add langgraph use

examples/stream_modes/updates_demo.py

@@ -0,0 +1,75 @@
+from typing import TypedDict, Annotated
+import operator
+import time
+
+from langgraph.graph import StateGraph, END
+
+
+class GraphState(TypedDict):
+    messages: Annotated[list, operator.add]
+    step_count: int
+    result: str
+
+
+def step_1(state: GraphState) -> GraphState:
+    time.sleep(0.3)
+    return {
+        "messages": ["步骤1: 开始数据准备"],
+        "step_count": state.get("step_count", 0) + 1,
+        "result": "数据准备完成",
+    }
+
+
+def step_2(state: GraphState) -> GraphState:
+    time.sleep(0.4)
+    return {
+        "messages": ["步骤2: 正在处理数据"],
+        "step_count": state.get("step_count", 0) + 1,
+        "result": "数据处理完成，准备分析",
+    }
+
+
+def step_3(state: GraphState) -> GraphState:
+    time.sleep(0.5)
+    total_messages = len(state.get("messages", []))
+    return {
+        "messages": ["步骤3: 分析完成，生成最终结果"],
+        "step_count": state.get("step_count", 0) + 1,
+        "result": f"分析完成！共 {total_messages + 1} 条消息，步骤 {state.get('step_count', 0) + 1}",
+    }
+
+
+def create_workflow():
+    wf = StateGraph(GraphState)
+    wf.add_node("step_1", step_1)
+    wf.add_node("step_2", step_2)
+    wf.add_node("step_3", step_3)
+    wf.set_entry_point("step_1")
+    wf.add_edge("step_1", "step_2")
+    wf.add_edge("step_2", "step_3")
+    wf.add_edge("step_3", END)
+    return wf.compile()
+
+
+def main():
+    print("=" * 60)
+    print("🔄 LangGraph stream_mode='updates' 示例（仅返回增量）")
+    print("=" * 60)
+
+    app = create_workflow()
+    initial = {"messages": [], "step_count": 0, "result": ""}
+
+    # 自行维护完整状态
+    current_state = dict(initial)
+    for chunk in app.stream(initial, stream_mode="updates"):
+        for node_name, updates in chunk.items():
+            print(f"📦 {node_name} 更新: {updates}")
+            current_state.update(updates)
+
+    print("\n✅ 最终合并状态:")
+    print(current_state)
+
+
+if __name__ == "__main__":
+    main()
+