Python 调用具有来自另一个类方法的单个实例的 class 的一个方法

Question

I am new to using python and not sure how can I call one method of a class (another_functionality from class Service) whose instance has to be created only once during a workflow from another class (ServiceCalculator), if I use self.another_functionality(param1 ,param2) 它抛出错误，我不能创建另一个 class 服务实例，因为要求是只使用一个实例。

-----------------------
MainProcess.py
------------------------
Creating Service() object
------------------------
class Service:
    def __init__(self):
        self.service_cal = ServiceCalculator()
        self.service_producer = ServiceProducer()

    def process_calling(self, param1, param2):
        self.service_cal.process_service(param1, param2)

    def another_functionality(self, a, b):
       // Another functionality
       self.service_producer.send()


class ServiceCalculator:
     def process_service(self, param1, param2):
         if(param1=True):
           self.another_functionality(param1,param2)

Answer 1

您正在寻找的是 singleton 模式。 无论您调用多少次，class 始终只有一个实例。

class Singleton(object):
        def __new__(cls, *args, **kwds):
            it = cls.__dict__.get("__it__")
            if it is not None:
                return it
            cls.__it__ = it = object.__new__(cls)
            it.init(*args, **kwds)
            return it
        def init(self, *args, **kwds):
            pass

https://www.python.org/download/releases/2.2/descrintro/#__new_