使用时间旅行¶
在 LangGraph 中使用时间旅行
- 运行图：使用
invoke或stream方法，并提供初始输入来运行图。 - 在现有线程中识别检查点：使用
get_state_history()方法检索特定thread_id的执行历史，并找到所需的checkpoint_id。
或者，在你希望执行暂停的节点之前设置一个中断。然后，你可以找到在该中断之前记录的最新检查点。 - 更新图状态（可选）：使用
update_state方法修改检查点处的图状态，并从不同的状态恢复执行。 - 从检查点恢复执行：使用
invoke或stream方法，输入为None，并提供包含相应thread_id和checkpoint_id的配置。
提示
关于时间旅行的概念性概述，请参见时间旅行。
在工作流中¶
本示例构建了一个简单的 LangGraph 工作流，它会生成一个笑话主题，并使用 LLM 创作一个笑话。它演示了如何运行图、检索过去的执行检查点、可选地修改状态，并从选定的检查点恢复执行以探索不同的结果。
设置¶
首先我们需要安装所需的包
接下来，我们需要设置 Anthropic（我们将使用的 LLM）的 API 密钥
import getpass
import os
def _set_env(var: str):
if not os.environ.get(var):
os.environ[var] = getpass.getpass(f"{var}: ")
_set_env("ANTHROPIC_API_KEY")
为 LangGraph 开发设置 LangSmith
注册 LangSmith，以便快速发现问题并提高 LangGraph 项目的性能。LangSmith 允许您使用跟踪数据来调试、测试和监控用 LangGraph 构建的 LLM 应用 — 在此处阅读更多关于如何入门的信息。
API 参考：StateGraph | START | END | init_chat_model | InMemorySaver
import uuid
from typing_extensions import TypedDict, NotRequired
from langgraph.graph import StateGraph, START, END
from langchain.chat_models import init_chat_model
from langgraph.checkpoint.memory import InMemorySaver
class State(TypedDict):
topic: NotRequired[str]
joke: NotRequired[str]
llm = init_chat_model(
"anthropic:claude-3-7-sonnet-latest",
temperature=0,
)
def generate_topic(state: State):
"""LLM call to generate a topic for the joke"""
msg = llm.invoke("Give me a funny topic for a joke")
return {"topic": msg.content}
def write_joke(state: State):
"""LLM call to write a joke based on the topic"""
msg = llm.invoke(f"Write a short joke about {state['topic']}")
return {"joke": msg.content}
# Build workflow
workflow = StateGraph(State)
# Add nodes
workflow.add_node("generate_topic", generate_topic)
workflow.add_node("write_joke", write_joke)
# Add edges to connect nodes
workflow.add_edge(START, "generate_topic")
workflow.add_edge("generate_topic", "write_joke")
workflow.add_edge("write_joke", END)
# Compile
checkpointer = InMemorySaver()
graph = workflow.compile(checkpointer=checkpointer)
graph
1. 运行图¶
config = {
"configurable": {
"thread_id": uuid.uuid4(),
}
}
state = graph.invoke({}, config)
print(state["topic"])
print()
print(state["joke"])
输出
How about "The Secret Life of Socks in the Dryer"? You know, exploring the mysterious phenomenon of how socks go into the laundry as pairs but come out as singles. Where do they go? Are they starting new lives elsewhere? Is there a sock paradise we don't know about? There's a lot of comedic potential in the everyday mystery that unites us all!
# The Secret Life of Socks in the Dryer
I finally discovered where all my missing socks go after the dryer. Turns out they're not missing at all—they've just eloped with someone else's socks from the laundromat to start new lives together.
My blue argyle is now living in Bermuda with a red polka dot, posting vacation photos on Sockstagram and sending me lint as alimony.
2. 确定检查点¶
# The states are returned in reverse chronological order.
states = list(graph.get_state_history(config))
for state in states:
print(state.next)
print(state.config["configurable"]["checkpoint_id"])
print()
输出
()
1f02ac4a-ec9f-6524-8002-8f7b0bbeed0e
('write_joke',)
1f02ac4a-ce2a-6494-8001-cb2e2d651227
('generate_topic',)
1f02ac4a-a4e0-630d-8000-b73c254ba748
('__start__',)
1f02ac4a-a4dd-665e-bfff-e6c8c44315d9
# This is the state before last (states are listed in chronological order)
selected_state = states[1]
print(selected_state.next)
print(selected_state.values)
输出
('write_joke',)
{'topic': 'How about "The Secret Life of Socks in the Dryer"? You know, exploring the mysterious phenomenon of how socks go into the laundry as pairs but come out as singles. Where do they go? Are they starting new lives elsewhere? Is there a sock paradise we don\\'t know about? There\\'s a lot of comedic potential in the everyday mystery that unites us all!'}
3. 更新状态（可选）¶
update_state 将创建一个新的检查点。新检查点将与同一线程关联，但具有新的检查点 ID。
new_config = graph.update_state(selected_state.config, values={"topic": "chickens"})
print(new_config)
输出
{'configurable': {'thread_id': 'c62e2e03-c27b-4cb6-8cea-ea9bfedae006', 'checkpoint_ns': '', 'checkpoint_id': '1f02ac4a-ecee-600b-8002-a1d21df32e4c'}}
4. 从检查点恢复执行¶
输出