langgraph-stream-parser 0.1.2

Universal parser for LangGraph streaming outputs

langgraph-stream-parser

Universal parser for LangGraph streaming outputs. Normalizes complex, variable output shapes from graph.stream() and graph.astream() into consistent, typed event objects.

Installation

pip install langgraph-stream-parser

Quick Start

from langgraph_stream_parser import StreamParser
from langgraph_stream_parser.events import ContentEvent, ToolCallStartEvent, InterruptEvent

parser = StreamParser()

for event in parser.parse(graph.stream(input_data, stream_mode="updates")):
    match event:
        case ContentEvent(content=text):
            print(text, end="")
        case ToolCallStartEvent(name=name):
            print(f"\nCalling {name}...")
        case InterruptEvent(action_requests=actions):
            # Handle human-in-the-loop
            decision = get_user_decision(actions)
            # Resume with create_resume_input()

Features

• Typed Events: All stream outputs normalized to dataclass events with full type hints
• Tool Lifecycle Tracking: Automatic tracking of tool calls from start to completion
• Interrupt Handling: Parse and resume from human-in-the-loop interrupts
• Extensible Extractors: Register custom extractors for domain-specific tools
• Async Support: Both sync and async parsing via parse() and aparse()
• Zero Dependencies: LangGraph/LangChain imported dynamically only when needed
• Backward Compatible: Legacy dict-based API available for gradual migration

Event Types

Event	Description
ContentEvent	Text content from AI messages
ToolCallStartEvent	Tool call initiated by AI
ToolCallEndEvent	Tool call completed with result
ToolExtractedEvent	Special content extracted from tool (e.g., reflections, todos)
InterruptEvent	Human-in-the-loop interrupt requiring decision
StateUpdateEvent	Non-message state updates (opt-in)
CompleteEvent	Stream finished successfully
ErrorEvent	Error during streaming

All events have a to_dict() method for JSON serialization. Use event_to_dict(event) for a convenient conversion function.

Usage Examples

Basic Parsing

from langgraph_stream_parser import StreamParser

parser = StreamParser()

for event in parser.parse(graph.stream({"messages": [...]}, stream_mode="updates")):
    print(event)

Pattern Matching (Python 3.10+)

from langgraph_stream_parser import StreamParser
from langgraph_stream_parser.events import *

parser = StreamParser()

for event in parser.parse(stream):
    match event:
        case ContentEvent(content=text, node=node):
            print(f"[{node}] {text}", end="")

        case ToolCallStartEvent(name=name, args=args):
            print(f"\n⏳ Calling {name}...")

        case ToolCallEndEvent(name=name, status="success"):
            print(f"✅ {name} completed")

        case ToolCallEndEvent(name=name, status="error", error_message=err):
            print(f"❌ {name} failed: {err}")

        case InterruptEvent() as interrupt:
            if interrupt.needs_approval:
                handle_approval(interrupt.action_requests)

        case CompleteEvent():
            print("\n✓ Done")

        case ErrorEvent(error=err):
            print(f"⚠️ Error: {err}")

Handling Interrupts

from langgraph_stream_parser import StreamParser
from langgraph_stream_parser.events import InterruptEvent

parser = StreamParser()
config = {"configurable": {"thread_id": "my-thread"}}

for event in parser.parse(graph.stream(input_data, config=config)):
    if isinstance(event, InterruptEvent):
        # Show user the pending actions
        for action in event.action_requests:
            print(f"Tool: {action['tool']}")
            print(f"Args: {action['args']}")

        # Check allowed decisions
        print(f"Allowed: {event.allowed_decisions}")

        # Get user decision and resume
        decision = "approve" if input("Approve? (y/n): ") == "y" else "reject"
        resume_input = event.create_resume(decision)

        for resume_event in parser.parse(graph.stream(resume_input, config=config)):
            handle_event(resume_event)
        break

Custom Tool Extractors

from langgraph_stream_parser import StreamParser, ToolExtractor
from langgraph_stream_parser.events import ToolExtractedEvent

class CanvasExtractor:
    tool_name = "add_to_canvas"
    extracted_type = "canvas_item"

    def extract(self, content):
        if isinstance(content, dict):
            return content
        return {"type": "text", "data": str(content)}

parser = StreamParser()
parser.register_extractor(CanvasExtractor())

for event in parser.parse(stream):
    if isinstance(event, ToolExtractedEvent) and event.extracted_type == "canvas_item":
        add_to_canvas_ui(event.data)

Async Support

from langgraph_stream_parser import StreamParser

parser = StreamParser()

async def stream_agent():
    async for event in parser.aparse(graph.astream(input_data)):
        handle_event(event)

Configuration Options

parser = StreamParser(
    # Track tool call lifecycle (start -> end)
    track_tool_lifecycle=True,

    # Skip these tools entirely (no events emitted)
    skip_tools=["internal_tool"],

    # Include StateUpdateEvent for non-message state keys
    include_state_updates=False,
)

Legacy Dict-Based API

For backward compatibility or simpler use cases:

from langgraph_stream_parser import stream_graph_updates, resume_graph_from_interrupt

for update in stream_graph_updates(agent, input_data, config=config):
    if update.get("status") == "interrupt":
        interrupt = update["interrupt"]
        # Handle interrupt...
    elif "chunk" in update:
        print(update["chunk"], end="")
    elif "tool_calls" in update:
        print(f"Calling tools: {update['tool_calls']}")
    elif update.get("status") == "complete":
        break

# Resume from interrupt
for update in resume_graph_from_interrupt(agent, decisions=[{"type": "approve"}], config=config):
    handle_update(update)

Display Adapters

Pre-built adapters for rendering stream events in different environments:

CLIAdapter - Styled Terminal Output

from langgraph_stream_parser.adapters import CLIAdapter

adapter = CLIAdapter()
adapter.run(
    graph=agent,
    input_data={"messages": [("user", "Hello")]},
    config={"configurable": {"thread_id": "my-thread"}}
)

Features:

• ANSI color formatting
• Spinner animation during tool execution
• Interactive arrow-key interrupt handling

PrintAdapter - Plain Text Output

from langgraph_stream_parser.adapters import PrintAdapter

adapter = PrintAdapter()
adapter.run(graph=agent, input_data=input_data, config=config)

Universal output that works in any Python environment without dependencies.

JupyterDisplay - Rich Notebook Display

from langgraph_stream_parser.adapters.jupyter import JupyterDisplay

display = JupyterDisplay()
display.run(graph=agent, input_data=input_data, config=config)

Requires: pip install langgraph-stream-parser[jupyter]

Adapter Options

All adapters support:

adapter = CLIAdapter(
    show_tool_args=True,           # Show tool arguments
    max_content_preview=200,       # Max chars for extracted content
    reflection_types={"thinking"}, # Custom reflection type names
    todo_types={"tasks"},          # Custom todo type names
)

Custom Adapters

Extend BaseAdapter for custom rendering:

from langgraph_stream_parser.adapters import BaseAdapter

class MyAdapter(BaseAdapter):
    def render(self):
        # Implement your rendering logic
        pass

    def prompt_interrupt(self, event):
        # Handle interrupt prompts
        return [{"type": "approve"}]

Built-in Extractors

The package includes extractors for common LangGraph tools:

• ThinkToolExtractor: Extracts reflections from think_tool
• TodoExtractor: Extracts todo lists from write_todos

Examples

FastAPI WebSocket Streaming

See examples/fastapi_websocket.py for a complete example of streaming LangGraph events to a web client via WebSockets.

# Install dependencies
pip install fastapi uvicorn websockets

# Run the example
uvicorn examples.fastapi_websocket:app --reload

# Open http://localhost:8000 in your browser

Development

# Install with dev dependencies
pip install -e ".[dev]"

# Run tests
pytest

# Run tests with coverage
pytest --cov=langgraph_stream_parser

License

MIT