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 und

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