You and the article author both didn't seem to read that link.

A single leading underscore is a convention to mark a variable as private.

A double leading underscore "name mangles" the variable (adds the class to the name of the variable) and has a specific use case for inheritance. They're class level private, which is probably not what you want.

    class Number:
        def __init__(self, n):
            self._number = n
            self.__number = n
    
    
    class NumberChild(Number):
        def one_higher(self):
            return self._number + 1
    
        def two_higher(self):
            return self.__number + 2
    
    
    number_child = NumberChild(10)
    number_child.one_higher()  # This works
    number_child.two_higher()  # This raises an Attribute Error