I also ran into this bug after updating my machines during the weekend,
both machines run on Debian Sid.
The issue appeared with some "pip3 install XXX", but is also present on
simple "pip3 list"
I thought it was an issue with Debian shifting to Python 3.8, so I tried
to reinstall a whole bunch of packages of Python 3.7, following the
dependencies. This didn't change anything. After that, I decided to take
the plunge and actually look at the stack trace. python-wheels wasn't to
interesting, but then, I thought it looked like an issue of listing the
version of the package, so it might not be an issue of python or pip,
but an issue of a package. So I tried to print the package name it was
in /usr/lib/python3/dist-packages/pip/_internal/commands/list.py, at
line275 (just before the 'row = [proj.project_name, proj.version]'
line), printed a whole list of packages.
The last name was testpath. I uninstalled python3-testpath (and
incidentaly a whole bunch of packages depending on it), and now, I can
'pip3 list' and 'pip3 install' again.
Now, I have to get my environment to work again after uninstalling all
So I don't know how pip works internally and this work is some blind
guessing to get my system to work again, but maybe it can give a clue to
the maintainer to help debug this, and probably forward the issue to the