Global pip installs can be broken for users other than the installer.

[thanatos]

• Pip version: 8.1.2
• Python version: 3.5.2
• Operating System: OS X

Description:

pip will install a package that is broken for other users.

Say I have two user accounts on my machine, alice and bob; if alice does the following,

$ pip3 install --user six
$ # then, later,
$ pip3 install ipython

The second command installs ipython globally; however, it does not install six, a dependency of ipython, because it believes that dependency to be fulfilled by the user-only install of it. As a result, ipython will work for alice, but not bob.

This is perhaps somewhat subjective, but I expect global pip installs to be global, and not depend on the state of the user who is running pip. If pip here excluded --user installs when determining if a dependency was met, the package would install correctly.

(I find it acceptable for --user packages to shadow global ones; this could result in the situation whereby a user has an incompatible version installed in --user that the global install can not use, but this situation is already possible today, and seems hard to eliminate without some sort of concept of what emerge calls slots.)

What I've run:

$ pip3 install --user six
$ # then, later,
$ pip3 install ipython

[pradyunsg]

Hey @thanatos! Thanks for filing this issue and sorry for the lack of a response all this while.

This is indeed an interesting problem and I'm not sure how exactly this can be addressed. I'm gonna link this to #4575 since this could be something that would benefit from that change.

[pradyunsg]

This is expected to happen, due to how redistributors modify pip/Python. We've since worked on a solution (described in https://peps.python.org/pep-0668/) for this.