Behavior of --user in virtualenv

[sjml]

• Pip version: 9.0.1
• Python version: 2.7.10
• Operating System: macOS 10.12.1

Description:

I've set up a user-specific pip.conf file to make all installations apply the --user flag, like so:

%> cat ~/.pip/pip.conf
[install]
user = true

This is especially handy in a multi-user system, so individuals can avoid accidentally polluting the global Python installation, but it has a lot of value on a single-user system as well, since it reduces the use of sudo.

When using a standard virtual environment, though, we get the expected error:

(venv) %> pip install flask
Can not perform a '--user' install. User site-packages are not visible in this virtualenv.

It's good to have a warning explaining why this fails, but is there a reason it's not simply ignored altogether? Since the documentation acknowledges that the --user flag has no application in a virtual environment, why not treat it as a no-op? I assume the pip team is smarter than I am, so I'm genuinely curious as to whether its a matter of simpler operation, less surprise, etc.

I know I could make a virtualenv-specific configuration file, but there's no simple way to have it automatically apply to each new virtual environment. #2081 goes over some of this same territory, but it doesn't look like it was ever addressed.

Any insight or persistent solutions would be appreciated; I'm sure this can't be a unique situation.

(Thanks pip team for your great work! Anyone who remembers Python development before pip knows how valuable this project is; the fact that it's taken me this long to run into any issues is a testament to the quality here. 👏 👍 )

[sjml]

I'm assuming this doesn't merit a response from the team, but if anyone else is interested, I made a very simple shell function that wraps pip, serving as a guard to keep everything user-installed unless you're in a virtual environment.

[piotr-dobrogost]

I'm assuming this doesn't merit a response from the team

I'm pretty sure it does and I agree that --user should be a no-op inside virtualenv. This needs to be solved if pip were to default to --user as described in issue #1668.

[pfmoore]

It sounds reasonable to me that --user should do nothing in a virtualenv (although maybe it should work if the virtualenv has --system-site-packages). I'd be OK with a PR to make this happen.

The reason for slow progress on anything related to --user is that (as far as I know) it's a fairly infrequently used core Python capability, so we don't have a lot of experience with how it works in real life situations. It's a bit of a chicken-and-egg situation, though, so incremental improvements like this in the UX with --user will help.

[piotr-dobrogost]

As to --user working when --system-site-packages was given to virtualenv; it doesn't look like packages installed with --user are visible in such virtualenv – The --system-site-packages Option

[pfmoore]

I'm not sure that comment's completely clear. I'd be inclined to suggest someone tests it. Also, I don't know if Python 3 "venv" style virtual environments work the same.

In any case, I'd be just as happy to argue that --system-site-packages should see user packages as well. That's one of the many design decisions that probably need to be thrashed out in this area.

[pfmoore]

Update: I just tested and both virtualenv and venv environments can see --user when created with --system-site-packages.

(Interestingly, venv --system-site-packages doesn't install pip into the venv. Possibly because it sees pip is already installed, via the system site-packages, and so skips installing it. It's a debatable point whether this is correct behaviour...)

[piotr-dobrogost]

Update: I just tested and both virtualenv and venv environments can see --user when created with --system-site-packages.

I raised Document access to --user installed packages in --system-site-packages virtualenv for this.
As to not installing pip I think it should be raised as an issue if only to document this behavior.