Name (file or URI) for one component sitemap.

        Works for both filenames and URIs because manipulates only the end
        of the string.

        Abstracting this into a function that starts from the basename to get
        prefix and suffix each time seems a bit wasteful but perhaps not worth
        worrying about. Allows same code to be used for the write() and
        as_xml_index() cases.

def part_name(self, basename='/tmp/sitemap.xml', part_number=0):
        """Name (file or URI) for one component sitemap.

        Works for both filenames and URIs because manipulates only the end
        of the string.

        Abstracting this into a function that starts from the basename to get
        prefix and suffix each time seems a bit wasteful but perhaps not worth
        worrying about. Allows same code to be used for the write() and
        as_xml_index() cases.
        """
        # Work out how to name the sitemaps, attempt to add %05d before
        # ".xml$", else append
        sitemap_prefix = basename
        sitemap_suffix = '.xml'
        if (basename[-4:] == '.xml'):
            sitemap_prefix = basename[:-4]
        return(sitemap_prefix + ("%05d" % (part_number)) + sitemap_suffix)