def target_opacity(self, value):
        """
        Setter for **self.__target_opacity** 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("target_opacity", value)
            assert value >= 0, "'{0}' attribute: '{1}' need to be positive!".format("target_opacity", value)
            assert value <= 1, "'{0}' attribute: '{1}' need to be less or equal than '1'!".format(
                "target_opacity", value)
        self.__target_opacity = value