Validate dictionary data with sets in Python

def validate_data(data, required_keys, allowed_values=None):
    """
    Validate a dictionary against required keys and optional allowed value sets.
    Returns a list of validation errors (empty list if valid).
    """
    errors = []
    
    # Check for missing required keys
    missing = set(required_keys) - set(data.keys())
    if missing:
        errors.append(f"Missing keys: {sorted(missing)}")
    
    # Check for unexpected keys
    unexpected = set(data.keys()) - set(required_keys)
    if unexpected:
        errors.append(f"Unexpected keys: {sorted(unexpected)}")
    
    # Check allowed values if provided
    if allowed_values:
        for key, valid_set in allowed_values.items():
            if key in data and data[key] not in valid_set:
                errors.append(
                    f"Invalid value for '{key}': {data[key]!r}. "
                    f"Allowed: {sorted(valid_set)}"
                )
    
    return errors

if __name__ == "__main__":
    # Example usage for validation
    person = {"name": "Alice", "age": 30, "status": "active"}
    required = {"name", "age", "status"}
    allowed = {"status": {"active", "inactive"}}
    
    errors = validate_data(person, required, allowed)
    print("Errors:", errors if errors else "None — data is valid")
    
    # Test with invalid data
    bad_person = {"name": "Bob", "status": "unknown"}
    errors = validate_data(bad_person, required, allowed)
    print("Errors:", errors if errors else "None — data is valid")