设计模式之开闭原则

面向对象程序应该 对扩展开放，对更改封闭。
如果更改代码，要重新编译，重新测试，重新部署，会附带很多其他操作。
python可以使用鸭子模式，进行多态调用。
如下， a和b可以独立变化，不影响以下代码的稳定：

self.x = a
self.x.duck()
 
self.x = b
self.x.duck()

正常模式：

# pay_money.py
#!/usr/bin/env python
# ~*~ coding: utf-8 ~*~
 
def get_result(type, money):
    """商场促销"""
    result = money
    if money > 10000:
        if type == "UserType.SILVER_VIP":
            print("白银会员 优惠50元")
            result = money - 50
        elif type == "UserType.GOLD_VIP":
            print("黄金会员 8折")
            result = money * 0.8
 
        elif type == "UserType.PLATINUM_VIP":
            print("白金会员 优惠50元，再打7折")
            result = money * 0.7 - 50
        else:
            print("普通会员 不打折")
            result = money
 
    return result

策略模式

class CashSuper(object):
    """收款抽象类"""
 
    def pay_money(self,money):
        pass
 
 
class SilverUser(CashSuper):
    """策略1:白银会员收费模式"""
 
    def __init__(self, discount_money=50):
        self.discount_money = discount_money
 
    def pay_money(self,money):
        return money - self.discount_money
 
class GoldUser(CashSuper):
    """策略2: 黄金会员收费模式"""
    def __init__(self,discount=0.8):
        self.discount = discount
 
    def pay_money(self,money):
        return money* self.discount
 
class PlatinumUser(CashSuper):
    """策略3: 白金会员收费模式"""
 
    def __init__(self,discount_money=50,discount=0.7):
        self.discount_money = discount_money
        self.discount = discount
 
    def pay_money(self,money):
        if money >= self.discount_money:
            return money* self.discount - self.discount_money
        return money
 
class NormalUser(CashSuper):
    """策略4: 正常会员不打折"""
 
    def pay_money(self,money):
        return money
 
 
class Context(object):
    """具体实现的策略类"""
 
    def __init__(self,cash_super):
        """初始化:将策略类传递进去作为属性"""
        self.cash_super = cash_super
 
    def get_result(self,money):
        return self.cash_super.pay_money(money)
 
 
def main(money, user_type):
    """程序入口"""
	if money  < 1000:
		return money
    if user_type == "UserType.SILVER_VIP":
        strategy = Context(SilverUser())
    elif user_type == "UserType.GOLD_VIP":
        strategy = Context(GoldUser())
    elif user_type == "UserType.PLATINUM_VIP":
        strategy = Context(PlatinumUser())
    else:
        strategy = Context(NormalUser())
 
    return strategy.get_result(money)