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Factory pattern - Design Patterns

oop programming design-patterns

The factory pattern is a creational pattern that provides an interface for creating objects in a superclass, but allows subclasses to alter the type of objects that will be created.

Pattern type

Creational pattern

Intent

The factory pattern is a creational pattern that provides an interface for creating objects in a superclass, but allows subclasses to alter the type of objects that will be created.

Problem

You know the type of object you want to create, but you want to delegate the creation of the object to subclasses.

Pattern

The factory method pattern defines an interface for creating objects, but lets subclasses alter the type of objects that will be created. The factory method lets a class defer instantiation to subclasses.

Pizza
+name: string
+dough: string
+sauce: string
+toppings: string[]
+get_name() : string
+prepare() : void
+bake() : void
+cut() : void
+box() : void
CheesePizza
+name: string
+dough: string
+sauce: string
+toppings: string[]
PepperoniPizza
+name: string
+dough: string
+sauce: string
+toppings: string[]
ClamPizza
+name: string
+dough: string
+sauce: string
+toppings: string[]
VeggiePizza
+name: string
+dough: string
+sauce: string
+toppings: string[]
SimplePizzaFactory
+create_pizza(pizza_type: string) : Pizza
PizzaStore
-factory: SimplePizzaFactory
+order_pizza(pizza_type: string) : Pizza
  • list here

Code example

from abc import ABC, abstractmethod
 
class Pizza(ABC):
    def __init__(self):
        self.name = None
        self.dough = None
        self.sauce = None
        self.toppings = []
 
    def get_name(self):
        return self.name
 
    def prepare(self):
        print("Preparing " + self.name)
        print("Tossing dough...")
        print("Adding sauce...")
        print("Adding toppings: " + ", ".join(self.toppings))
 
    def bake(self):
        print("Baking " + self.name)
 
    def cut(self):
        print("Cutting " + self.name)
 
    def box(self):
        print("Boxing " + self.name)
 
 
class CheesePizza(Pizza):
    def __init__(self):
        self.name = "Cheese Pizza"
        self.dough = "Regular Crust"
        self.sauce = "Marinara Pizza Sauce"
        self.toppings = []
        self.toppings.append("Fresh Mozzarella")
        self.toppings.append("Parmesan")
 
 
class PepperoniPizza(Pizza):
    def __init__(self):
        self.name = "Pepperoni Pizza"
        self.dough = "Crust"
        self.sauce = "Marinara sauce"
        self.toppings = []
        self.toppings.append("Sliced Pepperoni")
        self.toppings.append("Sliced Onion")
        self.toppings.append("Grated parmesan cheese")
 
class ClamPizza(Pizza):
    def __init__(self):
        self.name = "Clam Pizza"
        self.dough = "Regular crust"
        self.sauce = "Tomato sauce"
        self.toppings = []
        self.toppings.append("Fresh clams")
        self.toppings.append("Garlic")
        self.toppings.append("Grated parmesan cheese")
 
class VeggiePizza(Pizza):
    def __init__(self):
        self.name = "Veggie Pizza"
        self.dough = "Crust"
        self.sauce = "Marinara sauce"
        self.toppings = []
        self.toppings.append("Shredded mozzarella")
        self.toppings.append("Grated parmesan")
        self.toppings.append("Diced onion")
        self.toppings.append("Sliced mushrooms")
 
class PizzaStore:
    def __init__(self, factory):
        self.factory = factory
 
    @abstractmethod
    def order_pizza(self, pizza_type: str):
        pizza = self.factory.create_pizza(pizza_type)
 
        pizza.prepare()
        pizza.bake()
        pizza.cut()
        pizza.box()
 
        return pizza
 
class SimplePizzaFactory:
    def create_pizza(self, pizza_type: str):
        pizza = None
 
        if pizza_type == 'cheese':
            pizza = CheesePizza()
        elif pizza_type == 'pepperoni':
            pizza = PepperoniPizza()
        elif pizza_type == 'pepperoni':
            pizza = PepperoniPizza()
        elif pizza_type == 'clam':
            pizza = ClamPizza()
        elif pizza_type == 'veggie':
            pizza = VeggiePizza()
        else:
            raise ValueError(f'Invalid pizza type: {pizza_type}')
 
        return pizza
 
 
factory = SimplePizzaFactory()
store = PizzaStore(factory)
 
pizza = store.order_pizza('cheese')
print(f"Ordered a {pizza.get_name()}\n")
 
pizza = store.order_pizza('pepperoni')
print(f"Ordered a {pizza.get_name()}\n")
 
pizza = store.order_pizza('clam')
print(f"Ordered a {pizza.get_name()}\n")
 
pizza = store.order_pizza('veggie')
print(f"Ordered a {pizza.get_name()}\n")

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