Discourage usage of pip as root

[dereisele]

What's the problem this feature will solve?
On Manjaro Linux and many other distros, pip tries to install packages in the main library directory (/usr/lib/python37/site-packages), which throws a no permission error. New users than run the same command with sudo. This will result in a messed up library directory when the user installs Python based packages with the system package manager (pacman, apt, ...)

Describe the solution you'd like
I would like a warning or confirmation when pip is run as root (outside a venv) like:
"Running pip as root could result in corruption of the packages directory when a package manager is used. Continue? [yN]"
This confirmation should be able to be bypass with a flag for edge cases like in Docker containers.

Alternative Solutions
Another approach would be to enable the --user flag as default outside venvs.

Additional context
A friend of mine tried to install docker-compose via pacman and was unable to install dependencies like python-requests because pip already created these files. This problem is common and fixing it is tideous work that takes ages.

Disclaimer
I'm on my phone so I can not guarantee correct paths and package names.

[chrahunt]

Just a note, #1668 proposes to default to --user.

[winsonluk]

Here's #9394 as an example:

$ sudo pip3 install
WARNING: Running pip as root is not recommended. This could result in the corruption of the package directories when a package manager is used. See #6409 for more details.
ERROR: You must give at least one requirement to install (see "pip help install")

...and as a reference, here's how brew handles sudo brew:

$ sudo brew
Password:
Error: Running Homebrew as root is extremely dangerous and no longer supported.
As Homebrew does not drop privileges on installation you would be giving all
build scripts full access to your system.

[berniekirby]

Very annoying when you are a sysad and have to install things via pip that are 'global' for all users. I know what I'm doing if I install as root.
Not everyone has a standard python install location - eg a cluster which in my case has numerous different python versions that are not the OS supplied python.
Suggest a different tack or remove the WARNING altogether. People need to take the consequences of their actions if they are not competent to work as 'root'. Don't baby sit them.

[pfmoore]

Don't baby sit them.

To be honest, that's easy to say but we get a lot of support issues from people who do use pip as root and end up in a mess that they don't know how to solve. The warning is an attempt to reduce our support workload by giving people advice before they get into trouble. Surely anyone who knows enough to be able to use pip as root safely is also able to ignore a warning?