While writing the constructor for class A in Python, I calculate some of the class’s fields using function fun(). This function is never used outside the constructor of instances of this class.
In situations like these, I tend to write fun() so that it returns the desired values and then I assign these values in the initialization, like so:

class A:
    def __init__(self):
        self.x, self.y = self.fun(2)

    def fun(self, i: int) -> tuple[int, int]:
        return i**2, i**3

This to me seems clear in that the constructor clearly shows which fields are created.

A different approach would have these fields be assigned to inside fun(), like so:

class A:
    def __init__(self):
        self.fun(2)

    def fun(self, i: int):
        self.a = i**2
        self.b = i**3

I feel like this second method hinders readability because to see what fields are created or assigned to, I have to inspect fun(). However, maybe I’m missing something.

Is there any reason to prefer the second method over the first? Or are there any more reasons to prefer method one other than readability?

This question occurred to me while writing Python, but is not restricted to the Python language.