Method __new__

example_code/item_062.py:77–82

(meta, name, bases, class_dict)

print("Example 2")
class ValidatePolygon(type):
    def __new__(meta, name, bases, class_dict):
        # Only validate subclasses of the Polygon class
        if bases:
            if class_dict["sides"] < 3:
                raise ValueError("Polygons need 3+ sides")
        return type.__new__(meta, name, bases, class_dict)

class Polygon(metaclass=ValidatePolygon):
    sides = None  # Must be specified by subclasses