command_agent.py

import random
from typing import Literal

from langchain_core.messages import AIMessage
from langgraph.graph import START, MessagesState, StateGraph
from langgraph.types import Command


class AgentState(MessagesState, total=False):
    """
    `total=False` is PEP589 specs.

    documentation: https://typing.readthedocs.io/en/latest/spec/typeddict.html#totality
    """


# Define the nodes


def node_a(state: AgentState) -> Command[Literal["node_b", "node_c"]]:
    print("Called A")
    value = random.choice(["a", "b"])
    goto: Literal["node_b", "node_c"]
    # this is a replacement for a conditional edge function
    if value == "a":
        goto = "node_b"
    else:
        goto = "node_c"

    # note how Command allows you to BOTH update the graph state AND route to the next node
    return Command(
        # this is the state update
        update={"messages": [AIMessage(content=f"Hello {value}")]},
        # this is a replacement for an edge
        goto=goto,
    )


def node_b(state: AgentState):
    print("Called B")
    return {"messages": [AIMessage(content="Hello B")]}


def node_c(state: AgentState):
    print("Called C")
    return {"messages": [AIMessage(content="Hello C")]}


builder = StateGraph(AgentState)
builder.add_edge(START, "node_a")
builder.add_node(node_a)
builder.add_node(node_b)
builder.add_node(node_c)
# NOTE: there are no edges between nodes A, B and C!

command_agent = builder.compile()