What does it mean for a private method to be only accessible from its own class in python?

Question

I read that Private class methods can't be called from outside their class.

If I have a Car class with a private method __reset_odometer()

can I say:

import Car
Car turboCar = Car();
turboCar.__reset_odometer();

__reset_odometer() is defined inside the Car class. turboCar is an instance of the Car class. So why does calling the method turboCar.__reset_odometer() result in an accesss error?

I guess 'outside the class' is a term that I am not understanding, b/c a turboCar to me is not outside the class Car

Answer 1

Calling turboCar.__reset_odometer() will raise an exception since, even though the method is being called on a Car object, it is still outside the class definition. Think of it this way: you aren't inside the class, writing definitions of methods when you instantiate turboCar = Car().

So you can still refer to __reset_odometer inside the class like so,

class Car(object):
    def __init__(self):
        self.__odometer = 88800
        self.__reset_odometer()  # <-- call double underscore function

    def __reset_odometer(self):
        self.__odometer = 0

    def read_odometer(self):
        return self.__odometer

And using turboCar works fine and the odometer has been reset,

>>> turboCar = Car()
>>> turboCar.read_odometer()
0

Of course, with Python there are no real private variables like in C++ and the like,

>>> turboCar._Car__odometer = 9999
>>> turboCar.read_odometer()
9999
>>> turboCar._Car__reset_odometer()
>>> turboCar.read_odometer()
0