Bit of PSA. I've a seen a number of tox4 fixup-related patches where people are adding the following to the 'setup.py' file: py_modules=[] If you're thinking about doing this, please stop. If you recently did this, consider proposing a patch to it again [*]. It's not doing what you think it is. This value should only be set for projects that do not actually distribute any Python code as part of their sdist (for example: puppet modules). Assuming you're not in this category, what you're actually seeing is a bug [1] which requires a fix in pbr [2]. This is a fix for pbr that means the pbr machinery will correctly function under tox4. This should be released very soon. Stephen [*] This obviously can't merge until the pbr fix is released. [1] https://github.com/tox-dev/tox/issues/2712 [2] https://review.opendev.org/c/openstack/pbr/+/869082