httpx Streaming — async iter_lines + SSE parse

import os, json, httpx, asyncio
from typing import AsyncIterator

async def stream_chat_async(
    messages: list[dict], model: str = "gpt-4o-mini",
) -> AsyncIterator[str]:
    """Yield text delta strings from a streaming response."""
    url = "https://api.openai.com/v1/chat/completions"
    headers = {
        "Authorization": f"Bearer {os.environ['OPENAI_API_KEY']}",
        "Content-Type": "application/json",
    }
    body = {"model": model, "messages": messages, "stream": True}
    async with httpx.AsyncClient(timeout=None) as client:
        async with client.stream("POST", url, headers=headers, json=body) as resp:
            resp.raise_for_status()
            async for line in resp.aiter_lines():
                if not line or line == "data: [DONE]":
                    continue
                if line.startswith("data: "):
                    try:
                        chunk = json.loads(line[len("data: "):])
                        content = chunk["choices"][0]["delta"].get("content", "")
                        if content:
                            yield content
                    except (json.JSONDecodeError, KeyError, IndexError):
                        pass

async def main():
    async for token in stream_chat_async([{"role": "user", "content": "Count to 5."}]):
        print(token, end="", flush=True)
    print()

asyncio.run(main())