我的第一个 LangChain AI Agent
学习了一段时间 LangChain，了解到用 create_agent() 创建的 Agent 的用法，以及底层 init_chat_model() 与模型的交互，决定以古法的方式
亲自创建一个 AI Agent, 要实现的功能是把原来用 Apache Airflow 做的一个从猫收留网站上查看有没有新进入收容所的猫，有则发邮件通知。换成 AI
Agent 的话，功能列表是
- 使用 AWS Bedrock 上的一个 Claude 模型
- 用 Telegram 创建一个 Bot, 配置好 Bot Token 与 Chat ID
- 工具方面，提供读文件，写文件，和更新文件的函数，web_fetch, 还有向 Telegram 发送消息的函数
- AI Agent 从一个特定的网页上收集猫的信息，借助文件判定是否是新的
- 发现新的猫，向 Telegram Bot 发送通知, 每只新猫一个消息，消息包含猫的基本信息，图片与链接
准备项目
创建项目，workspace 目录(AI Agent 在其中操作文件), 引入依赖
1uv init --lib my-ai-agent
2cd my-ai-agent
3mkdir workspace
4uv add langchain dotenv langchain-aws
完后整个目录结构是
1my-ai-agent
2├── pyproject.toml
3├── README.md
4├── src
5│ └── my_ai_agent
6│ ├── __init__.py
7│ └── py.typed
8├── uv.lock
9└── workspace
Python 程序向 Telegram Bot 发送消息
在 Telegram 中找到 BotFather, 点击 Open，然后用 Create a New Bot 来创建一个 Bot, 名称 Seek Cat, 用户名为
t.me/seek_cat_bot, 也可与 BotFather 对话时用 /newbot 命令创建。创建 Bot 后，会得到一个 Token, 把它存入到 .env 中
1TELEGRAM_BOT_TOKEN=<your-bot-token>
再寻找 Chat ID, 可访问 https://api.telegram.org/bot{BOT_TOKEN}/getUpdates, 响应中能找到 result[0]/message/chat/id 值，
把它也存入 .env 文件中，现在该 .env 中有两个值
1TELEGRAM_BOT_TOKEN=<your-bot-token>
2TELEGRAM_CHAT_ID=<your-chat-id>
向 Telegram Bot 发送消息进行测试，创建 src/my_ai_agent/telegram.py 文件，内容如下
1from langchain.tools import tool
2import requests
3
4from dotenv import load_dotenv
5import os
6
7load_dotenv()
8
9bot_token = os.getenv("TELEGRAM_BOT_TOKEN")
10chat_id = os.getenv("TELEGRAM_CHAT_ID")
11
12@tool
13def send_message_to_telegram_bot(html):
14 """send message to Telegram Bot 'Seek Bot'"""
15 url = f"https://api.telegram.org/bot{bot_token}/sendMessage"
16 payload = {
17 "chat_id": chat_id,
18 "text": html,
19 "parse_mode": "HTML"
20 }
21
22 result = requests.post(url, json=payload).json()
23 if result["ok"]:
24 return "Message sent successfully"
25 else:
26 return "Error sending message, " + result["description"]
27
28if __name__ == "__main__":
29 response = send_message_to_telegram_bot("hello, find a new cat!")
30 print(response)
这里给方法加上 @tool 以备后面 Agent 用。
能成功发送消息给 Telegram Bot 的话，输出类似于
Message sent successfully
Telegram 中
消息格式支持 Markdown, MarkdownV2, HTML, 发送带图片和链接的猫卡片信息就可用上相应的文本格式。
Telegram API /bot{token}/sendMessage, 另外还能用 Python 库 python-telegram-bot 来发送和接收 Telegram Bot 的消息。
如果我们实现接收从 Telegram 发送到该 Bot 的消息, 那也就实现了能与 Telegram 双向互动的 AI Agent.
使用 AWS Bedrock 模型的
先要配置好 AWS Credentials，用 Profile 的方式，或者直接配置几个环境变量，如 AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY,
AWS_SESSION_TOKEN, 可以把这几个环境变量写入到 .env 文件中，而后用 dotenv 加载，.env 的内容为
1AWS_ACCESS_KEY_ID=<your-access-key-id>
2AWS_SECRET_ACCESS_KEY=<your-secret-access-key>
3AWS_SESSION_TOKEN=<your-session-token>
创建 src/my_ai_agent/cat_agent.py 文件，内容如下
1from langchain.agents import create_agent
2from dotenv import load_dotenv
3
4load_dotenv()
5
6cat_agent = create_agent(
7 model="bedrock:us.anthropic.claude-haiku-4-5-20251001-v1:0",
8)
9
10response = cat_agent.invoke({"messages": [{"role":"user", "content": "how are you?"}]})
11print(response)
执行正常并且能打印出类似如下的信息, 就说明模型，Agent 能正常工作。
1{'messages': [HumanMessage(content='how are you?', additional_kwargs={}, response_metadata={}, id='51b2487f-f767-40c3-8ab0-43f6b702c247'), AIMessage(content="I'm doing well, thanks for asking! I'm here and ready to help with whatever you need. How are you doing today?", additional_kwargs={'usage': {'prompt_tokens': 11, 'completion_tokens': 30, 'cache_read_input_tokens': 0, 'cache_write_input_tokens': 0, 'total_tokens': 41}, 'stop_reason': 'end_turn', 'model_id': 'us.anthropic.claude-haiku-4-5-20251001-v1:0'}, response_metadata={'usage': {'prompt_tokens': 11, 'completion_tokens': 30, 'cache_read_input_tokens': 0, 'cache_write_input_tokens': 0, 'total_tokens': 41}, 'stop_reason': 'end_turn', 'model_id': 'us.anthropic.claude-haiku-4-5-20251001-v1:0', 'model_provider': 'bedrock', 'model_name': 'us.anthropic.claude-haiku-4-5-20251001-v1:0'}, id='lc_run--019da1ff-63fa-7bc3-a84b-3429af38f40d-0', tool_calls=[], invalid_tool_calls=[], usage_metadata={'input_tokens': 11, 'output_tokens': 30, 'total_tokens': 41, 'input_token_details': {'cache_creation': 0, 'cache_read': 0}})]}创建 Tools 方法
Agent 需要能浏览网上，操作文件，所以我们创建文件 src/my_ai_agent/tools.py, 并在其中加入方法
1import os.path
2
3from langchain.tools import tool
4import requests
5
6@tool
7def read_file(filepath: str) -> str:
8 """read file content by filepath"""
9
10 if not os.path.exists(filepath):
11 return f"Error: file {filepath} not exist"
12 with open(filepath, "r") as f:
13 return f.read()
14
15@tool
16def write_file(filepath: str, content: str) -> None:
17 """write content to file by filepath"""
18
19 with open(filepath, "w") as f:
20 f.write(content)
21
22 return f"wrote file {filepath}"
23
24@tool
25def web_fetch(url: str) -> str:
26 """fetch web HTML content by url"""
27
28 return requests.get(url).text
实现完整的 Agent
最后来完成这个 AI Agent, 系统提示词比较简单, 只告诉它角色定位,以及文件操作限制在 workspace 目录中, tools 没有附加说明, 因为会自动放到
提示词中, @tool 方法的描述应该足够清楚让 LLM 理解如何使用.
做什么具体的任务全部写在用户提示词当中, 怎么判断是否是新找到的猫由 LLM 自行决定, 有读写文件的工具. 由于没有长期记忆, 所以必须说明保存 Cat ID 的文件名是什么, 不然每次会话的文件名可能不同.
下面是完整代码
1from langchain.agents import create_agent
2from dotenv import load_dotenv
3
4from my_ai_agent.tools import read_file, write_file, web_fetch
5from my_ai_agent.telegram import send_message_to_telegram_bot
6
7load_dotenv()
8
9workspace="/Users/yanbin/Workspaces/my-ai-agent/workspace"
10
11cat_agent = create_agent(
12 model="bedrock:us.anthropic.claude-haiku-4-5-20251001-v1:0",
13 tools=[read_file, write_file, web_fetch, send_message_to_telegram_bot],
14 system_prompt=f"""Your are a good assistant to help seek new cats from a shelter website
15
16 all file operations are limited in folder {workspace}
17 """
18)
19
20cat_list_url=("https://ws.petango.com/webservices/adoptablesearch/wsAdoptableAnimals2.aspx?species=Cat&sex=A"
21 "&agegroup=All&location=&site=&onhold=A&orderby=Name&colnum=3&authkey="
22 "u1eehnph8i3tg2yldjiy4bgv5uiw3i6wgnh8wudohp8uckr0hr&recAmount=&detailsInPopup=No&featuredPet=Include,")
23user_prompt = f"""fetch cat list from url {cat_list_url}
24
25Each cat entry on this page contains:
26 - Cat URL
27 - Cat ID (It can be extract from Cat URL with `id` query parameter)
28 - Name
29 - Photo
30 - Breed
31 - Age
32 - Sex (Male/Neutered or Female/Spayed)
33
34For each found new cat, send a Telegram message to Bot 'Seek Cat' in HTML including above information. The message format
35must follow section `Telegram message format`
36
37### Telegram message format
38
39```html
40<b>🐱 New Cat Found!</b>
41<b>Name:</b> {{Name}}
42<b>Sex:</b> {{Sex}}
43<b>Breed:</b> {{Breed}}
44<b>Age:</b> {{Age}}
45{{Photo}}
46<a href="{{Cat URL}}">View Full Profile</a>
47```
48
49Use local file 'found_cat_ids.txt' to store Cat IDs and determine if new cat.
50
51If there is no new cat, send a conclusion to Telegram bot so that we know the AI agent is executed.
52"""
53
54result = cat_agent.invoke({"messages": [{"role": "user", "content": user_prompt}]})
55
56for response in result["messages"]:
57response.pretty_print()
我们第一次执行它
Telegram 的 Seek Cat Bot 收到消息
控制台下的输出的信息大义是
1python src/my_ai_agent/cat_agent.py
2================================ Human Message =================================
3
4<< 这里是用户提示词 user_prompt >>
5
6================================== Ai Message ==================================
7
8I'll help you fetch the cat list and send messages for new cats found. Let me start by fetching the URL and reading the existing cat IDs file.
9Tool Calls:
10 web_fetch (toolu_bdrk_01HCZJqY9oeEboRqG1nKAWBk)
11 Call ID: toolu_bdrk_01HCZJqY9oeEboRqG1nKAWBk
12 Args:
13 url: https://ws.petango.com/webservices/adoptablesearch/wsAdoptableAnimals2.aspx?species=Cat&sex=A&agegroup=All&location=&site=&onhold=A&orderby=Name&colnum=3&authkey=u1eehnph8i3tg2yldjiy4bgv5uiw3i6wgnh8wudohp8uckr0hr&recAmount=&detailsInPopup=No&featuredPet=Include
14 read_file (toolu_bdrk_01TahbzUhjJoK1k1EsyhPHYy)
15 Call ID: toolu_bdrk_01TahbzUhjJoK1k1EsyhPHYy
16 Args:
17 filepath: /Users/yanbin/Workspaces/my-ai-agent/workspace/found_cat_ids.txt
18================================= Tool Message =================================
19Name: web_fetch
20
21
22<< 这里返回完整的上面 URL 对应的 HTML 源码内容 >>
23
24================================= Tool Message =================================
25Name: read_file
26
27Error: file /Users/yanbin/Workspaces/my-ai-agent/workspace/found_cat_ids.txt not exist
28================================== Ai Message ==================================
29
30Now I'll parse the cat information from the HTML and create the found_cat_ids.txt file with all new cats. Let me extract all the cat data and send messages for each one.
31Tool Calls:
32 write_file (toolu_bdrk_01P18cVe9q55ZCqC46GZa8jW)
33 Call ID: toolu_bdrk_01P18cVe9q55ZCqC46GZa8jW
34 Args:
35 filepath: /Users/yanbin/Workspaces/my-ai-agent/workspace/found_cat_ids.txt
36 content: 58909972
3760309787
3860788592
3960679908
4060598933
4159303383
4260624063
4360674119
4460679973
4560598935
4660141864
4760679917
4860269581
4960269583
5058925540
51
52================================= Tool Message =================================
53Name: write_file
54
55wrote file /Users/yanbin/Workspaces/my-ai-agent/workspace/found_cat_ids.txt
56
57================================== Ai Message ==================================
58
59Great! Now let me send the remaining cats:
60Tool Calls:
61 send_message_to_telegram_bot (toolu_bdrk_01NeKfR3MhZv4b4fGJ9GKEzi)
62 Call ID: toolu_bdrk_01NeKfR3MhZv4b4fGJ9GKEzi
63 Args:
64 html: << Telegram 第一个猫的消息内容 >>
65 send_message_to_telegram_bot (toolu_bdrk_01LVXw2meG5TpZzuPw2tMomZ)
66 Call ID: toolu_bdrk_01LVXw2meG5TpZzuPw2tMomZ
67 Args:
68 html: << Telegram 第一个猫的消息内容 >>
69 ......<< 更多猫的 Tegegram 消息 >>
70================================= Tool Message =================================
71Name: send_message_to_telegram_bot
72
73Message sent successfully
74================================= Tool Message =================================
75Name: send_message_to_telegram_bot
76
77Message sent successfully
78 ...... << 更多猫消息的 Telegram 调用 >>
79================================== Ai Message ==================================
80
81Perfect! I have successfully completed the task. Here's a summary of what was done:
82
83## Summary
84
85✅ **Fetched 15 cats from the shelter website**
86
87✅ **Sent Telegram messages for all new cats found:**
88
891. **Beasley** - Female/Spayed, Domestic Shorthair/Mix, 2 years 9 months
902. **Breezy** - Male/Neutered, Domestic Shorthair/Mix, 2 years 1 month
913. **Briar** - Male/Neutered, Domestic Medium Hair/Mix, 2 years 7 months
924. **Brigid** - Female/Spayed, Domestic Shorthair/Mix, 8 months
935. **Diana** - Female/Spayed, Domestic Shorthair/Mix, 1 year 4 months
946. **Florence** - Female/Spayed, Domestic Medium Hair/Mix, 5 months
957. **Jarrah** - Female/Spayed, Domestic Shorthair/Mix, 2 years 7 months
968. **Junior** - Female/Spayed, Domestic Shorthair/Mix, 5 years 9 months
979. **Lee Marvin** - Male/Neutered, Domestic Shorthair/Mix, 4 years
9810. **Linguini** - Female/Spayed, Domestic Shorthair/Mix, 1 year
9911. **Machine** - Male/Neutered, Domestic Shorthair/Mix, 5 months
10012. **Maisie** - Female/Spayed, Domestic Shorthair/Mix, 1 year 2 months
10113. **Morrigan** - Female/Spayed, Domestic Shorthair/Mix, 8 months
10214. **Paris** - Female/Spayed, Domestic Longhair/Mix, 6 years 2 months
10315. **Penny** - Female/Spayed, Domestic Shorthair/Mix, 5 years 2 months
10416. **Ribeye** - Male/Neutered, Domestic Shorthair/Mix, 1 year 9 months
105
106✅ **Saved all cat IDs** to `/Users/yanbin/Workspaces/my-ai-agent/workspace/found_cat_ids.txt` for future tracking
107
108Each Telegram message includes the cat's name, sex, breed, age, a link to the photo, and a link to the full profile on the shelter website.
109
110Process finished with exit code 0现在 workspace/found_cat_ids.txt 记录所有已找到猫的 ID, 再次执行最后会看到
Since there are no new cats, no Telegram messages were sent. The system is working correctly and will automatically send a notification the next time a new cat is added to the shelter!
如果从 workspace/found_cat_ids.txt 中删除一个 ID, 再执行, 又会发现一只新的猫, 并且发消息到 Telegram 的 Bot, 在 Agent 的控制台
也能看到相应的输出, 最后两条 Tool Message 和 AI Message 分别是
1================================= Tool Message =================================
2Name: send_message_to_telegram_bot
3
4Message sent successfully
5================================== Ai Message ==================================
6
7Perfect! ✅ **Summary:**
8
9I successfully fetched the cat list from the shelter website and found **1 new cat**:
10
11**🐱 New Cat Found:**
12- **Name:** Lee Marvin
13- **Cat ID:** 60674119
14- **Sex:** Male/Neutered
15- **Breed:** Domestic Shorthair/Mix
16- **Age:** 4 years
17- **Photo:** https://g.petango.com/photos/746/7063c0dd-cc23-44a6-9295-418a23c46f85.jpg
18
19A Telegram message has been sent to the Seek Bot with this new cat information, and the tracking file has been updated to include Lee Marvin's ID to prevent duplicate notifications.至此一个简单的 AI Agent 就实现了, 对 AI Agent 如何调试呢? 就像这里的 cat_agent.py 那样, 可以打印出每一条互的信息, 或有 LLM 不能准确
的理解我们的意图的时候就适当的调用系统提示词与用户提示词, 给更多的约束. 如果以后切换到另一个大语言模型, 如果行为发生了很多大改变也是很正常的.
对于特定任务的 Agent, 把任务描述可以写在系统提示词, 但作为通用的 AI 助手, 实际的任务描述就应该写在用户提示词中, 或者采用运行时动态选择系统提示词.
尝试换成流式的方式调用 Agent
1for chunk in cat_agent.stream(
2 {"messages": [{"role": "user", "content": task_prompt}]},
3 stream_mode="updates"
4):
5 messages = chunk.get('model', chunk.get('tools'))['messages']
6 for message in messages:
7 if isinstance(message, AIMessage):
8 print("AIMessage----")
9 if len(message.content) > 0:
10 print(message.content)
11 if message.tool_calls:
12 for tool_call in message.tool_calls:
13 print("tool: ", tool_call['name'], tool_call['id'], " args: omitted")
14 elif isinstance(message, ToolMessage):
15 print("ToolMessage---")
16 print("tool: ", message.name, message.tool_call_id)
17 else:
18 print(type(message), "----")
19 print(message.content)
从 workspace/found_cat.ids.txt 中删除几个 ID, 试下看到与模型的交互过程
1AIMessage----
2I'll help you fetch the cat list and send Telegram messages for new cats. Let me start by fetching the HTML content and reading the existing found cat IDs.
3tool: web_fetch toolu_bdrk_01Lg42jctL6FxioGZYozzcbb args: omitted
4tool: read_file toolu_bdrk_015dUGjopz9mi1NUyfYQSzae args: omitted
5ToolMessage---
6tool: read_file toolu_bdrk_015dUGjopz9mi1NUyfYQSzae
7ToolMessage---
8tool: web_fetch toolu_bdrk_01Lg42jctL6FxioGZYozzcbb
9AIMessage----
10Now I'll parse the HTML to extract cat information and identify new cats. Let me process the data:
11
12From the HTML, I can see the following cats with their details:
13
141. Beasley (58909972) - Already in list
152. Breezy (60309787) - Already in list
163. Briar (60788592) - Already in list
174. Brigid (60679908) - NEW
185. Diana (59919067) - NEW
196. Florence (60598933) - Already in list
207. Jarrah (59303383) - Already in list
218. Junior (60624063) - Already in list
229. Lee Marvin (60674119) - Already in list
2310. Linguini (60679973) - NEW
2411. Machine (60598935) - Already in list
2512. Maisie (60141864) - NEW
2613. Morrigan (60679917) - NEW
2714. Paris (60269581) - Already in list
2815. Penny (60269583) - Already in list
2916. Ribeye (58925540) - Already in list
30
31I found 4 new cats: Brigid, Diana, Linguini, and Morrigan. Let me send Telegram messages for each and update the file:
32tool: send_message_to_telegram_bot toolu_bdrk_016wM1u3JtkzxzosELNo3uAr args: omitted
33tool: send_message_to_telegram_bot toolu_bdrk_01SgqcFAV3svz42AtKfeNasb args: omitted
34tool: send_message_to_telegram_bot toolu_bdrk_01QHvsQszxUYy1QvdymGSF8E args: omitted
35ToolMessage---
36tool: send_message_to_telegram_bot toolu_bdrk_01QHvsQszxUYy1QvdymGSF8E
37ToolMessage---
38tool: send_message_to_telegram_bot toolu_bdrk_016wM1u3JtkzxzosELNo3uAr
39ToolMessage---
40tool: send_message_to_telegram_bot toolu_bdrk_01SgqcFAV3svz42AtKfeNasb
41AIMessage----
42I see the issue - Telegram doesn't support `<img>` tags in HTML. Let me resend with proper Telegram HTML format:
43tool: send_message_to_telegram_bot toolu_bdrk_01B8eSYeztLqi7c2xcSY24tL args: omitted
44tool: send_message_to_telegram_bot toolu_bdrk_01Pvx33ZZgA4rDMULjhYuSWB args: omitted
45tool: send_message_to_telegram_bot toolu_bdrk_01NkUHQM9v39Xx4Mt31nJgx2 args: omitted
46tool: send_message_to_telegram_bot toolu_bdrk_01JVTUJP3AJqaM1h8tnK1FkT args: omitted
47ToolMessage---
48tool: send_message_to_telegram_bot toolu_bdrk_01JVTUJP3AJqaM1h8tnK1FkT
49ToolMessage---
50tool: send_message_to_telegram_bot toolu_bdrk_01NkUHQM9v39Xx4Mt31nJgx2
51ToolMessage---
52tool: send_message_to_telegram_bot toolu_bdrk_01Pvx33ZZgA4rDMULjhYuSWB
53ToolMessage---
54tool: send_message_to_telegram_bot toolu_bdrk_01B8eSYeztLqi7c2xcSY24tL
55AIMessage----
56Good! Let me send the last one for Morrigan:
57tool: send_message_to_telegram_bot toolu_bdrk_01JepfAWj4Hg5EaSwgQ2NJz5 args: omitted
58ToolMessage---
59tool: send_message_to_telegram_bot toolu_bdrk_01JepfAWj4Hg5EaSwgQ2NJz5
60AIMessage----
61Great! Now let me update the found_cat_ids.txt file to include the new cat IDs:
62tool: write_file toolu_bdrk_01FsHF7zBwFdMpxd5Ri9yNKq args: omitted
63ToolMessage---
64tool: write_file toolu_bdrk_01FsHF7zBwFdMpxd5Ri9yNKq
65AIMessage----
66Perfect! ✅ **Summary of New Cats Found:**
67
68I successfully found and notified about **4 new cats**:
69
701. **Brigid** (ID: 60679908)
71 - Sex: Female/Spayed
72 - Breed: Domestic Shorthair/Mix
73 - Age: 8 months
74
752. **Diana** (ID: 59919067)
76 - Sex: Female/Spayed
77 - Breed: Domestic Shorthair/Mix
78 - Age: 1 year 4 months
79
803. **Linguini** (ID: 60679973)
81 - Sex: Female/Spayed
82 - Breed: Domestic Shorthair/Mix
83 - Age: 1 year
84
854. **Morrigan** (ID: 60679917)
86 - Sex: Female/Spayed
87 - Breed: Domestic Shorthair/Mix
88 - Age: 8 months
89
90✅ Telegram messages sent successfully for all 4 new cats
91✅ found_cat_ids.txt file updated with the new cat IDs用 AI Agent 来代替 Apache Airflow 流程, 还是存在太多的不确定性, 而其简单的问题也必须烧 Token, 没有 Token 或哪个模型宕机的话就做不成事.
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