Can access class private variable?

[Michael]

Hi,

Am new to Python3 (previously Java)
Below I make a class, instantiate it, and then do 2 things I don't understand (see comments)

Appreciate some help - Michael

class HWClass:

    def __init__(self): 
        self.__classvar = 3 #private
        self.printHW()

    def printHW(self): 
        print("Hello World")

hw = HWClass()  #Instantiation
hw.__classvar = 4  #This suggests I change a private class variable? It doesn't actually change, but the text suggests it does, which is error-prone
hw.varxxxx = 9 #How can I use a variable on this class object that is not defined in the class?