I don't think this is correct. In the Calibre repository on Github, there is a p...

I don't think this is correct. In the Calibre repository on Github, there is a page on the progress being made porting to Python 3[0], and a pull request that tracked the progress and has been merged into master[1].

[0] https://github.com/kovidgoyal/calibre/blob/master/README.pyt...

[1] https://github.com/kovidgoyal/calibre/pull/870