如何在Python中从基类访问派生类的实例变量

Question

I have the next code in Python:

class Base_class():
    def __init__(self):
        pass

    # this is the method where I need help
    def compress(variable?,index?):
        somecode()

class Derived_class_1():   
    def __init__(self,somelist):
        self.A = []
        self.B = []
        for item in somelist:
            if item == 1:
                self.A.append([1,0])
                self.B.append([0,1])
            else:
                self.A.append([1,0])
                self.B.append([1,0])

class Derived_class_2(): 
    def __init__(self,somelist):
        self.A = []
        self.B = []
        for item in somelist:
            if item == 1:
                self.A.append([1,0])
                self.B.append([1,0])
            else:
                self.A.append([1,0])
                self.B.append([0,1])

I need to be able in the compress method from the base class to access each of the instance values and return a list of one dimension based on the index given that the instance variable has two possible values for each element in the list. Do I need to make the compress method a class one? And if it is the case, how can I make it possible?

Answer 1

2 problems with your code I see.

• Derrived classes don't inherit from Base_class
• self is missing from compress

Changes:

class Base_class():
    # ...
    def compress(self, variable, index):
        print(self.A)
        print(self.B)

class Derived_class_1(Base_class):
    # ...

class Derived_class_2(Base_class):
    # ...

Then to test

>>> x = Derived_class_1([1, 2])
>>> x.compress(5, 6)
[[1, 0], [1, 0]]
[[0, 1], [1, 0]]

>>> y = Derived_class_2([1, 2])
>>> y.compress(5, 6)
[[1, 0], [1, 0]]
[[1, 0], [0, 1]]