I think Azure Pipeline fail is not related to my changes. is it possible to run tests again?

Close and reopen to rerun tests.

@facundobatista ,@remilapeyre , @serhiy-storchaka

as you know, argparse module tries to open the FileType object and if any error occurs it raises an exception. here's the code from Lib/argparse.py:

try:                                                                 
    return open(string, self._mode, self._bufsize, self._encoding, self._errors)
except OSError as e:
    args = {'filename': string, 'error': e}
    message = _("can't open '%(filename)s': %(error)s")
    raise ArgumentTypeError(message % args)

So when we run pickletools like this:

python -Wall Lib/pickletools.py file1 chertfile file2 

If chertfile doesn't exist, it raises the exception and we get ResourceWarning because file1 opened before and never closed.

Any idea? Should it be handled in argparse module?

Oh, mmm... so there are multiple exit/crashing points after argparse opened the file. It's impossible/too hard to cover them all outside argparse.

Probably the best way to fix this is in argparse itself, maybe it's as easy as using atexit.register(just_opened_file.close) there (which will behave correctly even if the file is manually closed before).

That way, also, this issue will not be solved only for pickle, but for everybody using argparse.

+1 from me to fix this in argparse, then.