Make sure isinstance(typing_extensions.ParamSpec("P"), typing.TypeVar) is unaffected by sys.setprofile()

.github/workflows/publish.yml

@@ -92,8 +92,8 @@ jobs:
  export path_to_file=$(find dist -type f -name "typing_extensions-*.tar.gz")
  echo "::notice::Unpacking source distribution: $path_to_file"
  tar xzf $path_to_file -C dist/
- cd ${path_to_file%.tar.gz}
- python src/test_typing_extensions.py
+ cd ${path_to_file%.tar.gz}/src
+ python test_typing_extensions.py
 
  test-sdist-installed:
  name: Test installed source distribution

CHANGELOG.md

@@ -1,3 +1,11 @@
+# Unreleased
+
+- Fix incorrect behaviour of `typing_extensions.ParamSpec` on Python 3.8 and
+ 3.9 that meant that
+ `isinstance(typing_extensions.ParamSpec("P"), typing.TypeVar)` would have a
+ different result in some situations depending on whether or not a profiling
+ function had been set using `sys.setprofile`. Patch by Alex Waygood.
+
 # Release 4.12.0rc1 (May 16, 2024)
 
 This release focuses on compatibility with the upcoming release of

src/test_typing_extensions.py

@@ -5020,6 +5020,48 @@ def test_eq(self):
  # won't be the same.
  self.assertNotEqual(hash(ParamSpec('P')), hash(P))
 
+ def test_isinstance_results_unaffected_by_presence_of_tracing_function(self):
+ # See https://github.com/python/typing_extensions/issues/318
+
+ code = textwrap.dedent(
+ """\
+ import sys, typing
+
+ def trace_call(*args):
+ return trace_call
+
+ def run():
+ sys.modules.pop("typing_extensions", None)
+ from typing_extensions import ParamSpec
+ return isinstance(ParamSpec("P"), typing.TypeVar)
+
+ isinstance_result_1 = run()
+ sys.setprofile(trace_call)
+ isinstance_result_2 = run()
+ sys.stdout.write(f"{isinstance_result_1} {isinstance_result_2}")
+ """
+ )
+
+ # Run this in an isolated process or it pollutes the environment
+ # and makes other tests fail:
+ try:
+ proc = subprocess.run(
+ [sys.executable, "-c", code], check=True, capture_output=True, text=True,
+ )
+ except subprocess.CalledProcessError as exc:
+ print("stdout", exc.stdout, sep="\n")
+ print("stderr", exc.stderr, sep="\n")
+ raise
+
+ # Sanity checks that assert the test is working as expected
+ self.assertIsInstance(proc.stdout, str)
+ result1, result2 = proc.stdout.split(" ")
+ self.assertIn(result1, {"True", "False"})
+ self.assertIn(result2, {"True", "False"})
+
+ # The actual test:
+ self.assertEqual(result1, result2)
+
 
 class ConcatenateTests(BaseTestCase):
  def test_basics(self):

src/typing_extensions.py

@@ -1711,7 +1711,7 @@ def kwargs(self):
 
  def __init__(self, name, *, bound=None, covariant=False, contravariant=False,
  infer_variance=False, default=NoDefault):
-super().__init__([self])
+list.__init__(self, [self])
  self.__name__ = name
  self.__covariant__ = bool(covariant)
  self.__contravariant__ = bool(contravariant)