Adds given variables to __variables attribute.

        :param \*args: Variables.
        :type \*args: \*
        :param \*\*kwargs: Variables : Values.
        :type \*\*kwargs: \*

def __add_variables(self, *args, **kwargs):
        """
        Adds given variables to __variables attribute.

        :param \*args: Variables.
        :type \*args: \*
        :param \*\*kwargs: Variables : Values.
        :type \*\*kwargs: \*
        """

        for variable in args:
            self.__variables[variable] = None
        self.__variables.update(kwargs)