customers.py

class RegularCustomer:

    def __init__(self, name, item, price, quantity):
        self.name = name
        self.item = item
        self.price = price
        self.quantity = quantity

    def discount(self):
        return self.price * 0.3

    def final(self):
        return (self.price - self.discount()) * self.quantity


class OccasionalCustomer(RegularCustomer):
    def __init__(self, name, item, price, quantity):
        super().__init__(name, item, price, quantity)

    def discount(self):
        return self.price * 0.1


# common interface
def cal_discount(object):
    z = object.discount()
    print(f'{object.name}\'s discount will be {z}')
    print(f'{object.final()} is your final price')


# instantiating objects for the two classes

cus_1 = RegularCustomer('Atufa', 'shoes', 600, 1)
cus_2 = OccasionalCustomer('Shireen', 'shoes', 600, 1)

# passing the objects to common interface
print(cal_discount(cus_1))
print(cal_discount(cus_2))