Preferred method to get a class variable inside a class in Python. Custom method vs self

Question

I was wondering if there is a preferred method to refer to a value from within a class.

For example in the following code:

class Coordinate(object):

    def __init__(self, x):
        self.x = x

    def getX(self):
        return(self.x)

    def transform(self, dx):
        return self.x - dx

When I want to use x somewhere in another method of the Coordinate class, for example in the transform method, what is the preferred way to refer to x? Is it with self.x or self.getX(), such that transform becomes:

    def transform(self, dx):
        return self.getX() - dx

I understood that using getX() is preferred when trying to get the value x from outside the class. Thus:

>>> c = Coordinate(13)
>>> print(c.getX()) # Preferred method
13
>>> print(c.x) 
13