Disable upgrades to existing python modules which were not installed via pip

What’s the problem this feature will solve?

pip lets me upgrade python modules installed by the system package manager

Describe the solution you’d like

pip should not touch packages not installed by it 😉

$ rpm -qf /usr/lib64/python2.7/site-packages/nacl
python2-pynacl-1.2.0-2.fc28.x86_64

$ pip freeze
cffi==1.11.5
ply==3.9
pycparser==2.14
PyNaCl==1.2.0
six==1.11.0

$ sudo pip install --upgrade pynacl
...
Successfully installed pycparser-2.18 pynacl-1.2.1

Alternative Solutions

🤔

Additional context

I initially posted it here. For starters, I have opened a PR to make pip_installed_by_pip() function more generic so that it can be used by whoever implements this feature.

[ncoghlan]

I agree with @dstufft that only touching files installed specifically by pip by default would be problematic, since it inhibits migrating to pip from other non-system installers.

What I do like though is the notion of being able to configure pip to be more opinionated about what it’s willing to touch, and provide a reasonably helpful error message when refusing to modify things. That way a distro-provided pip can ship with that configuration set, and python3 -m pip --upgrade pip will fail with guidance on what the user should do instead.

I’m thinking along the lines of a python-installers.toml file that can appear alongside any pip.conf with entries like:

[installer.dnf]
modify = false
message = "This is a system managed package, use `dnf` to update it."

(Tangentially related: https://github.com/pypa/pip/pull/5424 is a proposal to provide a way to add an extra “wrapper” identifier to the User Agent info that pip sends to PyPI. If that ends up being pursued, then it may make sense to structure it so that the wrapper info also ends up in the INSTALLER file)

[pradyunsg]

This is now covered by https://peps.python.org/pep-0668/.