Uv Knowledge Patch

uv Knowledge Patch

Use this guidance when changing uv-managed Python projects, environments, dependency resolution, package indexes, publishing, or CI and container workflows. Confirm the installed uv version and the repository's manifests, lockfiles, configuration, and tests before applying compatibility advice.

Working Method

1. Run uv self version to identify uv itself. uv version reads or changes the current project's version and errors outside a project.
2. Inspect pyproject.toml, uv.toml, .python-version, uv.lock, relevant pylock*.toml inputs, requirements files, and container configuration.
3. Identify which commands and settings are preview behavior. Avoid making a durable workflow depend on preview behavior without pinning and testing it.
4. Read the task-specific reference below before choosing flags or settings.
5. Preserve lock intent: use uv lock --check or --locked for verification; reserve uv lock --refresh for deliberate canonical regeneration.
6. Treat credentials, certificate overrides, publishing, archive validation, environment replacement, and interpreter selection as state-sensitive.
7. Prefer observed project behavior and tests when a newer installed uv differs from this guidance.

Reference Index

Breaking Changes and Deprecations

Initialization now creates a packaged project

uv init <name> creates a src/ package, project script, and uv_build configuration, then installs the project. Use --no-package when the former unpackaged main.py layout is intended. The older uv init --project spelling is deprecated; pass the target path positionally.

Pre-release resolution can fall back automatically

The default if-necessary policy tries stable candidates first and then permits pre-releases when no stable candidate satisfies active constraints, including constraints found transitively. Use --prerelease disallow, allow, or explicit when the policy must be unambiguous. The if-necessary-or-explicit name is deprecated.

Lock and requirements validation is stricter

• uv lock --check and --locked reject non-canonically formatted uv.lock; use uv lock --refresh for an intentional rewrite.
• A --require-hashes directive inside a requirements file enables hash mode for uv pip install and uv pip sync. Every requirement must then be pinned and hashed, and MD5 alone is insufficient.
• PEP 751 files require a packages array and a valid pylock.toml or pylock.<name>.toml filename. Declared artifact sizes are checked.
• Nonexistent local extras, missing frozen groups, and unknown group object specifiers are errors. Do not combine --frozen with --no-sources.

Index and trust failures are fail-closed

With the default first-index strategy, a 401 or 403 stops lookup. Set authenticate = "always" when credentials are mandatory, and add ignore-error-codes only for an index whose unusual behavior requires fallthrough. Explicit invalid SSL_CERT_FILE or SSL_CERT_DIR values no longer fall back to default trust roots.

Archive handling rejects ambiguous or dangerous inputs

ZIP archives with duplicate or ambiguous entries are rejected. Source distributions must use .tar.gz or the accepted legacy .zip form, and wheels are rejected when entry points or data files could overwrite a Python interpreter. Keep insecure ZIP validation bypasses temporary and exceptional.

Platform and image defaults moved

• The linux platform alias means manylinux_2_28; request x86_64-manylinux_2_17 explicitly for the older target.
• Floating container images use Debian 13 Trixie and Alpine 3.22. Removed tags include Bookworm, Alpine 3.21, and Python 3.8.
• Derived images default UV_TOOL_BIN_DIR to /usr/local/bin; override it for an unprivileged user that cannot write there.

Environment replacement is guarded

Interactive uv venv prompts before removing an existing environment and refuses to remove a directory that is not a virtual environment. Use --clear for explicit replacement or --no-clear to prohibit it.

High-Value Workflows

Check lockfile and environment freshness

uv lock --check
uv sync --check

A stale lockfile or environment returns status 1; status 2 is an operational error. Keep that distinction in CI. Isolated operations do not update uv.lock.

Target workspace operations precisely

uv workspace list --paths
uv workspace dir
uv check --package my-package
uv check --all-packages

Workspace listing and directory discovery are stable scripting interfaces. Package selection for uv check is preview behavior. Workspace metadata can include best-effort active-environment information, so its output may depend on the invoking environment.

Control dependency resolution

• Use tool.uv.build-constraint-dependencies for build-time constraints, including ephemeral uv run --with, tools, and inline scripts.
• Use default-groups = "all", per-group requires-python, and tool.uv.required-environments to control group inclusion and wheel coverage.
• Prefer exclude-dependencies, selective --no-sources-package, bounds, and package-specific or relative exclude-newer cutoffs over broad global workarounds.
• Marker-aware uv upgrade can update multiple declarations of one package when environment markers distinguish them.

Exchange standardized results

uv export -o pylock.toml
uv pip compile -o pylock.toml requirements.in
uv pip sync pylock.toml
uv pip install -r pylock.toml

uv can generate, export, install, and sync PEP 751 lockfiles. CycloneDX export produces an SBOM and includes artifact URLs and hashes. Preview sync output can report package changes as JSON.

Select Python deliberately

• uv python install honors UV_PYTHON before .python-version.
• In uv pip compile, -p means --python, not --python-version.
• Unversioned installation and automatic-download defaults favor Python 3.14. Discovery may select a free-threaded 3.14+ interpreter without a t suffix, while installation still prefers a GIL-enabled build.
• Global Python pins can affect new tool environments, but an existing tool retains its interpreter until reinstalled or explicitly changed.

Run tools and ephemeral requirements safely

uvx <name> verifies that the named package or one of its dependencies provides the executable. Use uvx --from <package> <command> when package and command intentionally differ. uv run --with executes in a fresh empty layer over a cached requirement environment, so runtime inspection or mutation does not target the cached layer itself.

Audit, format, and publish with explicit stability choices

• uv audit, uv format, uv sync JSON output, relocatable environments, package-level workspace conflicts, and several check, index, publishing, and malware-screening features are preview behavior.
• Pin Ruff with uv format --version when formatting reproducibility matters; the formatter's default style can change.
• Publishing supports stored uv auth credentials, PEP 740 attestations, Trusted Publishing with pyx, S3 pre-signed URLs, and GCS signing. Verify the stability and trust path selected by the workflow.

Final Checks

• Confirm stable versus preview status for every command added to automation.
• Re-run lock and environment checks after dependency or project-version changes.
• Test the intended Python implementation, GIL mode, and target platform for cross-platform artifacts.
• Verify index names, authentication policy, credential username, proxy, timeout, and certificate settings before diagnosing resolution failures.
• Pin formatter behavior and container tags when reproducibility matters.
• Inspect archive and lockfile inputs before weakening validation.