How to Validate Dataclass Fields with Python Type Hints

from typing import Any, TypeVar, get_type_hints
from dataclasses import dataclass

T = TypeVar("T")

@dataclass
class User:
    name: str
    age: int
    email: str

def validate_fields(obj: Any) -> dict[str, bool]:
    """Check if object attributes match declared type hints."""
    hints = get_type_hints(obj.__class__)
    results = {}
    for field, expected_type in hints.items():
        value = getattr(obj, field, None)
        results[field] = isinstance(value, expected_type)
    return results

def print_validation_report(obj: Any) -> None:
    """Display validation results in a readable format."""
    report = validate_fields(obj)
    for field, is_valid in report.items():
        status = "✅ valid" if is_valid else "❌ invalid"
        print(f"{field}: {status}")

if __name__ == "__main__":
    # Test with correct data
    valid_user = User(name="Alice", age=30, email="alice@example.com")
    print("Valid user validation:")
    print_validation_report(valid_user)
    print()

    # Test with incorrect data type (age as string, should fail)
    bad_user = User(name="Bob", age="thirty", email="bob@example.com")
    print("Invalid user validation:")
    print_validation_report(bad_user)