目录
1. 单例模式
1.1 什么是单例模式
- 单例模式就是基于某种方法实例化多次得到的示例是同一个
class Foo():
def __init__(self,name, age):
self.name = name
self.age = age
f1 = Foo('hades',13)
print(f1)
f2 = Foo('hades',13)
print(f2)
f3 = Foo('hades',13)
print(f3)
<__main__.Foo object at 0x0000023CB56AD518>
<__main__.Foo object at 0x0000023CB56AD550>
<__main__.Foo object at 0x0000023CB5688048>
上面演示的就不属于单例模式，虽然看起来实例化对象一摸一样，但从内存地址就能看出，其实都是单独的对象
1.2 为什么用单例模式
-
当实例化多次得到的对象存放的属性都是一样的时候，我们就没必要去占用更多的内存空间，实例化对象指向同一个内存
-
最终目的就是省内存
1.3 单例模式三种方式
1.3.1 使用类内部绑定方法特性，定义静态方法
NAME = 'hades'
AGE = 27
class People:
__instance = None
def __init__(self,name,age):
self.name = name
self.age = age
@classmethod
def from_conf(cls):
if cls.__instance:
return cls.__instance
cls.__instance = People.__init__(cls,NAME,AGE)
return cls.__instance
p1 = People.from_conf()
p2 = People.from_conf()
print(p1==p2)
True
1.3.2 利用装饰器实现单例模式
NAME = 'hades'
AGE = 27
def deco(cls):
cls.__instance = cls(NAME,AGE)
def wrapper(*args,**kwargs):
if len(args) == 0 and len(kwargs) == 0:
return cls.__instance
res = cls(*args,**kwargs)
return res
return wrapper
@deco
class People():
def __init__(self,name,age):
self.name = name
self.age = age
p1 = People()
p2 = People()
p3 = People('bonnie',16)
print(p1 == p2)
print(p1 == p3)
True
False
1.3.3 利用元类实现单例模式
NAME = 'hades'
AGE = 27
class Mymeta(type):
def __init__(self, class_name, class_bases, class_dict):
super().__init__(class_name, class_bases, class_dict)
self.__instance = self(NAME, AGE)
def __call__(self, *args, **kwargs):
if len(args) == 0 and len(kwargs) == 0:
return self.__instance
obj = self.__new__(self)
self.__init__(obj, *args, **kwargs)
return obj
class People(metaclass=Mymeta):
def __init__(self,name,age):
self.name = name
self.age = age
p1 = People()
p2 = People()
p3 = People('bonnie',16)
print(p1 == p2)
print(p1 == p3)
True
False