Django设计模式

单例模式：

---

建造者模式：

示例：

from enum import Enum
import time

PizzaProgress = Enum('PizzaProgress', 'queued preparation baking ready')
PizzaDough = Enum('PizzaDough', 'thin thick')
PizzaSauce = Enum('PizzaSauce', 'tomato creme_fraiche')
PizzaTopping = Enum('PizzaTopping', 'mozzarella double_mozzarella bacon ham mushrooms red_onion oregano')

STEP_DELAY = 3

class Pizza:
    def __init__(self, name):
        self.name = name
        self.dough = None
        self.sauce = None
        self.topping = []

    def __str__(self):
        return self.name

    def prepare_dough(self, dough):
        self.dough = dough
        print('preparing the {} dough of your {}....'.format(self.dough.name, self))
        time.sleep(STEP_DELAY)
        print('done with the {} dough'.format(self.dough.name))

class MargaritaBuilder:
    def __init__(self):
        self.pizza = Pizza('margarita')
        self.progress = PizzaProgress.queued
        self.baking_time = 5

    def prepare_dough(self):
        self.progress = PizzaProgress.preparation
        self.pizza.prepare_dough(PizzaDough.thin)

    def add_sauce(self):
        print('adding the tomato sauce to your margarita....')
        self.pizza.sauce = PizzaSauce.tomato
        time.sleep(STEP_DELAY)
        print('done with the tomato sauce')

    def add_topping(self):
        print('adding the topping (double mozzarella,oregano) to your margarita')
        self.pizza.topping.append([i for i in (PizzaTopping.double_mozzarella, PizzaTopping.oregano)])
        time.sleep(STEP_DELAY)
        print('done with the topping (double mozzarella, oregano)')

    def bake(self):
        self.progress = PizzaProgress.baking
        print('baking your margarita for {} seconds'.format(self.baking_time))
        time.sleep(self.baking_time)
        self.progress = PizzaProgress.ready
        print('your margarita is ready')

class CreamyBaconBuilder:
    def __init__(self):
        self.pizza = Pizza('creamy bacon')
        self.progress = PizzaProgress.queued
        self.baking_time = 7

    def prepare_dough(self):
        self.progress = PizzaProgress.preparation
        self.pizza.prepare_dough(PizzaDough.thick)

    def add_sauce(self):
        print('adding the creme fraiche sauce to your creamy bacon')
        self.pizza.sauce = PizzaSauce.creme_fraiche
        time.sleep(STEP_DELAY)
        print('done with the creme fraiche sauce')

    def add_topping(self):
        print('adding the topping (mozzarella, bacon, ham, mushrooms,red onion, oregano) to your creamy bacon')
        self.pizza.topping.append([t for t in (
            PizzaTopping.mozzarella, PizzaTopping.bacon, PizzaTopping.ham, PizzaTopping.mushrooms,
            PizzaTopping.red_onion,
            PizzaTopping.oregano)])
        time.sleep(STEP_DELAY)
        print('done with the topping (mozzarella, bacon, ham,mushrooms, red onion, oregano)')

    def bake(self):
        self.progress = PizzaProgress.baking
        print('baking your creamy bacon for {} seconds'.format(self.baking_time))
        time.sleep(self.baking_time)
        self.progress = PizzaProgress.ready
        print('your creamy bacon is ready')

class Waiter:
    def __init__(self):
        self.builder = None

    def construct_pizza(self, builder):
        self.builder = builder
        [step() for step in (builder.prepare_dough, builder.add_sauce, builder.add_topping, builder.bake)]

    @property
    def pizza(self):
        return self.builder.pizza

def validate_style(builders):
    try:
        pizza_style = input('what pizza would you like, [m]argarita or [c]reamy bacon?')
        builder = builders[pizza_style]()
        valid_input = True
    except KeyError as err:
        print('Sorry, only margarita (key m) and creamy bacon (key c) are available')
        return (False, None)
    return (True, builder)

def main():
    builders = dict(m=MargaritaBuilder, c=CreamyBaconBuilder)
    valid_input = False
    while not valid_input:
        valid_input, builder = validate_style(builders)
    print()
    waiter = Waiter()
    # waiter.construct_pizza(builder)
    waiter.construct_pizza(builder)
    pizza = waiter.pizza
    print()
    print('Enjoy your {}!'.format(pizza))

if __name__ == '__main__':
    main()

结果一：

what pizza would you like, [m]argarita or [c]reamy bacon?c

preparing the thick dough of your creamy bacon....
done with the thick dough
adding the creme fraiche sauce to your creamy bacon
done with the creme fraiche sauce
adding the topping (mozzarella, bacon, ham, mushrooms,red onion, oregano) to your creamy bacon
done with the topping (mozzarella, bacon, ham,mushrooms, red onion, oregano)
baking your creamy bacon for 7 seconds
your creamy bacon is ready

Enjoy your creamy bacon!

结果二：

what pizza would you like, [m]argarita or [c]reamy bacon?m

preparing the thin dough of your margarita....
done with the thin dough
adding the tomato sauce to your margarita....
done with the tomato sauce
adding the topping (double mozzarella,oregano) to your margarita
done with the topping (double mozzarella, oregano)
baking your margarita for 5 seconds
your margarita is ready

Enjoy your margarita!

建造pizza示例