方法中的Python类属性

Question

Consider the following code, I want you to explain why the code doesn't work because I have seen others to assign the class attributes outside __init__ and call the attributes in one method from another, what is wrong with mine. The following three prints all result error saying the class has no attributes whatsoever.

class Person(object):
    def __init__(self, age, height):
        self.age = age
        self.height = height

    def weight_kg(self):
        self.weight = 60

    def ratio_kg2height(self):
        self.ratio = self.weight / self.height
        return self.ratio


mike = Person(23, 170)
print mike.weight
print mike.ratio_kg2height()
print mike.ratio

Answer 1

You are not defining the weight attribute in the __init__ method, since you dont call weight_kg method before accesing the attribute it is not available.

You have some options here, the basic one is to initialize it first, you can simply call your methods in the __init__ method:

class Person(object):
    def __init__(self, age, height):
        self.age = age
        self.height = height
        self.weight_kg()
        self.ratio_kg2height()

    ...

Here you have a live example