TypeError: Can't mix strings and bytes in path components

#問題

with open('LICENSE.txt', 'rb') as f:
  s = [os.path.join('a', line.strip()) for line in f]

#error
#TypeError: Can't mix strings and bytes in path components

#解決

with open('LICENSE.txt', 'rb') as f:
  s = [os.path.join(b'a', line.strip()) for line in f]

#原因
バイト列とstrを混同させていた。バイト列にそろえた。