, metadata in agent_executor.stream(
    {"messages": [input_message]}, stream_mode="messages"
):
    if metadata["langgraph_node"] == "agent" and (text := step.text()):
        print(text, end="|")

I|'ll help you search for information| about the weather in San Francisco.|Base|d on the search results, here|'s the current weather in| San Francisco:
-| Temperature: 53.1°F (|11.7°C)
-| Condition: Foggy
- Wind:| 4.0 mph from| the Southwest
- Humidity|: 86%|
- Visibility: 9|.0 miles
- Pressure: |30.02 in|Hg

The weather| is characteristic of San Francisco, with| foggy conditions and mild temperatures|. The "feels like" temperature is slightly| lower at 52.4|°F (11.|3°C)| due to the wind chill effect|.|

添加记忆

如前所述，这个智能体是无状态的。这意味着它不会记住之前的交互。为了赋予它记忆功能，我们需要传入一个检查点保存器。传入检查点保存器时，我们还需要在调用智能体时传入一个thread_id（这样它就知道从哪个线程/对话恢复）。

from langgraph.checkpoint.memory import MemorySaver

memory = MemorySaver()

API 参考：MemorySaver

agent_executor = create_react_agent(model, tools, checkpointer=memory)

config = {"configurable": {"thread_id": "abc123"}}

input_message = {"role": "user", "content": "Hi, I'm Bob!"}
for step in agent_executor.stream(
    {"messages": [input_message]}, config, stream_mode="values"
):
    step["messages"][-1].pretty_print()

================================[1m Human Message [0m=================================

Hi, I'm Bob!
==================================[1m Ai Message [0m==================================

Hello Bob! I'm an AI assistant who can help you search for information using specialized search tools. Is there anything specific you'd like to know about or search for? I'm happy to help you find accurate and up-to-date information on various topics.

input_message = {"role": "user", "content": "What's my name?"}
for step in agent_executor.stream(
    {"messages": [input_message]}, config, stream_mode="values"
):
    step["messages"][-1].pretty_print()

================================[1m Human Message [0m=================================

What's my name?
==================================[1m Ai Message [0m==================================

Your name is Bob, as you introduced yourself earlier. I can remember information shared within our conversation without needing to search for it.

示例 LangSmith 追踪

如果你想开始新的对话，你只需更改所使用的thread_id

config = {"configurable": {"thread_id": "xyz123"}}

input_message = {"role": "user", "content": "What's my name?"}
for step in agent_executor.stream(
    {"messages": [input_message]}, config, stream_mode="values"
):
    step["messages"][-1].pretty_print()

================================[1m Human Message [0m=================================

What's my name?
==================================[1m Ai Message [0m==================================

I apologize, but I don't have access to any tools that would tell me your name. I can only assist you with searching for publicly available information using the tavily_search function. I don't have access to personal information about users. If you'd like to tell me your name, I'll be happy to address you by it.

总结

总结！在本快速入门指南中，我们介绍了如何创建一个简单的智能体。我们还展示了如何流式传输响应——不仅包括中间步骤，还包括令牌！我们还添加了记忆功能，以便你可以与它们进行对话。智能体是一个复杂的话题，有很多东西需要学习！

有关智能体的更多信息，请查阅LangGraph文档。该文档包含其自身的一系列概念、教程和操作指南。

端到端智能体​

设置​

Jupyter Notebook​

安装​

LangSmith​

Tavily​

定义工具​

使用语言模型​

创建智能体​

运行智能体​

流式消息传输​

流式传输令牌​

添加记忆​

总结​