How to prevent a class to generate an object with an attribute used in an earlier instantiation, but not stop the code, in python

Question

ids = []
class Car:
    def __init__(self, id_no, *args):
        if id_no in ids:
            raise Exception('Duplicate id')
        self.car_data = [id_no, *args]
        ids.append(id_no)
car_1 = Car('WBA123', 'BMW', '530')
car_2 = Car('WBA123', 'Ford', 'Mustang')
car_3 = Car('WDB567', 'Mercedes', 'S400')

So, the car_2 should not be created instead show a message, but the car_3 should be created.

Answer 1

If you want the code not to stop, you should catch the exception using try-catch block. But since you need to do this for creating every instance of the class, it's better to make a car builder function for it. Something like following:

ids = []
class Car:
    def __init__(self, id_no, *args):
        if id_no in ids:
            raise Exception('Duplicate id')
        self.car_data = [id_no, *args]
        ids.append(id_no)


def build_car(*args):
    try:
        return Car(*args)
    except Exception as e:
        print(e)


car_1 = build_car('WBA123', 'BMW', '530')
car_2 = build_car('WBA123', 'Ford', 'Mustang')
car_3 = build_car('WDB567', 'Mercedes', 'S400')