LangGraph(Python)中Chatbot节点多余条件边的成因及解决方法

我是LangGraph（Python）的新手，正在学习LangGraph官方文档中的对话历史总结示例。我的代码如下：

class State(TypedDict):
    summary: str
    messages: list

def summarize_conversation(state: State):
    # First, we summarize the conversation
    summary = state.get("summary", "")
    if summary:
        # If a summary already exists, we use a different system prompt
        # to summarize it than if one didn't
        summary_message = (
            f"This is summary of the conversation to date: {summary}\n\n"
            "Extend the summary by taking into account the new messages above:"
        )
    else:
        summary_message = "Create a summary of the conversation above:"

    messages = state["messages"] + [HumanMessage(content=summary_message)]
    response = model.invoke(messages)
    return {"summary": response.content, "messages": messages}

graph_builder = StateGraph(State)
graph_builder.add_node("tools", ToolNode(tool_set))
graph_builder.add_node("chatbot", lambda state: {"messages":assistant_runnable.invoke(state)})
graph_builder.add_node("summarize_conversation", summarize_conversation)
graph_builder.add_edge("tools", "summarize_conversation")
graph_builder.add_edge("summarize_conversation", "chatbot")
graph_builder.add_conditional_edges(
    "chatbot", tools_condition
)
graph_builder.set_entry_point("chatbot")
graph = graph_builder.compile()

问题在于，Chatbot节点到summarize_conversation节点出现了一条多余的条件边：

注：为简洁起见，未附上完整代码。

问题成因 #

这条多余的条件边是由tools_condition函数的逻辑错误导致的：

• 调用add_conditional_edges("chatbot", tools_condition)时，LangGraph会根据tools_condition函数的返回值创建对应跳转边。
• 如果tools_condition在某些场景下返回了summarize_conversation节点名称，就会自动生成Chatbot到该节点的条件边。

解决方法 #

1. 修正tools_condition函数逻辑
   确保该函数仅返回预定义节点名（比如"tools"）或END（表示流程结束），不要返回summarize_conversation。示例如下：

def tools_condition(state: State):
    messages = state["messages"]
    last_message = messages[-1]
    # 仅当需要调用工具时返回"tools"，否则结束流程
    if isinstance(last_message, AIMessage) and hasattr(last_message, 'tool_calls') and last_message.tool_calls:
        return "tools"
    return END

2. 明确总结节点的触发时机
   已通过add_edge("tools", "summarize_conversation")设置工具调用完成后自动进入总结节点，无需让Chatbot节点的条件边触发总结流程，保持现有固定边逻辑即可。

内容的提问来源于stack exchange，提问作者web profiler