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
优点：
缺点：
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))
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))
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))
- foo.py --> ins = Singleton() - bar.py --> from foo import ins
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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