How to Stream AI Responses with SSE in Python

from fastapi import FastAPI
from fastapi.responses import StreamingResponse
from openai import OpenAI
import json

app = FastAPI()

client = OpenAI(
    api_key="izzi-YOUR_KEY_HERE",
    base_url="https://api.izziapi.com/v1"
)

@app.post("/chat/stream")
async def stream_chat(request: dict):
    message = request.get("message", "")
    model = request.get("model", "claude-sonnet-4-20250514")
    
    async def generate():
        stream = client.chat.completions.create(
            model=model,
            messages=[{"role": "user", "content": message}],
            stream=True
        )
        
        for chunk in stream:
            content = chunk.choices[0].delta.content or ""
            if content:
                yield f"data: {json.dumps({'content': content})}\n\n"
        
        yield "data: [DONE]\n\n"
    
    return StreamingResponse(
        generate(),
        media_type="text/event-stream",
        headers={
            "Cache-Control": "no-cache",
            "Connection": "keep-alive",
        }
    )

async function streamChat(message: string) {
  const response = await fetch("/chat/stream", {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify({ message }),
  });

  const reader = response.body!.getReader();
  const decoder = new TextDecoder();
  let fullResponse = "";

  while (true) {
    const { done, value } = await reader.read();
    if (done) break;

    const text = decoder.decode(value);
    const lines = text.split("\n\n").filter(Boolean);

    for (const line of lines) {
      if (line === "data: [DONE]") return fullResponse;
      if (line.startsWith("data: ")) {
        const { content } = JSON.parse(line.slice(6));
        fullResponse += content;
        updateUI(fullResponse); // Update your UI here
      }
    }
  }
  return fullResponse;
}

async def generate_with_error_handling():
    try:
        stream = client.chat.completions.create(
            model="claude-sonnet-4-20250514",
            messages=messages,
            stream=True,
            timeout=30
        )
        for chunk in stream:
            content = chunk.choices[0].delta.content or ""
            if content:
                yield f"data: {json.dumps({'content': content})}\n\n"
    except Exception as e:
        yield f"data: {json.dumps({'error': str(e)})}\n\n"
    finally:
        yield "data: [DONE]\n\n"