Structured outputs and function calling

import json

def call_model(prompt: str) -> str:
    # Placeholder. Plug in your provider here. For this demo we fake two replies:
    # the first is wrong, the second is right.
    call_model.n = getattr(call_model, "n", 0) + 1
    if call_model.n == 1:
        return '{"name": "Asha", "people": "four"}'
    return '{"name": "Asha", "people": 4, "date": "2026-10-02"}'

FIELDS = {"name": str, "people": int, "date": str}

def check(raw: str):
    try:
        data = json.loads(raw)
    except json.JSONDecodeError as err:
        return None, "Not valid JSON: " + str(err)
    if not isinstance(data, dict):
        return None, "Expected one JSON object."
    for key, kind in FIELDS.items():
        value = data.get(key)
        if value is None:
            return None, "Missing field: " + key
        if not isinstance(value, kind) or isinstance(value, bool):
            return None, key + " must be of type " + kind.__name__
    if not 1 <= data["people"] <= 20:
        return None, "people must be between 1 and 20"
    return data, None

def get_booking(text: str, tries: int = 3):
    prompt = "Extract name, people (integer), date (YYYY-MM-DD) as JSON only: " + text
    for _ in range(tries):
        raw = call_model(prompt)
        data, error = check(raw)
        if data:
            return data
        prompt += "\nYour last answer: " + raw + "\nProblem: " + error + "\nTry again."
    raise ValueError("Model could not produce valid booking data")

print(get_booking("Table for four on 2 October for Asha, please."))