When one uses a file object returned by `FileType.__call__` as a context manager, `sys.stdin`'s or `sys.stdout`'s `__exit__` will be triggered upon exit of the context, in turn calling their `close` method.

Perhaps the issue is that `sys.stdin` and `sys.stdout` have poor `__exit__` methods, but my proposal (and it's not a particularly clean one) is to override the file object's `__exit__` if it happens to be either `sys.stdin` or `sys.stdout` to simply return True when called.

Hmm, not sure why I thought I needed `inline code formatting`. It's all monospace anyway!

Anyway, I'm thinking that adding this somewhere in argparse.py:

class _WrappedIO(object):
    def __init__(self, fileobj):
        self._file = fileobj

    def __exit__(tp, val, tb):
        return True

    def __getattr__(self, name):
        return self._file.__gettattr__(name)

and then applying the attached patch *may* fix this.

Perhaps instead it could return an io object built from the file descriptor with closefd=False.

Related issues are:

http://bugs.python.org/issue13824 - argparse.FileType opens a file and never closes it
http://bugs.python.org/issue14156 - argparse.FileType for '-' doesn't work for a mode of 'rb'

As discussed earlier FileType was meant as a convenience for small scripting applications, ones that don't try to close the file before exiting.

But now we are encouraged to open files in a context that guarantees closure.  In 13824 I proposed a 'FileContext', and included a dummy context like this handle stdin/out.

But I think the closefd=False approach raised in 14156 and David is probably the better way to go.

I think the main thing that is lacking is a testing mechanism.