关于python的单实例模式
单实例模式一直是常用的设计模式,对于python的单实例模式,其实其本身就有实现
里面说到module,module只会初始化一次,天然的singleton。这是最为python的解决方案。将你所需要的属性和方法,直接暴露在模块中变成模块的全局变量和方法即可。
另外,如果真的要使用代码进行singleton,下面给出几个代码
# Singleton/ClassVariableSingleton.py
class SingleTone(object):
__instance = None
def __new__(cls, val):
if SingleTone.__instance is None:
SingleTone.__instance = object.__new__(cls)
SingleTone.__instance.val = val
return SingleTone.__instance
# Singleton/SingletonDecorator.py class SingletonDecorator: def __init__(self,klass): self.klass = klass self.instance = None def __call__(self,*args,**kwds): if self.instance == None: self.instance = self.klass(*args,**kwds) return self.instance class foo: pass foo = SingletonDecorator(foo) x=foo() y=foo() z=foo() x.val = 'sausage' y.val = 'eggs' z.val = 'spam' print(x.val) print(y.val) print(z.val) print(x is y is z)
# Singleton/SingletonMetaClass.py
class SingletonMetaClass(type):
def __init__(cls,name,bases,dict):
super(SingletonMetaClass,cls)\
.__init__(name,bases,dict)
original_new = cls.__new__
def my_new(cls,*args,**kwds):
if cls.instance == None:
cls.instance = \
original_new(cls,*args,**kwds)
return cls.instance
cls.instance = None
cls.__new__ = staticmethod(my_new)
class bar(object):
__metaclass__ = SingletonMetaClass
def __init__(self,val):
self.val = val
def __str__(self):
return `self` + self.val
x=bar('sausage')
y=bar('eggs')
z=bar('spam')
print(x)
print(y)
print(z)
print(x is y is z)