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OOP & classes

Classes, instances, methods, dataclasses, and object-oriented design in Python.

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OOP & classes easy

Validate dataclass fields with __post_init__ in Python

Add custom validation to a Python dataclass inside __post_init__, raising ValueError or TypeError for invalid field values.

dataclasses validation post-init
Python 
from dataclasses import dataclass, field
from typing import Optional


@dataclass
class Product:
    name: str
    price: float
    quantity: int = 1
    category: Optional[str] = None

    def __post_init__(self):
        if not self.name or not isinstance(self.name, str):
            raise ValueError("name must be a…
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