Metaclasses Python

metaclass.py

# Rarely used, metaclasses can be used for validation of other classes

class ValidatePolygon(type):
    
    def __new__(meta, name, bases, class_dict):
        # Don’t validate the abstract Polygon class
        if bases != (object,):
            if class_dict[‘sides’] < 3:
                raise ValueError(‘Polygons need 3+ sides’)
        return type.__new__(meta, name, bases, class_dict)
    
class Polygon(object, metaclass=ValidatePolygon):
    sides = None  # Specified by subclasses
    
    @classmethod
    def interior_angles(cls):
        return (cls.sides - 2) * 180

class Triangle(Polygon):
    sides = 3