code: def get_unknown_barcodes(self, lane_unknown_barcode):
          
          try:
              sorted_barcodes = OrderedDict(
                  sorted(
                      lane_unknown_barcode.items(),
                      key = operator.itemgetter(1),
                      reverse = True
                  )
              )
          except AttributeError:
              sorted_barcodes = None
          return sorted_barcodes
docs: Python 2.* dictionaries are not sorted.
          This function return an `OrderedDict` sorted by barcode count.