Сериализация datetime и Decimal в JSON с явным контрактом на Python

import json
from datetime import datetime, timezone
from decimal import Decimal, InvalidOperation

def contract_encoder(obj):
    if isinstance(obj, datetime):
        if obj.tzinfo is None or obj.utcoffset() is None:
            raise TypeError("Timezone-aware datetime required")
        return obj.isoformat()
    if isinstance(obj, Decimal):
        if not obj.is_finite():
            raise TypeError("Finite Decimal required")
        return str(obj)
    raise TypeError("Unsupported custom value")

def reconstruct_data(data):
    if not isinstance(data, dict):
        raise ValueError("Object required")
    if not all(isinstance(data.get(key), str) for key in ("timestamp", "amount")):
        raise ValueError("timestamp and amount must be strings")
    timestamp = datetime.fromisoformat(data["timestamp"])
    if timestamp.tzinfo is None or timestamp.utcoffset() is None:
        raise ValueError("Timezone-aware timestamp required")
    amount = Decimal(data["amount"])
    if not amount.is_finite():
        raise ValueError("Finite amount required")
    return {"timestamp": timestamp, "amount": amount}

data = {"timestamp": datetime(2026, 9, 29, 12, 0, tzinfo=timezone.utc),
        "amount": Decimal("12.30")}
encoded = json.dumps(data, default=contract_encoder, allow_nan=False)
print(encoded)
restored = reconstruct_data(json.loads(encoded))
print(restored["timestamp"].isoformat(), str(restored["amount"]))