feat: free-threaded python support (#203)

Author: khneal

pyproject.toml

@@ -41,7 +41,7 @@ dynamic = [
 ]
 dependencies = [
   "packaging>=24.2",
-  "tox>=4.24.1,<5",
+  "tox>=4.26,<5",
   "typing-extensions>=4.12.2; python_version<'3.10'",
   "uv>=0.5.31,<1",
 ]

src/tox_uv/_venv.py

@@ -6,6 +6,7 @@
 import logging
 import os
 import sys
+import sysconfig
 from abc import ABC
 from functools import cached_property
 from importlib.resources import as_file, files
@@ -131,6 +132,7 @@ def _get_python(self, base_python: list[str]) -> PythonInfo | None:  # noqa: PLR
                     is_64=sys.maxsize > 2**32,
                     platform=sys.platform,
                     extra={},
+                    free_threaded=sysconfig.get_config_var("Py_GIL_DISABLED") == 1,
                 )
             base_path = Path(base)
             if base_path.is_absolute():
@@ -142,6 +144,7 @@ def _get_python(self, base_python: list[str]) -> PythonInfo | None:  # noqa: PLR
                     is_64=info.architecture == 64,  # noqa: PLR2004
                     platform=info.platform,
                     extra={"executable": base},
+                    free_threaded=info.free_threaded,
                 )
             spec = PythonSpec.from_string_spec(base)
             return PythonInfo(
@@ -157,6 +160,7 @@ def _get_python(self, base_python: list[str]) -> PythonInfo | None:  # noqa: PLR
                 is_64=spec.architecture == 64,  # noqa: PLR2004
                 platform=sys.platform,
                 extra={"architecture": spec.architecture},
+                free_threaded=spec.free_threaded,
             )
 
         return None  # pragma: no cover
@@ -256,25 +260,28 @@ def env_version_spec(self) -> str:
         imp = self.base_python.impl_lower
         executable = self.base_python.extra.get("executable")
         architecture = self.base_python.extra.get("architecture")
+        free_threaded = self.base_python.free_threaded
         if executable:
             version_spec = str(executable)
         elif (
             architecture is None
             and (base.major, base.minor) == sys.version_info[:2]
             and (sys.implementation.name.lower() == imp)
+            and ((sysconfig.get_config_var("Py_GIL_DISABLED") == 1) == free_threaded)
         ):
             version_spec = sys.executable
         else:
             uv_imp = imp or ""
+            free_threaded_tag = "+freethreaded" if free_threaded else ""
             if not base.major:
                 version_spec = f"{uv_imp}"
             elif not base.minor:
-                version_spec = f"{uv_imp}{base.major}"
+                version_spec = f"{uv_imp}{base.major}{free_threaded_tag}"
             elif architecture is not None and self.base_python.platform == "win32":
                 uv_arch = {32: "x86", 64: "x86_64"}[architecture]
-                version_spec = f"{uv_imp}-{base.major}.{base.minor}-windows-{uv_arch}-none"
+                version_spec = f"{uv_imp}-{base.major}.{base.minor}{free_threaded_tag}-windows-{uv_arch}-none"
             else:
-                version_spec = f"{uv_imp}{base.major}.{base.minor}"
+                version_spec = f"{uv_imp}{base.major}.{base.minor}{free_threaded_tag}"
         return version_spec
 
     @cached_property

tests/test_tox_uv_venv.py

@@ -447,6 +447,14 @@ def test_get_python_architecture(base_python: str, architecture: int | None) ->
     assert python_info.extra["architecture"] == architecture
 
 
+@pytest.mark.parametrize(("base_python", "is_free_threaded"), [("py313", False), ("py313t", True)])
+def test_get_python_free_threaded(base_python: str, is_free_threaded: int | None) -> None:
+    uv_venv = _TestUvVenv(create_args=mock.Mock())
+    python_info = uv_venv.get_python_info(base_python)
+    assert python_info is not None
+    assert python_info.free_threaded == is_free_threaded
+
+
 def test_env_version_spec_no_architecture() -> None:
     uv_venv = _TestUvVenv(create_args=mock.MagicMock())
     python_info = PythonInfo(
@@ -510,3 +518,25 @@ def test_env_version_spec_architecture_configured_overwrite_sys_exe() -> None:
     )
     uv_venv.set_base_python(python_info)
     assert uv_venv.env_version_spec() == f"cpython-{major}.{minor}-windows-x86-none"
+
+
+def test_env_version_spec_free_threaded() -> None:
+    uv_venv = _TestUvVenv(create_args=mock.MagicMock())
+    python_info = PythonInfo(
+        implementation="cpython",
+        version_info=VersionInfo(
+            major=3,
+            minor=13,
+            micro=3,
+            releaselevel="",
+            serial=0,
+        ),
+        version="",
+        is_64=True,
+        platform="win32",
+        extra={"architecture": None},
+        free_threaded=True,
+    )
+    uv_venv.set_base_python(python_info)
+    with mock.patch("sys.version_info", (0, 0, 0)):  # prevent picking sys.executable
+        assert uv_venv.env_version_spec() == "cpython3.13+freethreaded"