class Singleton(object):
def __new__(cls):
if not hasattr(cls,'_instance'):
cls._instance=super(Singleton,cls).__new__(cls)
cls.__instance = object.__new__(cls) #这样也可以
return cls._instance
a = Singleton()
b = Singleton()
c = Singleton()
print(a,id(a))
print(b,id(b))
print(c,id(c))
输出:
42443328
42443328
42443328
共享属性:创建实例时把所有实例的 __dict__指向同一个字典,这样它们具有相同的属性和方法.
class Borg(object):
_state = {}
def __new__(cls, *args, **kw):
ob = super(Borg, cls).__new__(cls, *args, **kw)
ob.__dict__ = cls._state
return ob
class MyClass2(Borg):
a = 1
b1 = MyClass2()
b2 = MyClass2()
b3 = MyClass2()
b1.a='萨菲的'
b2.a='萨菲02'
b1.a='萨菲03'
MyClass2.a = 333
print(id(b1),id(b2),id(b3))
print(b1.a,b3.a,b2.a)
print(id(b1.a),id(b2.a),id(b3.a))
输出:
42902024 42902080 42901688
萨菲03 萨菲03 萨菲03
167568080 167568080 167568080
def singleton(cls, *args, **kw):
instances = {}
def getinstance():
if cls not in instances:
instances[cls] = cls(*args, **kw)
return instances[cls]
return getinstance
@singleton
class MyClass:
a = 1
b1 = MyClass()
b2 = MyClass()
b3 = MyClass()
print(id(b1),id(b2),id(b3))
print(b1.a,b3.a,b2.a)
输出:
42712928 42712928 42712928
1 1 1
class Foo():
__v = None
@classmethod
def get_instance(cls):
if cls.__v:
print("true: 这是cls.__v",cls.__v)
return cls.__v
else:
print("false: 这是cls.__v", cls.__v)
cls.__v = Foo()
print("false_1: 这是cls.__v", cls.__v)
return cls.__v
obj = Foo.get_instance()
obj1 = Foo.get_instance()
obj2 = Foo.get_instance()
obj3 = Foo.get_instance()
print(obj,'哈哈',id(obj))
print(obj1,'哈哈',id(obj1))
print(obj2,'哈哈',id(obj2))
print(obj3,'哈哈',id(obj3))
输出:
false: 这是cls.__v None
false_1: 这是cls.__v
true: 这是cls.__v
true: 这是cls.__v
true: 这是cls.__v
哈哈 38798056
哈哈 38798056
哈哈 38798056
哈哈 38798056
单例默认:
'''
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'''
class Singleton(object):
def __new__(cls,*args,**kwargs):
if not hasattr(cls,'_instance'):
print('你好啊',)
cls._instance = super(Singleton,cls).__new__(cls)
print(cls._instance, '阿斯蒂芬01')
return cls._instance
print( '阿斯蒂芬')
print(cls._instance, '阿斯蒂芬02')
return cls._instance
a = Singleton()
print('这是a',id(a),a)
b = Singleton()
print('这是b',id(b),b)
输出:
你好啊
阿斯蒂芬01
这是a 42516208
阿斯蒂芬
阿斯蒂芬02
这是b 42516208
Original: https://www.cnblogs.com/djdjdj123/p/16627903.html
Author: Python探索牛
Title: Python教程：用__new__ 创建单例模式
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