I haven't done any programming in a while and I'm not at all familiar with Python but I might give this a try after I finish my little PHP project.
Checked out the source code. Is
'/src/calibre/gui2/add.py' the only affected module? At least just for making the warning more verbose? I don't think I can tackle adding a button for txt/csv export. I haven't even set-up a Calibre/Python development environment.

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