code: def as_xml_part(self, basename="/tmp/sitemap.xml", part_number=0):
          
          if (not self.requires_multifile()):
              raise ListBaseIndexError(
                  "Request for component sitemap for list with only %d entries when max_sitemap_entries is set to %s" %
                  (len(self), str(
                      self.max_sitemap_entries)))
          start = part_number * self.max_sitemap_entries
          if (start > len(self)):
              raise ListBaseIndexError(
                  "Request for component sitemap with part_number too high, would start at entry %d yet the list has only %d entries" %
                  (start, len(self)))
          stop = start + self.max_sitemap_entries
          if (stop > len(self)):
              stop = len(self)
          part = ListBase(itertools.islice(self.resources, start, stop))
          part.capability_name = self.capability_name
          part.default_capability()
          part.index = basename
          s = self.new_sitemap()
          return(s.resources_as_xml(part))
docs: Return a string of component sitemap number part_number.
  
          Used in the case of a large list that is split into component
          sitemaps.
  
          basename is used to create "index" links to the sitemapindex
  
          Q - what timestamp should be used?