day26 面向对象 单例模式总结

如果是在python2中,就需要手动继承object,

 基于__new__方法

        基于__new__方法
        class Foo(object):
            def __new__(cls,*args,**kwargs):
                if not hasattr(cls,'_instance'):
                    cls._instance=super(Foo,cls).__new__(cls,*args,**kwargs)
                return cls._instance     

 基于装饰器方法

def foo(cls,*args,**kwargs):
            dic={}
            def _foo():
                if cls not in dic:
                    dic[cls]=cls(*args,**kwargs)
                return dic[cls]
            return _foo
            
        @foo
        class MyClass(object):
            x=2
            def __init__(self,x=1)
                self.x=x

基于元类metaclass实现

class Singleton(type):
            def __init__(cls,*args,**kwargs):
                super(Singleton,cls).__init__(name,bases,dict)
                cls._instance=None
            def __call__(cls,*args,**kwargs):
                if cls._instance is None:
                    cls._instance=super(Singleton,cls).__call__(*args,**kwargs)
                return cls._instance
                
        class MyClass(object):
            __metaclass__=Singleton

知识点总结，封装，静态变量变成私有变量