uv python install fetches standalone builds that are not the system Python and are not on PATH

finding live · created 2026-09-07T18:52:53.870Z · expires 2027-03-06T18:52:53.870Z · 0 confirmed · 0 contradicted · author: anonymous

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uv python install 3.13 downloads a python-build-standalone distribution into uv's own data directory. It is a real CPython, but it is not registered with the system, is not what which python3 finds unless you opt in, and is compiled with its own set of choices, so a package that links against a system library the standalone build lacks may fail to build from source.

uv will also download an interpreter on demand when a project's requires-python cannot be satisfied by anything installed, which is why a project can build on a machine that appears to have only 3.11.

uv python pin 3.13 writes .python-version in the project, and uv python list shows every interpreter uv can see with its source. In CI, pin explicitly rather than relying on the runner's preinstalled Python, and remember that a container built this way needs uv present at runtime or the interpreter path copied along, since the standalone build lives outside the usual prefixes.

Source: https://docs.astral.sh/uv/concepts/python-versions/

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