Calibre 4.5 not starting

[_calm_bomb_]

Just did an update on my system (Fedora 31) and Calibre is not starting anymore, whatever I do. I removed the old config, I moved the library and started from scratch and I still get this issue:

$ calibre
Icon theme "gnome" not found.
Traceback (most recent call last):
  File "/usr/bin/calibre", line 20, in <module>
    sys.exit(calibre())
  File "/usr/lib64/calibre/calibre/gui_launch.py", line 72, in calibre
    main(args)
  File "/usr/lib64/calibre/calibre/gui2/main.py", line 557, in main
    gui_debug=gui_debug)
  File "/usr/lib64/calibre/calibre/gui2/main.py", line 383, in run_gui
    from calibre.gui2.ui import Main
  File "/usr/lib64/calibre/calibre/gui2/ui.py", line 41, in <module>
    from calibre.gui2.init import LibraryViewMixin, LayoutMixin
  File "/usr/lib64/calibre/calibre/gui2/init.py", line 19, in <module>
    from calibre.gui2.book_details import BookDetails
  File "/usr/lib64/calibre/calibre/gui2/book_details.py", line 18, in <module>
    from calibre.ebooks.metadata.book.render import mi_to_html
  File "/usr/lib64/calibre/calibre/ebooks/metadata/book/render.py", line 15, in <module>
    from calibre.library.comments import comments_to_html, markdown
  File "/usr/lib64/calibre/calibre/library/comments.py", line 10, in <module>
    from calibre.ebooks.BeautifulSoup import (
  File "/usr/lib64/calibre/calibre/ebooks/BeautifulSoup.py", line 6, in <module>
    import bs4
  File "/usr/local/lib/python3.7/site-packages/bs4/__init__.py", line 29, in <module>
    from .builder import builder_registry
  File "/usr/local/lib/python3.7/site-packages/bs4/builder/__init__.py", line 303, in <module>
    from . import _htmlparser
  File "/usr/local/lib/python3.7/site-packages/bs4/builder/_htmlparser.py", line 7, in <module>
    from html.parser import (
ImportError: cannot import name 'HTMLParseError' from 'html.parser' (/usr/lib64/python3.7/html/parser.py)

[eschwartz]

This is not a development question, but the answer is that the file

/usr/local/lib/python3.7/site-packages/bs4/builder/_htmlparser.py

is totally broken. And it doesn't belong to calibre, and it doesn't belong to the Fedora package repositories because it is in /usr/local

Have you been sudo pip installing things? Maybe don't do that.