java23種設計模式之一，英文叫Builder Pattern。其核心思想是將一個“復雜對象的構建算法”與它的“部件及組裝方式”分離，使得構件算法和組裝方式可以獨立應對變化；復用同樣的構建算法可以創建不同的表示，不同的構建過程可以復用相同的部件組裝方式。

# coding: utf-8

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          # 考慮是示例，單位為秒


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        # 考慮是示例，單位為秒

    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 mozzarrella, 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        # 考慮是示例，單位為秒

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

    def add_sauce(self):
        print(‘adding the cre?me frai?che sauce to your creamy bacon‘)
        self.pizza.sauce = PizzaSauce.creme_fraiche
        time.sleep(STEP_DELAY)
        print(‘done with the cre?me frai?che 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      ## 實例屬性最好寫在__init__裏面，哪怕屬性不是在初始化時候綁定或者建立，也有寫個None，聲明一下屬性，否則直接在普通方法生成一個實例屬性，不符合pycharm的pep8。

    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)
    pizza = waiter.pizza
    print()
    print(‘Enjoy your {}!‘.format(pizza))

if __name__ == ‘__main__‘:
    main()

看代碼先從main函數看起，不是從上往下一行行看。

設計模式- 創建型模式， 建造者模式(2)