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12e12d066d
Moving the preview features to top-level concepts and pushing the
pip-compatible interface down.
e.g.
<img width="291" alt="Screenshot 2024-06-27 at 7 03 48 AM"
src="500ad97d-899d-4051-b59d-e74786b3a45f">
130 lines
4.4 KiB
Markdown
130 lines
4.4 KiB
Markdown
**Warning: This documentation refers to experimental features that may change.**
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# Toolchains
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A Python toolchain is composed of a Python interpreter (i.e. the `python` executable), the standard library, and other supporting files. It is common for an operating system to come with a Python toolchain installed and there are many tools to help manage Python toolchains.
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## Requesting a toolchain
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uv will automatically download a toolchain if it cannot be found.
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In stable commands, this behavior requires enabling preview mode. For example, when creating a virtual environment:
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```bash
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uv venv --preview --python 3.11.6
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```
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uv will ensure that Python 3.11.6 is available — downloading and installing it if necessary — then create the virtual environment with it.
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For commands that are in preview, like `uv sync`, preview behavior is always on.
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```bash
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uv sync --python 3.12.3
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```
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Many toolchain request formats are supported:
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- `<version>` e.g. `3`, `3.12`, `3.12.3`
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- `<version-specifier>` e.g. `>=3.12,<3.13`
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- `<implementation>` e.g. `cpython` or `cp`
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- `<implementation>@<version>` e.g. `cpython@3.12`
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- `<implementation><version>` e.g. `cpython3.12` or `cp312`
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- `<implementation><version-specifier>` e.g. `cpython>=3.12,<3.13`
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- `<implementation>-<version>-<os>-<arch>-<libc>` e.g. `cpython-3.12.3-macos-aarch64-none`
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At this time, only CPython downloads are supported. However, PyPy support is planned.
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## Installing a toolchain
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Sometimes it is preferable to install the toolchains before they are needed.
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To install a toolchain at a specific version:
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```bash
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uv toolchain install 3.12.3
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```
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To install the latest patch version:
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```bash
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uv toolchain install 3.12
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```
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To install a version that satisfies constraints:
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```bash
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uv toolchain install '>=3.8,<3.10'
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```
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To install multiple versions:
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```bash
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uv toolchain install 3.9 3.10 3.11
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```
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## Installing project toolchains
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By default `uv toolchain install` will verify that a managed toolchain is installed or install the latest version.
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However, a project may define a `.python-version` file specifying the default Python toolchain to be used. If present,
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uv will install the toolchain listed in the file.
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Alternatively, a project that requires multiple Python versions may also define a `.python-versions` file. If present,
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uv will install all of the toolchains listed in the file. This file takes precedence over the `.python-version` file.
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uv will also respect Python requirements defined in a `pyproject.toml` file during project command invocations.
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## Viewing available toolchains
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To list installed and available toolchains:
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```bash
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uv toolchain list
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```
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By default, downloads for other platforms and old patch versions are hidden.
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To view all versions:
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```bash
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uv toolchain list --all-versions
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```
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To view toolchains for other platforms:
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```bash
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uv toolchain list --all-platforms
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```
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To exclude downloads and only show installed toolchains:
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```bash
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uv toolchain list --only-installed
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```
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## Adjusting toolchain preferences
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By default, uv will attempt to use Python toolchains found on the system and only download managed interpreters when necessary.
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However, It's possible to adjust uv's toolchain selection preference with the `toolchain-preference` option.
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- `only-managed`: Only use managed toolchains, never use system toolchains.
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- `prefer-installed-managed`: Prefer installed managed toolchains, but use system toolchains if not found. If neither can be
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found, download a managed interpreter.
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- `prefer-managed`: Prefer managed toolchains, even if one needs to be downloaded, but use system toolchains if found.
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- `prefer-system`: Prefer system toolchains, only use managed toolchains if no system interpreter is found.
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- `only-system`: Only use system toolchains, never use managed toolchains.
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These options allow disabling uv's managed toolchains entirely or always using them and ignoring any existing system installations.
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## Discovery order
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When searching for a toolchain, the following locations are checked:
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- Managed toolchains in the `UV_TOOLCHAIN_DIR`.
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- A Python interpreter on the `PATH` as `python3` on macOS and Linux, or `python.exe` on Windows.
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- On Windows, the Python interpreter returned by `py --list-paths` that matches the requested
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version.
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If a specific Python version is requested, e.g. `--python 3.7`, additional executable names are included in the search:
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- A Python interpreter on the `PATH` as, e.g., `python3.7` on macOS and Linux.
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