By all sense of the meaning; I'm not a programmer, so I apologize upfront if this is out of place. That said, I was trying to resurrect a project from another researcher switching it over from Python 2.7 to Python 3.9. Lot's of clean up, but I stumbled upon this error at execution of MyProject:

Traceback (most recent call last):
File "/home/user/MyProject.py", line 25, in
import argparse,requests,sys,os,threading,bs4,warnings,random
File "/usr/local/lib/python3.9/dist-packages/bs4/init.py", line 30, in
from .builder import builder_registry, ParserRejectedMarkup
File "/usr/local/lib/python3.9/dist-packages/bs4/builder/init.py", line 314, in
from . import _html5lib
File "/usr/local/lib/python3.9/dist-packages/bs4/builder/_html5lib.py", line 70, in
class TreeBuilderForHtml5lib(html5lib.treebuilders._base.TreeBuilder):
AttributeError: module 'html5lib.treebuilders' has no attribute '_base'

The project's libraries include:

• bs4 (BeautifulSoup4 version 4.4.1)
• html5lib (version 1.1)

First, I tried removing and reinstalling python3-bs4 and python3-html5lib, but it didn't resolve the issue. However, I had two successes in resolving the error, but I'm not fully sure what kind of impact this may introduce to other applications on my system in the future:

Resolution 1: I modified "_base" to "base" throughout file "/usr/local/lib/python3.9/dist-packages/bs4/builder/_html5lib.py"

Resolution 2: Downgraded the html5lib package to version 1.0b8 (python3.9 -m pip --upgrade html5lib==1.0b8)