ClassVar based dataclass instance counter

veget.py

from dataclasses import dataclass, field
from typing import ClassVar, List


@dataclass
class Veget:
    index: int = field(init=False)
    name: str
    price: float
    quantity: int
    MAX_COUNT: ClassVar[int] = 3
    _veget_index: ClassVar[List["Veget"]] = []

    def __post_init__(self):
        self.index = len(self._veget_index)
        if self.index >= self.MAX_COUNT:
            raise RuntimeError("Too many instances")
        self._veget_index.append(self)

print(Veget('tomato', 2.4, 5))
print(Veget('salad', 3.5, 2))
print(Veget('carot', 1.2, 7))
print(Veget('potato', 0.7, 3))