pip --user by default

[Skip Montanaro]

>> Inside of a virtualenv, what's the difference between a --user install
>> and a system one?
>>
>
> It errors out:
>
> % pip install --user urllib3
> Can not perform a '--user' install. User site-packages are not visible
> in this virtualenv.

I was able to 'pip install --user ...' a package yesterday in a Conda
environment, so I think it's a YMMV sort of thing. Having only ever
used the Conda environment stuff, I've generally interpreted the term
"virtual environment" in a fairly generic way.

Skip