RFE: improve error message for CLI export onto existing file

[mtbcarroll]

bin/omero export --file /tmp/foo.ome.tif Image:1

produces some nasty error about invalid NewFileType('wb') if /tmp/foo.ome.tif already exists. Perhaps we could improve the message.

[cblackburn]

It looks like this is arising in ​omero_ext/argparse.py where any message in the ValueError is ignored in favour of a generic message created at this point. We could patch our local copy of argparse.py to handle this but do we want to do that now that this package is bundled with the Python standard library?

[jamoore]

I'd say we shouldn't be patching argparse.

[cblackburn]

I'd agree, especially as it is slated from removal from omero_ext. We may be able to tidy up the output bu I am not sure how easy it would be to provide the actual message. For the longer term, maybe raise and issue against argpase?

[cblackburn]

Ah, I think I have it:

ls30778:openmicroscopy colin$ omero export --file foo.ome.tif Image:1
usage: /Users/colin/Work/repos/openmicroscopy/dist/bin/omero export
       [-h] -f FILE [-t {TIFF,XML}] [--iterate] [-C] [-s SERVER] [-p PORT]
       [-g GROUP] [-u USER] [-w PASSWORD] [-k KEY] [--sudo ADMINUSER] [-q]
       obj
/Users/colin/Work/repos/openmicroscopy/dist/bin/omero export: error: argument -f/--file: File exists: foo.ome.tif

[cblackburn]

See ​https://github.com/openmicroscopy/openmicroscopy/pull/4088