When to store things as part of an instance vs returning them?

Question

I was just wondering when to store things as part of a class instance versus when to use a method to return things. For example, which of the following would be better:

class MClass():

    def __init__(self):
        self.x = self.get_x()
        self.get_y()
        self.z = None
        self.get_z()

    def get_x(self):
        return 2

    def get_y(self):
        self.y = 5 * self.x

    def get_z(self):
        return self.get_x() * self.x 

What are the conventions regarding this sort of thing and when should I assign things to self and when should I return values? Is this essentially a public/private sort of distinction?

Answer 1

You can use the @property decorator:

class MClass():

    def __init__(self):
        self.x = 2

    @property
    def y(self):
        return 5 * self.x

    #here a plus method for the setter
    @y.setter
    def y(self,value):
        self.x = y/5   

    @property    
    def z(self):
        return self.x * self.x 

It's a good way of organizing yours accessors