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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.