code: def _build_sliced_filepath(filename, slice_count):
      
      root = os.path.splitext(filename)[0]
      ext = os.path.splitext(filename)[1]
      new_filepath = ''.join((root, str(slice_count), ext))
      return _build_filepath_for_phantomcss(new_filepath)
docs: append slice_count to the end of a filename