Currently (even in latest uv 0.1.12 that supports --python flag) it's not possible to use uv in case --user flag of pip (or PIP_USER="true" env variable is set).

With --user flag, packages are installed to a ~/.local folder, which means that the user might not have access to the python system installation as a whole, but can locally install and uninstall packages, without having venv.

This is extremely useful for cases like CI and building container images, where having a venv is an extra overhead and it is unnecessary burden.

There is an interesting (and used in Apache Airflow) case for the --user flag (this currently prevent us from using uv by us and our users also in PROD images in addition to our CI image). That is currently a blocker for apache/airflow#37785

Why --user flag is useful and why we use it in Airflow?

Using --user flag is pretty useful when you want to have an optimized image - because such .local folders can be copied between different stage of the image (based on the same base image and prod libraries installed) and you can copy the whole .local folder between the stages after packages are installed - which means that the final stage of the image does not have to have build-essentials/ compilers installed.

You could do the same with venv if you keep it in the same folder, but that looses an essential capability of creating venv dynamically containing all the packages you have in your .local folder. When you have your --user installed packages, and you create a new venv with --system-site-packages, the packages installed in .local folder are also installed in the new venv. This does not work when you create a new venv from another venv because --system-site-packages are only the ones installed in the system.

While I can think of some creative ways (maybe I will find some) - having an equivalent of --user installation by uv pip install would be a great simplification for our case to support the users who want to use uv (and seems that there is already a need for that looking at the apache/airflow#37785