构建多代理系统¶

from typing import Annotated
from langchain_core.messages import convert_to_messages
from langchain_core.tools import tool, InjectedToolCallId
from langgraph.prebuilt import create_react_agent, InjectedState
from langgraph.graph import StateGraph, START, MessagesState
from langgraph.types import Command

# We'll use `pretty_print_messages` helper to render the streamed agent outputs nicely

def pretty_print_message(message, indent=False):
    pretty_message = message.pretty_repr(html=True)
    if not indent:
        print(pretty_message)
        return

    indented = "\n".join("\t" + c for c in pretty_message.split("\n"))
    print(indented)


def pretty_print_messages(update, last_message=False):
    is_subgraph = False
    if isinstance(update, tuple):
        ns, update = update
        # skip parent graph updates in the printouts
        if len(ns) == 0:
            return

        graph_id = ns[-1].split(":")[0]
        print(f"Update from subgraph {graph_id}:")
        print("\n")
        is_subgraph = True

    for node_name, node_update in update.items():
        update_label = f"Update from node {node_name}:"
        if is_subgraph:
            update_label = "\t" + update_label

        print(update_label)
        print("\n")

        messages = convert_to_messages(node_update["messages"])
        if last_message:
            messages = messages[-1:]

        for m in messages:
            pretty_print_message(m, indent=is_subgraph)
        print("\n")


def create_handoff_tool(*, agent_name: str, description: str | None = None):
    name = f"transfer_to_{agent_name}"
    description = description or f"Transfer to {agent_name}"

    @tool(name, description=description)
    def handoff_tool(
        state: Annotated[MessagesState, InjectedState], # (1)!
        tool_call_id: Annotated[str, InjectedToolCallId],
    ) -> Command:
        tool_message = {
            "role": "tool",
            "content": f"Successfully transferred to {agent_name}",
            "name": name,
            "tool_call_id": tool_call_id,
        }
        return Command( # (2)!
            goto=agent_name, # (3)!
            update={"messages": state["messages"] + [tool_message]}, # (4)!
            graph=Command.PARENT, # (5)!
        )
    return handoff_tool

# Handoffs
transfer_to_hotel_assistant = create_handoff_tool(
    agent_name="hotel_assistant",
    description="Transfer user to the hotel-booking assistant.",
)
transfer_to_flight_assistant = create_handoff_tool(
    agent_name="flight_assistant",
    description="Transfer user to the flight-booking assistant.",
)

# Simple agent tools
def book_hotel(hotel_name: str):
    """Book a hotel"""
    return f"Successfully booked a stay at {hotel_name}."

def book_flight(from_airport: str, to_airport: str):
    """Book a flight"""
    return f"Successfully booked a flight from {from_airport} to {to_airport}."

# Define agents
flight_assistant = create_react_agent(
    model="anthropic:claude-3-5-sonnet-latest",
    tools=[book_flight, transfer_to_hotel_assistant],
    prompt="You are a flight booking assistant",
    name="flight_assistant"
)
hotel_assistant = create_react_agent(
    model="anthropic:claude-3-5-sonnet-latest",
    tools=[book_hotel, transfer_to_flight_assistant],
    prompt="You are a hotel booking assistant",
    name="hotel_assistant"
)

# Define multi-agent graph
multi_agent_graph = (
    StateGraph(MessagesState)
    .add_node(flight_assistant)
    .add_node(hotel_assistant)
    .add_edge(START, "flight_assistant")
    .compile()
)

# Run the multi-agent graph
for chunk in multi_agent_graph.stream(
    {
        "messages": [
            {
                "role": "user",
                "content": "book a flight from BOS to JFK and a stay at McKittrick Hotel"
            }
        ]
    },
    subgraphs=True
):
    pretty_print_messages(chunk)

from langchain_anthropic import ChatAnthropic
from langgraph.graph import MessagesState, StateGraph, START
from langgraph.prebuilt import create_react_agent, InjectedState
from langgraph.types import Command, interrupt
from langgraph.checkpoint.memory import MemorySaver


model = ChatAnthropic(model="claude-3-5-sonnet-latest")

class MultiAgentState(MessagesState):
    last_active_agent: str


# Define travel advisor tools and ReAct agent
travel_advisor_tools = [
    get_travel_recommendations,
    make_handoff_tool(agent_name="hotel_advisor"),
]
travel_advisor = create_react_agent(
    model,
    travel_advisor_tools,
    prompt=(
        "You are a general travel expert that can recommend travel destinations (e.g. countries, cities, etc). "
        "If you need hotel recommendations, ask 'hotel_advisor' for help. "
        "You MUST include human-readable response before transferring to another agent."
    ),
)


def call_travel_advisor(
    state: MultiAgentState,
) -> Command[Literal["hotel_advisor", "human"]]:
    # You can also add additional logic like changing the input to the agent / output from the agent, etc.
    # NOTE: we're invoking the ReAct agent with the full history of messages in the state
    response = travel_advisor.invoke(state)
    update = {**response, "last_active_agent": "travel_advisor"}
    return Command(update=update, goto="human")


# Define hotel advisor tools and ReAct agent
hotel_advisor_tools = [
    get_hotel_recommendations,
    make_handoff_tool(agent_name="travel_advisor"),
]
hotel_advisor = create_react_agent(
    model,
    hotel_advisor_tools,
    prompt=(
        "You are a hotel expert that can provide hotel recommendations for a given destination. "
        "If you need help picking travel destinations, ask 'travel_advisor' for help."
        "You MUST include human-readable response before transferring to another agent."
    ),
)


def call_hotel_advisor(
    state: MultiAgentState,
) -> Command[Literal["travel_advisor", "human"]]:
    response = hotel_advisor.invoke(state)
    update = {**response, "last_active_agent": "hotel_advisor"}
    return Command(update=update, goto="human")


def human_node(
    state: MultiAgentState, config
) -> Command[Literal["hotel_advisor", "travel_advisor", "human"]]:
    """A node for collecting user input."""

    user_input = interrupt(value="Ready for user input.")
    active_agent = state["last_active_agent"]

    return Command(
        update={
            "messages": [
                {
                    "role": "human",
                    "content": user_input,
                }
            ]
        },
        goto=active_agent,
    )


builder = StateGraph(MultiAgentState)
builder.add_node("travel_advisor", call_travel_advisor)
builder.add_node("hotel_advisor", call_hotel_advisor)

# This adds a node to collect human input, which will route
# back to the active agent.
builder.add_node("human", human_node)

# We'll always start with a general travel advisor.
builder.add_edge(START, "travel_advisor")


checkpointer = MemorySaver()
graph = builder.compile(checkpointer=checkpointer)

import uuid

thread_config = {"configurable": {"thread_id": str(uuid.uuid4())}}

inputs = [
    # 1st round of conversation,
    {
        "messages": [
            {"role": "user", "content": "i wanna go somewhere warm in the caribbean"}
        ]
    },
    # Since we're using `interrupt`, we'll need to resume using the Command primitive.
    # 2nd round of conversation,
    Command(
        resume="could you recommend a nice hotel in one of the areas and tell me which area it is."
    ),
    # 3rd round of conversation,
    Command(
        resume="i like the first one. could you recommend something to do near the hotel?"
    ),
]

for idx, user_input in enumerate(inputs):
    print()
    print(f"--- Conversation Turn {idx + 1} ---")
    print()
    print(f"User: {user_input}")
    print()
    for update in graph.stream(
        user_input,
        config=thread_config,
        stream_mode="updates",
    ):
        for node_id, value in update.items():
            if isinstance(value, dict) and value.get("messages", []):
                last_message = value["messages"][-1]
                if isinstance(last_message, dict) or last_message.type != "ai":
                    continue
                print(f"{node_id}: {last_message.content}")