If an argument of '-' is handled by argparse.FileType, it defaults to sys.stdin. However a mode of 'rb' is ignored, the returned file object does not work with raw bytes.

Yes, the problem is in FileType.__call__ - the handling of '-' is pretty simplistic. Patches welcome.

Roger that. I'll start on a patch for this in a month or two if all goes well.

Steven, patch attached. I lost steam in the unittests with all the meta, suffice it that the names match the file descriptors of the stream sources. i.e. FileType('rb') would give a file with name=0, and so forth. My chosen method also allows other mode flags as well as custom bufsizes.

I don't know how if this is the perfect solution but it keeps the program from crashing.

1154c1154,1157
<                 return _sys.stdin
---
>                 if 'b' in self._mode:
>                     return _sys.stdin.buffer
>                 else:
>                     return _sys.stdin
1156c1159,1162
<                 return _sys.stdout
---
>                 if 'b' in self._mode:
>                     return _sys.stdout.buffer
>                 else:
>                     return _sys.stdout

The fix looks right, but we definitely need a test. I tried to write one, but I'm not sure how to do this properly given how test_argparse redirects standard input and output (so that fileno() doesn't work anymore). I've attached my current (failing) attempt to test this.