【Python学习之八】设计模式和异常

class Singleton(object):
    __instance=None
    __first_init=False
    
    def __new__(cls,name,age):
        if not cls.__instance:
            cls.__instance=object.__new__(cls);
        return cls.__instance
    def __init__(self,name,age):
        if not self.__first_init:
            self.name=name
            self.age=age
            Singleton.__first_init=True

a=Singleton(‘bin‘,18)
b=Singleton(‘bin‘,8)
#只有一个实例
print(id(a))
print(id(b))
#只初始化一次
print(a.age)
print(b.age)
#修改属性
a.age=19
print(b.age)

class Person(object):
    def __init__(self,name):
        self.name=name
    def work(self,type):
        print(‘%s开始工作了‘%self.name)
        ax=Factory.create_axe(self, type)
        ax.cut_tree()
        
class Axe(object):
    def cut_tree(self):
        print(‘开始砍树了‘)
class StoneAxe(Axe):
    def cut_tree(self):
        print(‘石斧砍树‘)
class SteelAxe(Axe):
    def cut_tree(self):
        print("使用钢斧头砍树")
class WaterAxe(Axe):
    def cut_tree(self):
        print("使用水砍树")    
    
class Factory(object):
    @staticmethod
    def create_axe(self,ax_type):
        if ax_type==‘stone‘:
            return StoneAxe()
        elif ax_type==‘steel‘:
            return SteelAxe()
        elif ax_type==‘water‘:
            return WaterAxe()
        else:
            print(‘类型错误‘)
p=Person(‘光头强‘)#光头强开始工作了
p.work(‘steel‘)#使用钢斧头砍树