Setter for **self.__fade_speed** attribute.

        :param value: Attribute value.
        :type value: float

def fade_speed(self, value):
        """
        Setter for **self.__fade_speed** attribute.

        :param value: Attribute value.
        :type value: float
        """

        if value is not None:
            assert type(value) is float, "'{0}' attribute: '{1}' type is not 'float'!".format("fade_speed", value)
            assert value >= 0, "'{0}' attribute: '{1}' need to be exactly positive!".format("fade_speed", value)
        self.__fade_speed = value