Add free-threaded Python support

.github/workflows/check.yaml

@@ -22,6 +22,7 @@ jobs:
       fail-fast: false
       matrix:
         py:
+          - "3.13t"
           - "3.13"
           - "3.12"
           - "3.11"
@@ -77,27 +78,41 @@ jobs:
         shell: bash
         run: echo ~/.local/bin >> $GITHUB_PATH
       - name: Install tox
-        if: matrix.py == '3.13'
+        if: matrix.py == '3.13' || matrix.py == '3.13t'
         run: uv tool install --python-preference only-managed --python 3.12 tox --with tox-uv
       - name: Install tox
-        if: matrix.py != '3.13'
+        if: "!(matrix.py == '3.13' || matrix.py == '3.13t')"
         run: uv tool install --python-preference only-managed --python 3.13 tox --with tox-uv
       - name: Setup brew python for test ${{ matrix.py }}
-        if: startsWith(matrix.py,'brew@')
+        if: startsWith(matrix.py, 'brew@')
         run: |
           set -e
           PY=$(echo '${{ matrix.py }}' | cut -c 6-)
           brew cleanup && brew upgrade python@$PY || brew install python@$PY
           echo "/usr/local/opt/python@$PY/libexec/bin" >>"${GITHUB_PATH}"
         shell: bash
       - name: Setup python for test ${{ matrix.py }}
-        if: "!( startsWith(matrix.py,'brew@') || endsWith(matrix.py, '-dev') )"
+        if: "!(startsWith(matrix.py, 'brew@') || endsWith(matrix.py, 't'))"
         uses: actions/setup-python@v5
         with:
           python-version: ${{ matrix.py }}
           allow-prereleases: true
+      # quansight-labs to install free-threaded python until actions/setup-python supports it
+      # https://github.com/actions/setup-python/issues/771
+      - name: Setup python for test ${{ matrix.py }}
+        if: endsWith(matrix.py, 't')
+        uses: quansight-labs/[email protected]
+        with:
+          python-version: ${{ matrix.py }}
       - name: Pick environment to run
+        if: matrix.py != '3.13t'
         run: python tasks/pick_tox_env.py ${{ matrix.py }}
+      - name: Pick environment to run
+        if: matrix.py == '3.13t' && runner.os != 'Windows'
+        run: python tasks/pick_tox_env.py ${{ matrix.py }} $Python_ROOT_DIR/bin/python
+      - name: Pick environment to run
+        if: matrix.py == '3.13t' && runner.os == 'Windows'
+        run: python tasks/pick_tox_env.py ${{ matrix.py }} $env:Python_ROOT_DIR\python.exe
       - name: Setup test suite
         run: tox run -vv --notest --skip-missing-interpreters false
       - name: Run test suite

docs/changelog/2809.feature.rst

@@ -0,0 +1 @@
+Add support for selecting free-threaded Python interpreters, e.g., `python3.13t`.

docs/installation.rst

@@ -84,7 +84,7 @@ Python and OS Compatibility
 
 virtualenv works with the following Python interpreter implementations:
 
-- `CPython <https://www.python.org/>`_: ``3.12 >= python_version >= 3.7``
+- `CPython <https://www.python.org/>`_: ``3.13 >= python_version >= 3.7``
 - `PyPy <https://pypy.org/>`_: ``3.10 >= python_version >= 3.7``
 
 This means virtualenv works on the latest patch version of each of these minor versions. Previous patch versions are

docs/user_guide.rst

@@ -86,13 +86,14 @@ format is either:
 
     - the python implementation is all alphabetic characters (``python`` means any implementation, and if is missing it
       defaults to ``python``),
-    - the version is a dot separated version number,
+    - the version is a dot separated version number optionally followed by ``t`` for free-threading,
     - the architecture is either ``-64`` or ``-32`` (missing means ``any``).
 
     For example:
 
     - ``python3.8.1`` means any python implementation having the version ``3.8.1``,
     - ``3`` means any python implementation having the major version ``3``,
+    - ``3.13t`` means any python implementation having the version ``3.13`` with free threading,
     - ``cpython3`` means a ``CPython`` implementation having the version ``3``,
     - ``pypy2`` means a python interpreter with the ``PyPy`` implementation and major version ``2``.
 

src/virtualenv/discovery/cached_py_info.py

@@ -24,6 +24,7 @@
 _CACHE = OrderedDict()
 _CACHE[Path(sys.executable)] = PythonInfo()
 LOGGER = logging.getLogger(__name__)
+_CACHE_FILE_VERSION = 1
 
 
 def from_exe(cls, app_data, exe, env=None, raise_on_error=True, ignore_cache=False):  # noqa: FBT002, PLR0913
@@ -64,8 +65,13 @@ def _get_via_file_cache(cls, app_data, path, exe, env):
     with py_info_store.locked():
         if py_info_store.exists():  # if exists and matches load
             data = py_info_store.read()
-            of_path, of_st_mtime, of_content = data["path"], data["st_mtime"], data["content"]
-            if of_path == path_text and of_st_mtime == path_modified:
+            of_path, of_st_mtime, of_content, version = (
+                data["path"],
+                data["st_mtime"],
+                data["content"],
+                data.get("version"),
+            )
+            if of_path == path_text and of_st_mtime == path_modified and version == _CACHE_FILE_VERSION:
                 py_info = cls._from_dict(of_content.copy())
                 sys_exe = py_info.system_executable
                 if sys_exe is not None and not os.path.exists(sys_exe):
@@ -76,7 +82,12 @@ def _get_via_file_cache(cls, app_data, path, exe, env):
         if py_info is None:  # if not loaded run and save
             failure, py_info = _run_subprocess(cls, exe, app_data, env)
             if failure is None:
-                data = {"st_mtime": path_modified, "path": path_text, "content": py_info._to_dict()}  # noqa: SLF001
+                data = {
+                    "st_mtime": path_modified,
+                    "path": path_text,
+                    "content": py_info._to_dict(),  # noqa: SLF001
+                    "version": _CACHE_FILE_VERSION,
+                }
                 py_info_store.write(data)
             else:
                 py_info = failure

src/virtualenv/discovery/py_info.py

@@ -52,6 +52,7 @@ def abs_path(v):
 
         self.version = sys.version
         self.os = os.name
+        self.free_threaded = sysconfig.get_config_var("Py_GIL_DISABLED") == 1
 
         # information about the prefix - determines python home
         self.prefix = abs_path(getattr(sys, "prefix", None))  # prefix we think
@@ -290,7 +291,12 @@ def __str__(self) -> str:
 
     @property
     def spec(self):
-        return "{}{}-{}".format(self.implementation, ".".join(str(i) for i in self.version_info), self.architecture)
+        return "{}{}{}-{}".format(
+            self.implementation,
+            ".".join(str(i) for i in self.version_info),
+            "t" if self.free_threaded else "",
+            self.architecture,
+        )
 
     @classmethod
     def clear_cache(cls, app_data):
@@ -300,7 +306,7 @@ def clear_cache(cls, app_data):
         clear(app_data)
         cls._cache_exe_discovery.clear()
 
-    def satisfies(self, spec, impl_must_match):  # noqa: C901
+    def satisfies(self, spec, impl_must_match):  # noqa: C901, PLR0911
         """Check if a given specification can be satisfied by the this python interpreter instance."""
         if spec.path:
             if self.executable == os.path.abspath(spec.path):
@@ -326,6 +332,9 @@ def satisfies(self, spec, impl_must_match):  # noqa: C901
         if spec.architecture is not None and spec.architecture != self.architecture:
             return False
 
+        if spec.free_threaded is not None and spec.free_threaded != self.free_threaded:
+            return False
+
         for our, req in zip(self.version_info[0:3], (spec.major, spec.minor, spec.micro)):
             if req is not None and our is not None and our != req:
                 return False
@@ -522,10 +531,14 @@ def _find_possible_exe_names(self):
         for name in self._possible_base():
             for at in (3, 2, 1, 0):
                 version = ".".join(str(i) for i in self.version_info[:at])
-                for arch in [f"-{self.architecture}", ""]:
-                    for ext in EXTENSIONS:
-                        candidate = f"{name}{version}{arch}{ext}"
-                        name_candidate[candidate] = None
+                mods = [""]
+                if self.free_threaded:
+                    mods.append("t")
+                for mod in mods:
+                    for arch in [f"-{self.architecture}", ""]:
+                        for ext in EXTENSIONS:
+                            candidate = f"{name}{version}{mod}{arch}{ext}"
+                            name_candidate[candidate] = None
         return list(name_candidate.keys())
 
     def _possible_base(self):

src/virtualenv/discovery/py_spec.py

@@ -5,7 +5,7 @@
 import os
 import re
 
-PATTERN = re.compile(r"^(?P<impl>[a-zA-Z]+)?(?P<version>[0-9.]+)?(?:-(?P<arch>32|64))?$")
+PATTERN = re.compile(r"^(?P<impl>[a-zA-Z]+)?(?P<version>[0-9.]+)?(?P<threaded>t)?(?:-(?P<arch>32|64))?$")
 
 
 class PythonSpec:
@@ -20,18 +20,21 @@ def __init__(  # noqa: PLR0913
         micro: int | None,
         architecture: int | None,
         path: str | None,
+        *,
+        free_threaded: bool | None = None,
     ) -> None:
         self.str_spec = str_spec
         self.implementation = implementation
         self.major = major
         self.minor = minor
         self.micro = micro
+        self.free_threaded = free_threaded
         self.architecture = architecture
         self.path = path
 
     @classmethod
     def from_string_spec(cls, string_spec: str):  # noqa: C901, PLR0912
-        impl, major, minor, micro, arch, path = None, None, None, None, None, None
+        impl, major, minor, micro, threaded, arch, path = None, None, None, None, None, None, None
         if os.path.isabs(string_spec):  # noqa: PLR1702
             path = string_spec
         else:
@@ -58,6 +61,7 @@ def _int_or_none(val):
                             major = int(str(version_data)[0])  # first digit major
                             if version_data > 9:  # noqa: PLR2004
                                 minor = int(str(version_data)[1:])
+                        threaded = bool(groups["threaded"])
                     ok = True
                 except ValueError:
                     pass
@@ -70,14 +74,15 @@ def _int_or_none(val):
             if not ok:
                 path = string_spec
 
-        return cls(string_spec, impl, major, minor, micro, arch, path)
+        return cls(string_spec, impl, major, minor, micro, arch, path, free_threaded=threaded)
 
     def generate_re(self, *, windows: bool) -> re.Pattern:
         """Generate a regular expression for matching against a filename."""
         version = r"{}(\.{}(\.{})?)?".format(
             *(r"\d+" if v is None else v for v in (self.major, self.minor, self.micro))
         )
         impl = "python" if self.implementation is None else f"python|{re.escape(self.implementation)}"
+        mod = "t?" if self.free_threaded else ""
         suffix = r"\.exe" if windows else ""
         version_conditional = (
             "?"
@@ -89,7 +94,7 @@ def generate_re(self, *, windows: bool) -> re.Pattern:
         )
         # Try matching `direct` first, so the `direct` group is filled when possible.
         return re.compile(
-            rf"(?P<impl>{impl})(?P<v>{version}){version_conditional}{suffix}$",
+            rf"(?P<impl>{impl})(?P<v>{version}{mod}){version_conditional}{suffix}$",
             flags=re.IGNORECASE,
         )
 
@@ -105,6 +110,8 @@ def satisfies(self, spec):
             return False
         if spec.architecture is not None and spec.architecture != self.architecture:
             return False
+        if spec.free_threaded is not None and spec.free_threaded != self.free_threaded:
+            return False
 
         for our, req in zip((self.major, self.minor, self.micro), (spec.major, spec.minor, spec.micro)):
             if req is not None and our is not None and our != req:
@@ -113,7 +120,7 @@ def satisfies(self, spec):
 
     def __repr__(self) -> str:
         name = type(self).__name__
-        params = "implementation", "major", "minor", "micro", "architecture", "path"
+        params = "implementation", "major", "minor", "micro", "architecture", "path", "free_threaded"
         return f"{name}({', '.join(f'{k}={getattr(self, k)}' for k in params if getattr(self, k) is not None)})"
 
 

src/virtualenv/discovery/windows/__init__.py

@@ -27,14 +27,14 @@ def propose_interpreters(spec, cache_dir, env):
         reverse=True,
     )
 
-    for name, major, minor, arch, exe, _ in existing:
+    for name, major, minor, arch, threaded, exe, _ in existing:
         # Map well-known/most common organizations to a Python implementation, use the org name as a fallback for
         # backwards compatibility.
         implementation = _IMPLEMENTATION_BY_ORG.get(name, name)
 
         # Pre-filtering based on Windows Registry metadata, for CPython only
         skip_pre_filter = implementation.lower() != "cpython"
-        registry_spec = PythonSpec(None, implementation, major, minor, None, arch, exe)
+        registry_spec = PythonSpec(None, implementation, major, minor, None, arch, exe, free_threaded=threaded)
         if skip_pre_filter or registry_spec.satisfies(spec):
             interpreter = Pep514PythonInfo.from_exe(exe, cache_dir, env=env, raise_on_error=False)
             if interpreter is not None and interpreter.satisfies(spec, impl_must_match=True):

src/virtualenv/discovery/windows/pep514.py

@@ -65,7 +65,8 @@ def process_tag(hive_name, company, company_key, tag, default_arch):
                 exe_data = load_exe(hive_name, company, company_key, tag)
                 if exe_data is not None:
                     exe, args = exe_data
-                    return company, major, minor, arch, exe, args
+                    threaded = load_threaded(hive_name, company, tag, tag_key)
+                    return company, major, minor, arch, threaded, exe, args
                 return None
             return None
         return None
@@ -138,6 +139,18 @@ def parse_version(version_str):
     raise ValueError(error)
 
 
+def load_threaded(hive_name, company, tag, tag_key):
+    display_name = get_value(tag_key, "DisplayName")
+    if display_name is not None:
+        if isinstance(display_name, str):
+            if "freethreaded" in display_name.lower():
+                return True
+        else:
+            key_path = f"{hive_name}/{company}/{tag}/DisplayName"
+            msg(key_path, f"display name is not string: {display_name!r}")
+    return bool(re.match(r"^\d+(\.\d+){0,2}t$", tag, flags=re.IGNORECASE))
+
+
 def msg(path, what):
     LOGGER.warning("PEP-514 violation in Windows Registry at %s error: %s", path, what)
 

tasks/pick_tox_env.py

@@ -8,5 +8,7 @@
 if py.startswith("brew@"):
     py = py[len("brew@") :]
 env = f"TOXENV={py}"
+if len(sys.argv) > 2:  # noqa: PLR2004
+    env += f"\nTOX_BASEPYTHON={sys.argv[2]}"
 with Path(os.environ["GITHUB_ENV"]).open("ta", encoding="utf-8") as file_handler:
     file_handler.write(env)

tests/integration/test_zipapp.py

@@ -26,23 +26,26 @@ def zipapp_build_env(tmp_path_factory):
         exe, found = None, False
         # prefer CPython as builder as pypy is slow
         for impl in ["cpython", ""]:
-            for version in range(11, 6, -1):
-                with suppress(Exception):
-                    # create a virtual environment which is also guaranteed to contain a recent enough pip (bundled)
-                    session = cli_run(
-                        [
-                            "-vvv",
-                            "-p",
-                            f"{impl}3.{version}",
-                            "--activators",
-                            "",
-                            str(create_env_path),
-                            "--no-download",
-                            "--no-periodic-update",
-                        ],
-                    )
-                    exe = str(session.creator.exe)
-                    found = True
+            for threaded in ["", "t"]:
+                for version in range(11, 6, -1):
+                    with suppress(Exception):
+                        # create a virtual environment which is also guaranteed to contain a recent enough pip (bundled)
+                        session = cli_run(
+                            [
+                                "-vvv",
+                                "-p",
+                                f"{impl}3.{version}{threaded}",
+                                "--activators",
+                                "",
+                                str(create_env_path),
+                                "--no-download",
+                                "--no-periodic-update",
+                            ],
+                        )
+                        exe = str(session.creator.exe)
+                        found = True
+                        break
+                if found:
                     break
             if found:
                 break

tests/unit/create/via_global_ref/builtin/cpython/cpython3_win_embed.json

@@ -57,5 +57,6 @@
   "system_stdlib": "c:\\path\\to\\python\\Lib",
   "system_stdlib_platform": "c:\\path\\to\\python\\Lib",
   "max_size": 9223372036854775807,
-  "_creators": null
+  "_creators": null,
+  "free_threaded": false
 }

tests/unit/create/via_global_ref/builtin/pypy/deb_pypy37.json

@@ -60,5 +60,6 @@
   "system_stdlib": "/usr/lib/pypy3/lib-python/3.7",
   "system_stdlib_platform": "/usr/lib/pypy3/lib-python/3.7",
   "max_size": 9223372036854775807,
-  "_creators": null
+  "_creators": null,
+  "free_threaded": false
 }

tests/unit/create/via_global_ref/builtin/pypy/deb_pypy38.json

@@ -60,5 +60,6 @@
   "system_stdlib": "/usr/lib/pypy3.8",
   "system_stdlib_platform": "/usr/lib/pypy3.8",
   "max_size": 9223372036854775807,
-  "_creators": null
+  "_creators": null,
+  "free_threaded": false
 }

tests/unit/create/via_global_ref/builtin/pypy/portable_pypy38.json

@@ -59,5 +59,6 @@
   "system_stdlib": "/tmp/pypy3.8-v7.3.8-linux64/lib/pypy3.8",
   "system_stdlib_platform": "/tmp/pypy3.8-v7.3.8-linux64/lib/pypy3.8",
   "max_size": 9223372036854775807,
-  "_creators": null
+  "_creators": null,
+  "free_threaded": false
 }