Comment 3 for bug 1726004

MTP is awful, I agree. I'd suggest you simply use one fo the wireless conenction methods instead and avoid it all together. https://manual.calibre-ebook.com/faq.html#how-do-i-use-calibre-with-my-android-phone-tablet-or-kindle-fire-hd

To answer your question, calibre is mostly python, but some parts are C, such as the parts that interface witht he OSes MTP implementation.