How to add dynamic breakpoints¶
Human-in-the-loop (HIL) interactions are crucial for agentic systems. Breakpoints are a common HIL interaction pattern, allowing the graph to stop at specific steps and seek human approval before proceeding (e.g., for sensitive actions).
In LangGraph you can add breakpoints before / after a node is executed. But oftentimes it may be helpful to dynamically interrupt the graph from inside a given node based on some condition. When doing so, it may also be helpful to include information about why that interrupt was raised.
This guide shows how you can dynamically interrupt the graph using NodeInterrupt -- a special exception that can be raised from inside a node. Let's see it in action!
Setup¶
First, let's install the required packages
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Define the graph¶
from typing_extensions import TypedDict
from IPython.display import Image, display
from langgraph.graph import StateGraph, START, END
from langgraph.checkpoint.memory import MemorySaver
from langgraph.errors import NodeInterrupt
class State(TypedDict):
input: str
def step_1(state: State) -> State:
print("---Step 1---")
return state
def step_2(state: State) -> State:
# Let's optionally raise a NodeInterrupt
# if the length of the input is longer than 5 characters
if len(state["input"]) > 5:
raise NodeInterrupt(
f"Received input that is longer than 5 characters: {state['input']}"
)
print("---Step 2---")
return state
def step_3(state: State) -> State:
print("---Step 3---")
return state
builder = StateGraph(State)
builder.add_node("step_1", step_1)
builder.add_node("step_2", step_2)
builder.add_node("step_3", step_3)
builder.add_edge(START, "step_1")
builder.add_edge("step_1", "step_2")
builder.add_edge("step_2", "step_3")
builder.add_edge("step_3", END)
# Set up memory
memory = MemorySaver()
# Compile the graph with memory
graph = builder.compile(checkpointer=memory)
# View
display(Image(graph.get_graph().draw_mermaid_png()))
Run the graph with dynamic interrupt¶
First, let's run the graph with an input that <= 5 characters long. This should safely ignore the interrupt condition we defined and return the original input at the end of the graph execution.
initial_input = {"input": "hello"}
thread_config = {"configurable": {"thread_id": "1"}}
for event in graph.stream(initial_input, thread_config, stream_mode="values"):
print(event)
{'input': 'hello'}
---Step 1---
{'input': 'hello'}
---Step 2---
{'input': 'hello'}
---Step 3---
{'input': 'hello'}
NodeInterrupt error inside the step_2 node.
initial_input = {"input": "hello world"}
thread_config = {"configurable": {"thread_id": "2"}}
# Run the graph until the first interruption
for event in graph.stream(initial_input, thread_config, stream_mode="values"):
print(event)
step_2. If we inspect the graph state at this point, we can see the information on what node is set to execute next (step_2), as well as what node raised the interrupt (also step_2), and additional information about the interrupt.
('step_2',)
(PregelTask(id='365d4518-bcff-5abd-8ef5-8a0de7f510b0', name='step_2', error=None, interrupts=(Interrupt(value='Received input that is longer than 5 characters: hello world', when='during'),)),)
# NOTE: to resume the graph from a dynamic interrupt we use the same syntax as with regular interrupts -- we pass None as the input
for event in graph.stream(None, thread_config, stream_mode="values"):
print(event)
('step_2',)
(PregelTask(id='365d4518-bcff-5abd-8ef5-8a0de7f510b0', name='step_2', error=None, interrupts=(Interrupt(value='Received input that is longer than 5 characters: hello world', when='during'),)),)
Update the graph state¶
To get around it, we can do several things.
First, we could simply run the graph on a different thread with a shorter input, like we did in the beginning. Alternatively, if we want to resume the graph execution from the breakpoint, we can update the state to have an input that's shorter than 5 characters (the condition for our interrupt).
# NOTE: this update will be applied as of the last successful node before the interrupt, i.e. `step_1`, right before the node with an interrupt
graph.update_state(config=thread_config, values={"input": "foo"})
for event in graph.stream(None, thread_config, stream_mode="values"):
print(event)
state = graph.get_state(thread_config)
print(state.next)
print(state.values)
step_2 (interrupted node) which would skip over that node altogether
initial_input = {"input": "hello world"}
thread_config = {"configurable": {"thread_id": "3"}}
# Run the graph until the first interruption
for event in graph.stream(initial_input, thread_config, stream_mode="values"):
print(event)
# NOTE: this update will skip the node `step_2` altogether
graph.update_state(config=thread_config, values=None, as_node="step_2")
for event in graph.stream(None, thread_config, stream_mode="values"):
print(event)
state = graph.get_state(thread_config)
print(state.next)
print(state.values)