jsonpets.py

# Cats and Dogs

import sys
import json
from dataclasses import dataclass

@dataclass
class Animal:
    pass

@dataclass
class Pet(Animal):
    name: str

@dataclass
class Dog(Pet):
    breed: str
    leash_color: str

@dataclass
class Cat(Pet):
    pattern: str
    favorite_toy: str

def get_pets(raw: object) -> list[Cat | Dog]:
    match raw:
        case [*raw_pets]:  # List of pets
            return [get_pet(raw_pet) for raw_pet in raw_pets]
        case {**raw_pet}:  # Maybe a single pet
            return [get_pet(raw_pet)]
        case _:
            raise TypeError(f"Neither a pet nor a list of pets: {raw}")

def get_pet(raw_pet: object) -> Cat | Dog:
    match raw_pet:
        case {"type": "cat", "name": str(name), "pattern": str(pattern), "favorite_toy": str(toy)}:
            return Cat(name, pattern, toy)
        case {"type": "dog", "name": str(name), "breed": str(breed), "leash_color": str(leash)}:
            return Dog(name, breed, leash)
        case {"type": "cat" | "dog"}:
            raise TypeError(f"Malformed pet: {raw_pet}")
        case _:
            raise TypeError(f"Not a pet: {raw_pet}")

def main() -> None:
    raw = json.load(sys.stdin)
    for pet in get_pets(raw):
        print(pet)

if __name__ == "__main__":
    main()

# Example input:
#
# [
#   {"type": "dog", "name": "Sorry", "breed": "mutt", "leash_color": "black"},
#   {"type": "cat", "name": "Catelyn", "pattern": "tuxedo", "favorite_toy": "laser pointer"}
# ]
#
# Output:
#
# Dog(name='Sorry', breed='mutt', leash_color='black')
# Cat(name='Catelyn', pattern='tuxedo', favorite_toy='laser pointer')