After upgrading to Python 3.9, I get this error message when running demo.py:

Traceback (most recent call last):
  File "/home/ngaba/roundup-2.0.0/./demo.py", line 5, in <module>
    from roundup.demo import main
  File "/home/ngaba/roundup-2.0.0/roundup/demo.py", line 20, in <module>
    from roundup.scripts import roundup_server
  File "/home/ngaba/roundup-2.0.0/roundup/scripts/roundup_server.py", line 77, in <module>
    favico = zlib.decompress(base64.decodestring(b'''
AttributeError: module 'base64' has no attribute 'decodestring'


This seems to be a known issue in Python 3.9. (Changing decodestring to decodebytes seems to work, but then Python2 gives an error...)

What is the intended fix here? I am new to Python.