feat: add ReAct agent with custom API support
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## 课程大纲
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### ✅ 第 1 步：核心理念
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- LangGraph 是基于图的 AI 应用框架
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- 支持有状态、循环、分支的智能体构建
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| 步骤 | 内容 | 文件 | 状态 |
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|------|------|------|------|
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| 第 1 步 | 核心理念 | - | ✅ |
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| 第 2 步 | Hello World | `hello.py` | ✅ |
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| 第 3 步 | 条件边 | `conditional.py` | ✅ |
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| 第 4 步 | 循环 + 智能体 | `loop.py`, `agent.py` | ✅ |
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| 第 5 步 | ReAct 智能体 | `react_agent.py` | ✅ |
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### ✅ 第 2 步：Hello World
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- 文件: `hello.py`
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- 学习了：State、Node、Edge 三大核心概念
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### ✅ 第 3 步：条件边
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- 文件: `conditional.py`
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- 学习了：让图学会做决定，根据输入走不同路径
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### ✅ 第 4 步：循环 + 智能体
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- 文件: `loop.py` - 循环演示（尝试-评估-重试）
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- 文件: `agent.py` - AI 智能体（思考-行动-回答）
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## 核心概念总结
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## 核心概念
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```
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LangGraph 图 = State(状态) + Node(节点) + Edge(边)
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@ -30,22 +22,9 @@ Edge: 连接节点，定义流程走向
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- 条件边: add_conditional_edges()
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```
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## 下一步学习
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### 第 5 步：真实 LLM 智能体
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- 接入 OpenAI API
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- 构建 ReAct 模式智能体
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- 添加工具调用能力
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### 第 6 步：高级特性
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- 检查点机制（暂停/恢复）
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- 子图（嵌套图）
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- 并行执行
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- 流式输出
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## 运行示例
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```bash
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```powershell
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# 设置编码
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$env:PYTHONIOENCODING="utf-8"
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@ -53,15 +32,28 @@ $env:PYTHONIOENCODING="utf-8"
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python hello.py # Hello World
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python conditional.py # 条件边
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python loop.py # 循环
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python agent.py # AI 智能体
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python agent.py # AI 智能体 (模拟模式)
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python react_agent.py # ReAct 智能体 (需要 API)
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```
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## 接入真实 LLM
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## ReAct 智能体配置
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```powershell
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# 设置 API Key
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$env:OPENAI_API_KEY = "sk-..."
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# 必需
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$env:OPENAI_API_KEY = "your-api-key"
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# 运行智能体示例
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python agent.py
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# 可选
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$env:OPENAI_BASE_URL = "https://your-api.com/v1" # 默认 OpenAI
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$env:MODEL_NAME = "gpt-4o-mini" # 默认 gpt-4o-mini
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# 运行
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python react_agent.py # 内置测试
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python react_agent.py "你的问题" # 自定义问题
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```
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## 下一步学习
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- [ ] 检查点机制（暂停/恢复）
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- [ ] 子图（嵌套图）
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- [ ] 并行执行
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- [ ] 流式输出
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227
langgraph-tutorial/react_agent.py
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227
langgraph-tutorial/react_agent.py
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"""
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LangGraph 第 5 步：真实 LLM 智能体
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ReAct 模式：思考(Reason) - 行动(Act) - 观察(Observe)
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支持自定义 OpenAI 兼容 API
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"""
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import os
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import sys
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from langgraph.graph import StateGraph, START, END
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from typing import TypedDict
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# 1️⃣ 配置 API
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API_KEY = os.environ.get("OPENAI_API_KEY", "")
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BASE_URL = os.environ.get("OPENAI_BASE_URL", "https://api.openai.com/v1")
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MODEL = os.environ.get("MODEL_NAME", "gpt-4o-mini")
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if not API_KEY:
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print("请先设置环境变量:")
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print(" $env:OPENAI_API_KEY = 'your-api-key'")
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print(" $env:OPENAI_BASE_URL = 'your-api-base-url' # 可选，默认 OpenAI")
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print(" $env:MODEL_NAME = 'gpt-4o-mini' # 可选")
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exit(1)
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from openai import OpenAI
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client = OpenAI(api_key=API_KEY, base_url=BASE_URL)
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# 2️⃣ 定义状态
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class AgentState(TypedDict):
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question: str
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thoughts: list
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current_thought: str
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action: str
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action_param: str
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observation: str
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final_answer: str
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iteration: int
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max_iterations: int
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# 3️⃣ 定义工具
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def calculator(expression: str) -> str:
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"""计算器工具"""
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try:
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result = eval(expression, {"__builtins__": {}}, {})
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return f"计算结果: {expression} = {result}"
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except Exception as e:
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return f"计算错误: {e}"
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def search_knowledge(query: str) -> str:
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"""知识库搜索工具"""
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knowledge = {
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"langgraph": "LangGraph 是 LangChain 团队开发的框架，用于构建有状态、基于图的 AI 应用。",
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"python": "Python 是一种高级编程语言，广泛用于 AI、Web 开发、数据分析等领域。",
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"langchain": "LangChain 是构建 LLM 应用的框架，提供 Prompt 管理、Chain、Agent 等组件。",
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"ai": "人工智能 (AI) 是计算机科学的一个分支，致力于创建能执行智能任务的系统。",
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}
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for key, value in knowledge.items():
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if key in query.lower():
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return f"搜索到: {value}"
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return f"未找到关于 '{query}' 的精确信息"
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tools = {
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"calculator": calculator,
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"search": search_knowledge,
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}
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# 4️⃣ 定义节点
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def think_node(state: AgentState):
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"""思考节点 - 让 LLM 决定下一步"""
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state = state.copy()
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state['iteration'] += 1
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system_prompt = f"""你是一个智能助手，可以使用以下工具:
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1. calculator - 数学计算，参数是数学表达式如 "2+3*4"
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2. search - 搜索知识，参数是搜索关键词
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当前是第 {state['iteration']}/{state['max_iterations']} 轮。
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请严格按照以下格式回复:
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[思考] 你的思考过程
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[行动] 工具名称|参数
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例如:
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[思考] 我需要计算这个数学题
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[行动] calculator|2+3*4
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如果可以直接回答，请这样回复:
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[思考] 我已经知道答案了
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[回答] 你的最终答案"""
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messages = [{"role": "system", "content": system_prompt}]
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messages.append({"role": "user", "content": state['question']})
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if state.get('observation'):
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messages.append({"role": "assistant", "content": f"[观察] {state['observation']}"})
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response = client.chat.completions.create(
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model=MODEL,
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messages=messages,
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max_tokens=300,
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temperature=0.3,
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)
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thought_text = response.choices[0].message.content
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state['current_thought'] = thought_text
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state['thoughts'] = state.get('thoughts', []) + [thought_text]
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print(f"\n{'='*50}")
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print(f"[思考] 第 {state['iteration']} 轮:")
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print(thought_text)
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# 解析行动
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for line in thought_text.split('\n'):
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if '[行动]' in line:
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parts = line.replace('[行动]', '').strip().split('|')
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if len(parts) == 2:
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state['action'] = parts[0].strip()
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state['action_param'] = parts[1].strip()
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return state
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if '[回答]' in line:
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state['final_answer'] = line.replace('[回答]', '').strip()
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return state
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state['action'] = ""
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return state
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def act_node(state: AgentState):
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"""行动节点 - 执行工具"""
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state = state.copy()
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action = state.get('action', '')
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param = state.get('action_param', '')
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print(f"\n[行动] 执行 {action}({param})")
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if action in tools:
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result = tools[action](param)
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state['observation'] = result
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print(f"[观察] {result}")
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else:
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state['observation'] = f"未知工具: {action}"
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print(f"[观察] 未知工具: {action}")
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return state
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def answer_node(state: AgentState):
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"""回答节点 - 生成最终答案"""
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state = state.copy()
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if state.get('final_answer'):
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print(f"\n[回答] {state['final_answer']}")
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return state
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messages = [
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{"role": "system", "content": "请根据以下信息给出简洁的最终答案"},
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{"role": "user", "content": f"问题: {state['question']}\n\n思考过程:\n" + "\n".join(state.get('thoughts', []))}
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]
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response = client.chat.completions.create(
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model=MODEL,
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messages=messages,
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max_tokens=200,
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)
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state['final_answer'] = response.choices[0].message.content
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print(f"\n[回答] {state['final_answer']}")
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return state
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# 5️⃣ 路由函数
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def route(state: AgentState):
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"""决定下一步"""
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if state.get('final_answer'):
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return "answer"
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if state['iteration'] >= state['max_iterations']:
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return "answer"
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if state.get('action'):
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return "act"
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return "answer"
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# 6️⃣ 构建图
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graph = StateGraph(AgentState)
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graph.add_node("think", think_node)
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graph.add_node("act", act_node)
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graph.add_node("answer", answer_node)
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graph.add_edge(START, "think")
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graph.add_conditional_edges("think", route, {"act": "act", "answer": "answer"})
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graph.add_edge("act", "think")
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graph.add_edge("answer", END)
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app = graph.compile()
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# 7️⃣ 运行
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print("=" * 50)
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print("LangGraph ReAct 智能体")
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print("=" * 50)
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print(f"API: {BASE_URL}")
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print(f"模型: {MODEL}")
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print("\n图结构:")
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print(" START -> think -> [有行动?] -> act -> think (循环)")
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print(" |")
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print(" +-> [无行动/达到限制] -> answer -> END")
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# 如果有命令行参数，用命令行参数作为问题
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if len(sys.argv) > 1:
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questions = [" ".join(sys.argv[1:])]
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else:
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questions = [
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"计算一下 123 * 456",
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"什么是 LangGraph？",
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]
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for q in questions:
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print(f"\n{'#'*50}")
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print(f"问题: {q}")
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print(f"{'#'*50}")
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result = app.invoke({
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"question": q,
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"thoughts": [],
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"iteration": 0,
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"max_iterations": 4,
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"action": "",
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"observation": "",
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"final_answer": "",
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"action_param": "",
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})
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print(f"\n{'='*50}")
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print(f"最终答案: {result['final_answer']}")
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print(f"{'='*50}")
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