class DatabaseConnection:
    _instance = None

    def __new__(cls):
        if cls._instance is None:
            cls._instance = super().__new__(cls)
            cls._instance.connection = None
        return cls._instance

    def connect(self):
        if self.connection is None:
            self.connection = "Connected to Database"
        return self.connection

db1 = DatabaseConnection()
db2 = DatabaseConnection()
print(db1 is db2)  # True - Same instance

class Animal(ABC):
    @abstractmethod
    def make_sound(self): pass

class Dog(Animal):
    def make_sound(self): return "Woof!"

class Cat(Animal):
    def make_sound(self): return "Meow!"

class AnimalFactory:
    @staticmethod
    def create_animal(animal_type):
        if animal_type == "dog":
            return Dog()
        elif animal_type == "cat":
            return Cat()

dog = AnimalFactory.create_animal("dog")
print(dog.make_sound())  # Woof!

class PizzaBuilder:
    def __init__(self):
        self.pizza = Pizza()

    def set_size(self, size):
        self.pizza.size = size
        return self

    def add_topping(self, topping):
        self.pizza.toppings.append(topping)
        return self

    def build(self):
        return self.pizza

pizza = (PizzaBuilder()
         .set_size("Large")
         .add_topping("Pepperoni")
         .build())