a bytes-like object is required, not str

[mangotuanzi]

Hello author, when I run train.py, it appears
File "LipReadingGUI-master/Training/lipnet/callbacks.py", line 86, in on_epoch_end
"{0:.5f}".format(stats['bleu'][0]), "{0:.5f}".format(stats['bleu'][1])])
TypeError: a bytes-like object is required, not 'str'
I am using python 3.6, how to solve this situation?