Setter for **self.__categories** attribute.

        :param value: Attribute value.
        :type value: dict

def categories(self, value):
        """
        Setter for **self.__categories** attribute.

        :param value: Attribute value.
        :type value: dict
        """

        if value is not None:
            assert type(value) is dict, "'{0}' attribute: '{1}' type is not 'dict'!".format("categories", value)
            for key, element in value.iteritems():
                assert type(key) is dict, "'{0}' attribute: '{1}' type is not 'dict'!".format("categories", key)
                assert type(element) is list, "'{0}' attribute: '{1}' type is not 'list'!".format(
                    "categories", element)
        self.__categories = value