python - 是否可以声明一个类变量，该变量将产生其他两个类变量的总和

Question

class my_class(object):
    def __init__(self):
        self.ref        = 0
        self.ask        = 0
        self.added      = self.ref + self.ask 

inst = my_class()
inst.ref   = 5
inst.ask   = 7
print(inst.ref + inst.ask)
print(inst.added)

我希望 print(inst.added) 返回 12 但它返回 0

Answer 1

最简单的方法是使 added 成为一个方法并调用它:

>>> class A:
...    def __init__(self):
...       self.ref = 0
...       self.ask = 0
...    def added(self):
...       return self.ref + self.ask
...
>>> a = A()
>>> a.ref = 5
>>> a.ask = 7
>>> a.added()
12
>>>

或者您可以使 added 成为一个属性，这样您就可以像访问数据属性而不是方法一样访问它:

>>> class A:
...    def __init__(self):
...       self.ref = 0
...       self.ask = 0
...    @property
...    def added(self):
...       return self.ref + self.ask
...
>>> a = A()
>>> a.ref = 5
>>> a.ask = 7
>>> a.added
12
>>>