for filename in os.listdir('.'):
    for file in filename:
       with open(os.path.join('.',file), 'r') as f:
            print(len(f))

FileNotFoundError                         Traceback (most recent call last)
<ipython-input-6-1702c8aca957> in <module>()
  1 for filename in os.listdir('.'):
  2     for file in filename:
----> 3         with open(os.path.join('.',file), 'r') as f:
  4             print(len(f))
  5

FileNotFoundError: [Errno 2] No such file or directory: './d'