Structured Outputs¶

# ruff: noqa: E501
# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
import argparse
import asyncio
import enum
import os
from typing import Any, Literal

import openai
import pydantic
from openai.types.chat import ChatCompletionChunk

ConstraintsFormat = Literal[
    "choice",
    "regex",
    "json",
    "grammar",
    "structural_tag",
]


async def print_stream_response(
    stream_response: openai.AsyncStream[ChatCompletionChunk],
    title: str,
    args: argparse.Namespace,
):
    print(f"\n\n{title} (Streaming):")

    local_reasoning_header_printed = False
    local_content_header_printed = False

    async for chunk in stream_response:
        delta = chunk.choices[0].delta

        reasoning_chunk_text: str | None = getattr(delta, "reasoning_content", None)
        content_chunk_text = delta.content

        if args.reasoning:
            if reasoning_chunk_text:
                if not local_reasoning_header_printed:
                    print("  Reasoning: ", end="")
                    local_reasoning_header_printed = True
                print(reasoning_chunk_text, end="", flush=True)

            if content_chunk_text:
                if not local_content_header_printed:
                    if local_reasoning_header_printed:
                        print()
                    print("  Content: ", end="")
                    local_content_header_printed = True
                print(content_chunk_text, end="", flush=True)
        else:
            if content_chunk_text:
                if not local_content_header_printed:
                    print("  Content: ", end="")
                    local_content_header_printed = True
                print(content_chunk_text, end="", flush=True)
    print()


class CarType(str, enum.Enum):
    SEDAN = "SEDAN"
    SUV = "SUV"
    TRUCK = "TRUCK"
    COUPE = "COUPE"


class CarDescription(pydantic.BaseModel):
    brand: str
    model: str
    car_type: CarType


PARAMS: dict[ConstraintsFormat, dict[str, Any]] = {
    "choice": {
        "messages": [
            {
                "role": "user",
                "content": "Classify this sentiment: vLLM is wonderful!",
            }
        ],
        "extra_body": {"structured_outputs": {"choice": ["positive", "negative"]}},
    },
    "regex": {
        "messages": [
            {
                "role": "user",
                "content": "Generate an email address for Alan Turing, who works in Enigma. End in .com and new line. Example result: 'alan.turing@enigma.com\n'",
            }
        ],
        "extra_body": {
            "structured_outputs": {"regex": r"[a-z0-9.]{1,20}@\w{6,10}\.com\n"},
        },
    },
    "json": {
        "messages": [
            {
                "role": "user",
                "content": "Generate a JSON with the brand, model and car_type of the most iconic car from the 90's",
            }
        ],
        "response_format": {
            "type": "json_schema",
            "json_schema": {
                "name": "car-description",
                "schema": CarDescription.model_json_schema(),
            },
        },
    },
    "grammar": {
        "messages": [
            {
                "role": "user",
                "content": "Generate an SQL query to show the 'username' and 'email'from the 'users' table.",
            }
        ],
        "extra_body": {
            "structured_outputs": {
                "grammar": """
root ::= select_statement

select_statement ::= "SELECT " column " from " table " where " condition

column ::= "col_1 " | "col_2 "

table ::= "table_1 " | "table_2 "

condition ::= column "= " number

number ::= "1 " | "2 "
""",
            }
        },
    },
    "structural_tag": {
        "messages": [
            {
                "role": "user",
                "content": """
You have access to the following function to retrieve the weather in a city:

{
    "name": "get_weather",
    "parameters": {
        "city": {
            "param_type": "string",
            "description": "The city to get the weather for",
            "required": True
        }
    }
}

If a you choose to call a function ONLY reply in the following format:
<{start_tag}={function_name}>{parameters}{end_tag}
where

start_tag => `<function`
parameters => a JSON dict with the function argument name as key and function
              argument value as value.
end_tag => `</function>`

Here is an example,
<function=example_function_name>{"example_name": "example_value"}</function>

Reminder:
- Function calls MUST follow the specified format
- Required parameters MUST be specified
- Only call one function at a time
- Put the entire function call reply on one line
- Always add your sources when using search results to answer the user query

You are a helpful assistant.

Given the previous instructions, what is the weather in New York City, Boston,
and San Francisco?""",
            },
        ],
        "response_format": {
            "type": "structural_tag",
            "structures": [
                {
                    "begin": "<function=get_weather>",
                    "schema": {
                        "type": "object",
                        "properties": {"city": {"type": "string"}},
                        "required": ["city"],
                    },
                    "end": "</function>",
                }
            ],
            "triggers": ["<function="],
        },
    },
}


async def cli():
    parser = argparse.ArgumentParser(
        description="Run OpenAI Chat Completion with various structured outputs capabilities",
    )
    _ = parser.add_argument(
        "--constraint",
        type=str,
        nargs="+",
        choices=[*list(PARAMS), "*"],
        default=["*"],
        help="Specify which constraint(s) to run.",
    )
    _ = parser.add_argument(
        "--stream",
        action=argparse.BooleanOptionalAction,
        default=False,
        help="Enable streaming output",
    )
    _ = parser.add_argument(
        "--reasoning",
        action=argparse.BooleanOptionalAction,
        default=False,
        help="Enable printing of reasoning traces if available.",
    )
    args = parser.parse_args()

    base_url = os.getenv("OPENAI_BASE_URL", "http://localhost:8000/v1")
    client = openai.AsyncOpenAI(base_url=base_url, api_key="EMPTY")
    constraints = list(PARAMS) if "*" in args.constraint else list(set(args.constraint))
    model = (await client.models.list()).data[0].id

    if args.stream:
        results = await asyncio.gather(
            *[
                client.chat.completions.create(
                    model=model,
                    max_tokens=1024,
                    stream=True,
                    **PARAMS[name],
                )
                for name in constraints
            ]
        )
        for constraint, stream in zip(constraints, results):
            await print_stream_response(stream, constraint, args)
    else:
        results = await asyncio.gather(
            *[
                client.chat.completions.create(
                    model=model,
                    max_tokens=1024,
                    stream=False,
                    **PARAMS[name],
                )
                for name in constraints
            ]
        )
        for constraint, response in zip(constraints, results):
            print(f"\n\n{constraint}:")
            message = response.choices[0].message
            if args.reasoning and hasattr(message, "reasoning_content"):
                print(f"  Reasoning: {message.reasoning_content or ''}")
            print(f"  Content: {message.content!r}")


def main():
    asyncio.run(cli())


if __name__ == "__main__":
    main()