A dataclass with validation

Python

__post_init__ runs after the generated constructor, which is where cheap invariants belong.

from dataclasses import dataclass, field

@dataclass(frozen=True, slots=True)
class Money:
    amount: int
    currency: str = 'GBP'

    def __post_init__(self):
        if self.amount < 0:
            raise ValueError('amount cannot be negative')

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Python dataclasses validation chris

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