How to get structured outputs

API
1

I’ve searched everywhere and asked chatgpt, and find that there are many different way to get structured outputs, which should I use on the earth?

from openai import OpenAI
from pydantic import BaseModel, Field


client = OpenAI(api_key=vllm_key, base_url=vllm_url)


class Car(BaseModel):
    brand: str = Field(description="Brand name, usually same as the company name")
    model: str = Field(description="Model Name")


class Cars(BaseModel):
    car_list: list[Car]


messages = [{"role": "user", "content": "list 10 kinds of famous cars"}]

model_and_messages = {"model": "qwen3-32b-bnb-4bit", "messages": messages}

# type 1
response1 = client.responses.parse(
    model="qwen3-32b-bnb-4bit",
    input=messages,
    text_format=Cars,
)

# type 2
response2 = client.chat.completions.parse(
    **model_and_messages,
    response_format=Cars,
)

# type 3
response3 = client.chat.completions.create(
    **model_and_messages,
    extra_body={"structured_outputs": {"json": Cars.model_json_schema()}},
)

# type 4
response4 = client.chat.completions.parse(
    **model_and_messages,
    response_format={
        "type": "json_schema",
        "json_schema": {
            "name": "prediction_response",
            "strict": True,
            "schema": Cars.model_json_schema()
        }
    },
)
print(response1.output_parsed)
print(response2.choices[0].message.content)
print(response3.choices[0].message.content)
print(response4.choices[0].message.content)

car_list=[Car(brand='Ford', model='Mustang'), Car(brand='Chevrolet', model='Corvette'), Car(brand='Porsche', model='911'), Car(brand='BMW', model='M3'), Car(brand='Mercedes-Benz', model='E-Class'), Car(brand='Toyota', model='Supra'), Car(brand='Lamborghini', model='Aventador'), Car(brand='Ferrari', model='488 GTB'), Car(brand='Audi', model='RS 6'), Car(brand='Mazda', model='Miata')]
{"car_list": [{"brand": "Ferrari", "model": "F40"}, {"brand": "Porsche", "model": "911"}, {"brand": "Ford", "model": "Mustang"}, {"brand": "Chevrolet", "model": "Corvette"}, {"brand": "Lamborghini", "model": "Diablo"}, {"brand": "Mercedes-Benz", "model": "S-Class"}, {"brand": "BMW", "model": "M3"}, {"brand": "Toyota", "model": "Supra"}, {"brand": "Dodge", "model": "Challenger"}, {"brand": "Aston Martin", "model": "DB"}] }
{"car_list": [{"brand": "Ferrari", "model": "F40"}, {"brand": "Porsche", "model": "911"}, {"brand": "Ford", "model": "Mustang"}, {"brand": "Chevrolet", "model": "Corvette"}, {"brand": "Lamborghini", "model": "Countach"}, {"brand": "Mercedes-Benz", "model": "300 SL"}, {"brand": "Aston Martin", "model": "DB5"}, {"brand": "Toyota", "model": "Supra"}, {"brand": "Nissan", "model": "Skyline GT-R"}, {"brand": "BMW", "model": "E30 M3"}]  }
{"car_list": [{"brand": "Ferrari", "model": "F40"}, {"brand": "Porsche", "model": "911"}, {"brand": "Ford", "model": "Mustang"}, {"brand": "Chevrolet", "model": "Corvette"}, {"brand": "Lamborghini", "model": "Countach"}, {"brand": "BMW", "model": "M3"}, {"brand": "Mercedes-Benz", "model": "S-Class"}, {"brand": "Toyota", "model": "Supra"}, {"brand": "Audi", "model": "R8"}, {"brand": "Mazda", "model": "Miata"}]  }