Respect UV_PYTHON_PREFERENCE environment variable (#159)

Signed-off-by: Bernát Gábor <bgabor8@bloomberg.net>

Author: gaborbernat

.github/workflows/check.yaml

@@ -37,14 +37,17 @@ jobs:
           enable-cache: true
           cache-dependency-glob: "pyproject.toml"
       - name: Install tox
-        run: uv tool install --python-preference only-managed --python 3.13 tox --with tox-uv
+        run: uv tool install --python-preference only-managed --python 3.13 tox --with .
       - name: Install Python
         if: startsWith(matrix.env, '3.') && matrix.env != '3.13'
         run: uv python install --python-preference only-managed ${{ matrix.env }}
       - name: Setup test suite
         run: tox run -vv --notest --skip-missing-interpreters false -e ${{ matrix.env }}
+        env:
+          UV_PYTHON_PREFERENCE: "only-managed"
       - name: Run test suite
         run: tox run --skip-pkg-install -e ${{ matrix.env }}
         env:
           PYTEST_ADDOPTS: "-vv --durations=20"
           DIFF_AGAINST: HEAD
+          UV_PYTHON_PREFERENCE: "only-managed"

.pre-commit-config.yaml

@@ -13,7 +13,7 @@ repos:
     rev: v2.3.0
     hooks:
       - id: codespell
-        additional_dependencies: ["tomli>=2.0.2"]
+        additional_dependencies: ["tomli>=2.2.1"]
   - repo: https://github.com/tox-dev/tox-ini-fmt
     rev: "1.4.1"
     hooks:

pyproject.toml

@@ -2,7 +2,7 @@
 build-backend = "hatchling.build"
 requires = [
   "hatch-vcs>=0.4",
-  "hatchling>=1.25",
+  "hatchling>=1.27",
 ]
 
 [project]
@@ -40,10 +40,10 @@ dynamic = [
   "version",
 ]
 dependencies = [
-  "packaging>=24.1",
-  "tox>=4.21.2,<5",
+  "packaging>=24.2",
+  "tox>=4.24.1,<5",
   "typing-extensions>=4.12.2; python_version<'3.10'",
-  "uv>=0.4.18,<1",
+  "uv>=0.5.21,<1",
 ]
 urls.Changelog = "https://github.com/tox-dev/tox-uv/releases"
 urls.Documentation = "https://github.com/tox-dev/tox-uv#tox-uv"
@@ -62,14 +62,14 @@ dev = [
 test = [
   "covdefaults>=2.3",
   "devpi-process>=1.0.2",
-  "diff-cover>=9.2",
-  "pytest>=8.3.3",
-  "pytest-cov>=5",
+  "diff-cover>=9.2.1",
+  "pytest>=8.3.4",
+  "pytest-cov>=6",
   "pytest-mock>=3.14",
 ]
-type = [ "mypy==1.11.2", { include-group = "test" } ]
-lint = [ "pre-commit-uv>=4.1.3" ]
-pkg-meta = [ "check-wheel-contents>=0.6", "twine>=5.1.1", "uv>=0.4.18" ]
+type = [ "mypy==1.14.1", { include-group = "test" } ]
+lint = [ "pre-commit-uv>=4.1.4" ]
+pkg-meta = [ "check-wheel-contents>=0.6.1", "twine>=6.1", "uv>=0.5.21" ]
 
 [tool.hatch]
 build.hooks.vcs.version-file = "src/tox_uv/version.py"

src/tox_uv/_venv.py

@@ -73,7 +73,7 @@ def register_config(self) -> None:
         self.conf.add_config(
             keys=["uv_python_preference"],
             of_type=cast("Type[Optional[PythonPreference]]", Optional[PythonPreference]),  # noqa: UP006
-            default="system",
+            default=lambda conf, name: self.environment_variables.get("UV_PYTHON_PREFERENCE", "system"),  # noqa: ARG005
             desc=(
                 "Whether to prefer using Python installations that are already"
                 " present on the system, or those that are downloaded and"

tests/conftest.py

@@ -33,6 +33,11 @@ def demo_pkg_inline(root: Path) -> Path:
     return root / "demo_pkg_inline"
 
 
+@pytest.fixture
+def clear_python_preference_env_var(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.delenv("UV_PYTHON_PREFERENCE", raising=False)
+
+
 pytest_plugins = [
     "tox.pytest",
 ]

tests/test_tox_uv_lock.py

@@ -10,6 +10,7 @@
     from tox.pytest import ToxProjectCreator
 
 
+@pytest.mark.usefixtures("clear_python_preference_env_var")
 def test_uv_lock_list_dependencies_command(tox_project: ToxProjectCreator) -> None:
     project = tox_project({
         "tox.ini": """
@@ -70,6 +71,7 @@ def test_uv_lock_list_dependencies_command(tox_project: ToxProjectCreator) -> No
         assert calls[i] == expected[i]
 
 
+@pytest.mark.usefixtures("clear_python_preference_env_var")
 @pytest.mark.parametrize("verbose", ["", "-v", "-vv", "-vvv"])
 def test_uv_lock_command(tox_project: ToxProjectCreator, verbose: str) -> None:
     project = tox_project({
@@ -131,6 +133,7 @@ def test_uv_lock_command(tox_project: ToxProjectCreator, verbose: str) -> None:
     assert show_uv_output is (bool(verbose))
 
 
+@pytest.mark.usefixtures("clear_python_preference_env_var")
 def test_uv_lock_with_dev(tox_project: ToxProjectCreator) -> None:
     project = tox_project({
         "tox.ini": """
@@ -166,6 +169,7 @@ def test_uv_lock_with_dev(tox_project: ToxProjectCreator) -> None:
     assert calls == expected
 
 
+@pytest.mark.usefixtures("clear_python_preference_env_var")
 @pytest.mark.parametrize(
     "name",
     [
@@ -229,6 +233,7 @@ def test_uv_lock_with_install_pkg(tox_project: ToxProjectCreator, name: str) ->
     assert calls == expected
 
 
+@pytest.mark.usefixtures("clear_python_preference_env_var")
 def test_uv_sync_extra_flags(tox_project: ToxProjectCreator) -> None:
     project = tox_project({
         "tox.ini": """
@@ -281,6 +286,7 @@ def test_uv_sync_extra_flags(tox_project: ToxProjectCreator) -> None:
     assert calls == expected
 
 
+@pytest.mark.usefixtures("clear_python_preference_env_var")
 def test_uv_sync_extra_flags_toml(tox_project: ToxProjectCreator) -> None:
     project = tox_project({
         "tox.toml": """
@@ -333,6 +339,7 @@ def test_uv_sync_extra_flags_toml(tox_project: ToxProjectCreator) -> None:
     assert calls == expected
 
 
+@pytest.mark.usefixtures("clear_python_preference_env_var")
 def test_uv_sync_dependency_groups(tox_project: ToxProjectCreator) -> None:
     project = tox_project({
         "tox.toml": """

tests/test_tox_uv_venv.py

@@ -41,6 +41,36 @@ def test_uv_venv_pass_env(tox_project: ToxProjectCreator) -> None:
     assert "PKG_CONFIG_PATH" in pass_through
 
 
+@pytest.mark.usefixtures("clear_python_preference_env_var")
+def test_uv_venv_preference_system_by_default(tox_project: ToxProjectCreator) -> None:
+    project = tox_project({"tox.ini": "[testenv]"})
+
+    result = project.run("c", "-k", "uv_python_preference")
+    result.assert_success()
+
+    parser = ConfigParser()
+    parser.read_string(result.out)
+    got = parser["testenv:py"]["uv_python_preference"]
+
+    assert got == "system"
+
+
+def test_uv_venv_preference_override_via_env_var(
+    tox_project: ToxProjectCreator, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    project = tox_project({"tox.ini": "[testenv]"})
+    monkeypatch.setenv("UV_PYTHON_PREFERENCE", "only-managed")
+
+    result = project.run("c", "-k", "uv_python_preference")
+    result.assert_success()
+
+    parser = ConfigParser()
+    parser.read_string(result.out)
+    got = parser["testenv:py"]["uv_python_preference"]
+
+    assert got == "only-managed"
+
+
 def test_uv_venv_spec(tox_project: ToxProjectCreator) -> None:
     ver = sys.version_info
     project = tox_project({"tox.ini": f"[testenv]\npackage=skip\nbase_python={ver.major}.{ver.minor}"})

tox.ini

@@ -1,7 +1,7 @@
 [tox]
 requires =
-    tox>=4.2
-    tox-uv>=1.11.3
+    tox>=4.24.1
+    tox-uv>=1.19.1
 env_list =
     fix
     3.13
@@ -36,7 +36,7 @@ dependency_groups = test
 description = format the code base to adhere to our styles, and complain about what we cannot do automatically
 skip_install = true
 deps =
-    pre-commit-uv>=4.1.3
+    pre-commit-uv>=4.1.4
 commands =
     pre-commit run --all-files --show-diff-on-failure