python · srittau · May 13, 2025 · May 13, 2025
diff --git a/lib/ts_utils/metadata.py b/lib/ts_utils/metadata.py
@@ -47,7 +47,7 @@ def _is_nested_dict(obj: object) -> TypeGuard[dict[str, dict[str, Any]]]:
 
 
 @functools.cache
-def _get_oldest_supported_python() -> str:
+def get_oldest_supported_python() -> str:
     with PYPROJECT_PATH.open("rb") as config:
         val = tomli.load(config)["tool"]["typeshed"]["oldest_supported_python"]
     assert type(val) is str
@@ -276,7 +276,7 @@ def read_metadata(distribution: str) -> StubMetadata:
     partial_stub: object = data.get("partial_stub", True)
     assert type(partial_stub) is bool
     requires_python_str: object = data.get("requires_python"
8000
;)
-    oldest_supported_python = _get_oldest_supported_python()
+    oldest_supported_python = get_oldest_supported_python()
     oldest_supported_python_specifier = Specifier(f">={oldest_supported_python}")
     if requires_python_str is None:
         requires_python = oldest_supported_python_specifier

diff --git a/tests/runtests.py b/tests/runtests.py
@@ -9,6 +9,7 @@
 from importlib.util import find_spec
 from pathlib import Path
 
+from ts_utils.metadata import get_oldest_supported_python, read_metadata
 from ts_utils.paths import TEST_CASES_DIR, test_cases_path
 from ts_utils.utils import colored
 
@@ -19,9 +20,6 @@
 _SUCCESS = colored("Success", "green")
 _SKIPPED = colored("Skipped", "yellow")
 _FAILED = colored("Failed", "red")
-# We're using the oldest fully supported version because it's the most likely to produce errors
-# due to unsupported syntax, feature, or bug in a tool.
-_PYTHON_VERSION = "3.9"
 
 
 def _parse_jsonc(json_text: str) -> str:
@@ -52,15 +50,16 @@ def main() -> None:
     )
     parser.add_argument(
         "--python-version",
-        default=_PYTHON_VERSION,
+        default=None,
         choices=("3.9", "3.10", "3.11", "3.12", "3.13", "3.14"),
-        help="Target Python version for the test (default: %(default)s).",
+        # We're using the oldest fully supported version because it's the most likely to produce errors
+        # due to unsupported syntax, feature, or bug in a tool.
+        help="Target Python version for the test (defaults to oldest supported Python version).",
     )
     parser.add_argument("path", help="Path of the stub to test in format <folder>/<stub>, from the root of the project.")
     args = parser.parse_args()
     path = Path(args.path)
     run_stubtest: bool = args.run_stubtest
-    python_version: str = args.python_version
 
     if len(path.parts) != 2:
         parser.error("'path' argument should be in format <folder>/<stub>.")
@@ -69,6 +68,14 @@ def main() -> None:
         parser.error("Only the 'stdlib' and 'stubs' folders are supported.")
     if not path.exists():
         parser.error(f"{path=} does not exist.")
+
+    if args.python_version:
+        python_version: str = args.python_version
+    elif folder in "stubs":
+        python_version = read_metadata(stub).requires_python.version
+    else:
+        python_version = get_oldest_supported_python()
+
     stubtest_result: subprocess.CompletedProcess[bytes] | None = None
     pytype_result: subprocess.CompletedProcess[bytes] | None = None