code: def group_files_by_size_simple(fileslist, nbgroups):  # pragma: no cover
      
      ford = sorted(fileslist.iteritems(), key=lambda x: x[1], reverse=True)
      ford = [[x[0]] for x in ford]
      return [group for group in grouper(nbgroups, ford)]
docs: Simple and fast files grouping strategy: just order by size, and group files n-by-n, so that files with the closest sizes are grouped together.
      In this strategy, there is only one file per subgroup, and thus there will often be remaining space left because there is no filling strategy here, but it's very fast.