[Quoth]

Something amiss with python?
Also why is path not reported?
Have you really no plug-ins installed?

Your install
calibre-debug -g
calibre 6.13 embedded-python: False

Interface language: fr
QPA platform: xcb
devicePixelRatio: 1.0

My install
calibre-debug -g
calibre 7.16 embedded-python: True

Interface language: None
EXE path: /opt/calibre/bin/calibre-debug
Successfully initialized third party plugins: DeACSM (0, 0, 16) && DeDRM (10, 0, 3) && Amazon.com Multiple Countries (1, 0, 0) && Annotations (1, 17, 13) && Author Book Count (2, 2, 3) && Barnes & Noble (1, 5, 6) && Comments Cleaner (1, 14, 0) && Copy Cover To Device (2, 0, 4) && Diaps Editing Toolbag (0, 4, 0) && EpubCheck (0, 2, 5) && EpubMerge (3, 1, 0) && EpubSplit (3, 8, 0) && Find Duplicates (1, 10, 9) && Generate Cover (2, 3, 4) && Goodreads (1, 8, 2) && Hyphenate This! (0, 1, 3) && KePub Input (3, 6, 6) && KePub Metadata Reader (3, 4, 3) && KePub Metadata Writer (3, 4, 3) && KePub Output (3, 6, 9) && KindleUnpack - The Plugin (0, 83, 1) && Kobo Books (1, 9, 2) && Kobo Utilities (2, 17, 1) && KoboTouchExtended (3, 6, 9) && Library Splitter (1, 0, 7) && Manage Series (1, 5, 2) && Modify ePub (1, 8, 4) && Obok DeDRM (10, 0, 3) && Open With (1, 8, 3) && Quality Check (1, 13, 14) && Quick Preferences (1, 7, 1) && Reading List (1, 15, 4) && Resize Cover (1, 2, 1) && ScrambleEbook (0, 6, 0) && Skoob Books (1, 5, 5) && Smashwords Metadata (1, 0, 2)
QPA platform: xcb
devicePixelRatio: 1.0