Setter for **self.__pattern** attribute.

        :param value: Attribute value.
        :type value: unicode

def pattern(self, value):
        """
        Setter for **self.__pattern** attribute.

        :param value: Attribute value.
        :type value: unicode
        """

        if value is not None:
            assert type(value) in (unicode, QString), \
                "'{0}' attribute: '{1}' type is not 'unicode' or 'QString'!".format("pattern", value)
        self.__pattern = value