python单例模式实现
作用
首先单例模式简单理解全局公用一个实例，在不同的模块引入实例化只会实例化一次，不会造成资源的浪费，很大的节省了内存空间。
实现方式
这里列举常见的4种基于python的实现方式
1.使用函数装饰器实现单例
def singleton(cls):
_instance = {}
def inner():
if cls not in _instance:
_instance[cls] = cls()
return _instance[cls]
return inner
@singleton
class Cls(object):
def __init__(self):
pass
cls1 = Cls()
cls2 = Cls()
print(id(cls1) == id(cls2))
2.使用类装饰器实现单例
class Singleton(object):
def __init__(self, cls):
self._cls = cls
self._instance = {}
def __call__(self):
if self._cls not in self._instance:
self._instance[self._cls] = self._cls()
return self._instance[self._cls]
@Singleton
class Cls2(object):
def __init__(self):
pass
cls1 = Cls2()
cls2 = Cls2()
print(id(cls1) == id(cls2))
3.使用 new 关键字实现单例模式
class Single(object):
_instance = None
def __new__(cls, *args, **kw):
if cls._instance is None:
cls._instance = object.__new__(cls)
return cls._instance
def __init__(self):
pass
single1 = Single()
single2 = Single()
print(id(single1) == id(single2))
4.使用 metaclass 实现单例模式
class Singleton(type):
_instances = {}
def __call__(cls, *args, **kwargs):
if cls not in cls._instances:
cls._instances[cls] = super(Singleton, cls).__call__(*args, **kwargs)
return cls._instances[cls]
class Cls4(metaclass=Singleton):
pass
cls1 = Cls4()
cls2 = Cls4()
print(id(cls1) == id(cls2))