design pattern quick reference template method pattern visitor pattern model-view-controller pattern publisher-subscriber pattern singleton singleton py class singletonobject(object)class __singletonobject()def __init__(self)self val none def __str__(self)return "{ ! { }format(selfself valthe rest of the class definition will follow hereas per the previous logging script instance none def __new__(cls)if not singletonobject instancesingletonobject instance singletonobject __singletonobject(return singletonobject instance def __getattr__(selfname)return getattr(self instancenamedef __setattr__(selfname)return setattr(self instancename