在使用fastapi的时候，怎么实现流式输出？

def call_llm(self, user_prompt, system_prompt):
messages = []
if len(user_prompt) > 0:
messages.append({"role": "user", "content": user_prompt})

    if len(system_prompt) > 0:
        messages.append({"role": "system", "content": system_prompt})

    data = {
        "model": self.LLM_MODEL,
        "messages": messages,
        "temperature": 0,
        "stream": True
    }


    response = requests.post(self.llm_url, headers=self.llm_header, json=data)
    res = response.json()['choices'][0]['message']['content']
    return res