基本介绍
一个对象只允许被一次创建,一个类只能创建一个对象,并且提供一个全局访问点。
单例模式应该是应用最广泛,实现最简单的一种创建型模式。
特点:全局唯一,允许更改
优缺点
优点:
- 避免对资源的多重占用,如写入文件操作
- 节省内存
- 防止命名空间被污染
缺点:
- 没有接口,不能继承,与单一职责原则冲突,一个类应该只关心内部逻辑,而不关心外面怎么样来实例化
Python实现
方式1,元类实现:
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class MetaClass( type ):
def __call__( self , * args, * * kwargs):
"""
self : class Singleton
"""
if not hasattr ( self , "ins" ):
insObject = super (__class__, self ).__call__( * args, * * kwargs)
setattr ( self , "ins" , insObject)
return getattr ( self , "ins" )
class Singleton( object , metaclass = MetaClass):
pass
if __name__ = = "__main__" :
ins = Singleton()
print ( id (ins))
ins = Singleton()
print ( id (ins))
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方式2,继承实现:
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class ParentClass:
def __new__( cls , * args, * * kwargs) - > object :
"""
cls : class Singeton
"""
if not hasattr ( cls , "ins" ):
insObject = super (__class__, cls ).__new__( cls , * args, * * kwargs)
setattr ( cls , "ins" , insObject)
return getattr ( cls , "ins" )
class Singleton(ParentClass):
pass
if __name__ = = "__main__" :
ins = Singleton()
print ( id (ins))
ins = Singleton()
print ( id (ins))
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方式3,装饰器实现:
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def warpper(clsObject):
def inner( * args, * * kwargs):
if not hasattr (clsObject, "ins" ):
insObject = clsObject( * args, * * kwargs)
setattr (clsObject, "ins" , insObject)
return getattr (clsObject, "ins" )
return inner
@warpper
class Singleton:
pass
if __name__ = = "__main__" :
ins = Singleton()
print ( id (ins))
ins = Singleton()
print ( id (ins))
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方式4,模块实现:
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- foo.py - - > ins = Singleton()
- bar.py - - > from foo import ins
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方式5,@classmethod实现单例模式:
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class Singleton:
@classmethod
def getSingletonInstanceObject( cls , * args, * * kwargs):
if not hasattr ( cls , "ins" ):
insObject = cls ( * args, * * kwargs)
setattr ( cls , "ins" , insObject)
return getattr ( cls , "ins" )
if __name__ = = "__main__" :
ins = Singleton.getSingletonInstanceObject()
print ( id (ins))
ins = Singleton.getSingletonInstanceObject()
print ( id (ins))
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原文链接:https://www.cnblogs.com/Yunya-Cnblogs/p/14880267.html