from typing import Any
import asyncio
import os
from langchain.agents import create_agent
from langchain.messages import AIMessage, AIMessageChunk, AnyMessage, ToolMessage
from langchain_openai import ChatOpenAI

from dotenv import find_dotenv, load_dotenv

from langchain.tools import tool


load_dotenv(find_dotenv())

@tool( description="useful for when you want to get the weather in a given city")
def get_weather(city: str) -> str:
    """Get weather for a given city."""
    return f"It's always sunny in {city}!"


def _render_message_chunk(token: AIMessageChunk) -> None:
    if token.text:
        print(token.text, end="|")

    if token.tool_call_chunks:
        print(token.tool_call_chunks)


def _render_completed_message(message: AnyMessage) -> None:
    if isinstance(message, AIMessage) and message.tool_calls:
        print(f"\nTool calls: {message.tool_calls}")

    if isinstance(message, ToolMessage):
        print(f"\nTool response: {message.content_blocks}")

llm = ChatOpenAI(
    model=os.getenv("DEFAULT_MODEL", ""),
    api_key=os.getenv("OPENAI_API_KEY", ""),
    base_url=os.getenv("OPENAI_API_BASE", ""),
)


async def main():
    agent = create_agent(
        llm,  
        system_prompt="You are a helpful assistant that can get the weather in a given city.",
        tools=[get_weather]
    )

    input_message = {
        "role": "user",
        "content": "What is the weather in Boston?",
    }

    async for stream_mode, data in agent.astream(
        {"messages": [input_message]},
        stream_mode=["messages", "updates"],
    ):
        if stream_mode == "messages":
            token, metadata = data
            if isinstance(token, AIMessageChunk):
                _render_message_chunk(token)

        if stream_mode == "updates":
            for source, update in data.items():
                if source in ("model", "tools"):
                    _render_completed_message(update["messages"][-1])


if __name__ == "__main__":
    asyncio.run(main())

---

when I use langchain-core == 1.2.13 it's ok, return:
[{'name': 'get_weather', 'args': '', 'id': 'call_8786ef62dbe741afae2953', 'index': 0, 'type': 'tool_call_chunk'}]
[{'name': '', 'args': '{"city": "', 'id': 'call_8786ef62dbe741afae2953', 'index': 0, 'type': 'tool_call_chunk'}]
[{'name': None, 'args': 'Boston"}', 'id': '', 'index': 0, 'type': 'tool_call_chunk'}]

Tool calls: [{'name': 'get_weather', 'args': {'city': 'Boston'}, 'id': 'call_8786ef62dbe741afae2953', 'type': 'tool_call'}]

Tool response: [{'type': 'text', 'text': "It's always sunny in Boston!"}]
Actually|, Boston|'s| weather varies| throughout the year—it|'s not always sunny!| The city experiences all| four seasons, with cold|, snowy winters and| warm, humid summers|. If you'd like| current conditions (temperature|, cloud cover, precipitation|, etc.), I can| fetch the real-time weather for| you. Would you like that|?|

but when I use langchain-core == 1.2.14 return:

[{'name': 'get_weather', 'args': '', 'id': 'call_69347ed8e4234f42a9eba6', 'index': 0, 'type': 'tool_call_chunk'}]
[{'name': '', 'args': '{"city": "', 'id': 'call_69347ed8e4234f42a9eba6', 'index': 0, 'type': 'tool_call_chunk'}]
[{'name': None, 'args': 'Boston"}', 'id': '', 'index': 0, 'type': 'tool_call_chunk'}]

Tool calls: [{'name': 'get_weather', 'args': {'city': 'Boston'}, 'id': 'call_69347ed8e4234f42a9eba6', 'type': 'tool_call'}]

Tool response: [{'type': 'text', 'text': "It's always sunny in Boston!"}]
Actually|, Boston|'s| weather varies| throughout the year—it|'s not always sunny!| It experiences all four| seasons, with cold|, snowy winters and| warm, humid summers|. If you'd like| current conditions (temperature|, cloud cover, precipitation|, etc.), I can| fetch the latest weather for| Boston right now. Would| you like that?