If TextIOWrapper constructor fails in tokenize.open(), the open binary file is not closed and a ResourceWarning is emited.

Try attached patch:

$ python3 -Wd ~/tokenize_open_bug.py
tokenize.open failed: unknown encoding for 'test.py': xxx
/home/haypo/tokenize_open_bug.py:13: ResourceWarning: unclosed file <_io.BufferedReader name='test.py'>
  print("tokenize.open failed: %s" % err)

The fix is quite simple: add "try: ... except: buffer.close(); raise". If someone wants to fix this issue, an unit test must be added, test based on my script and ensures that the buffer is closed (ex: mock tokenize._builtin_open and checks that close() was called).