Support PATHEXT extension that ends with a dot.

Lib/shutil.py

@@ -1551,7 +1551,7 @@ def which(cmd, mode=os.F_OK | os.X_OK, path=None):
         # PATHEXT is necessary to check on Windows.
         pathext_source = os.getenv("PATHEXT") or _WIN_DEFAULT_PATHEXT
         pathext = pathext_source.split(os.pathsep)
-        pathext = [ext.rstrip('.') and ext for ext in pathext if ext]
+        pathext = [ext.rstrip('.') for ext in pathext if ext]
 
         if use_bytes:
             pathext = [os.fsencode(ext) for ext in pathext]

Lib/test/test_shutil.py

@@ -2546,6 +2546,21 @@ def test_pathext_with_null_extension(self):
             self.assertEqual(shutil.which(cmddot, path=self.dir),
                              filepath + self.to_text_type('.'))
 
+    @unittest.skipUnless(sys.platform == "win32", 'test specific to Windows')
+    def test_pathext_extension_ends_with_dot(self):
+        ext = '.xyz'
+        cmd = self.to_text_type(TESTFN2)
+        cmdext = cmd + self.to_text_type(ext)
+        dot = self.to_text_type('.')
+        filepath = os.path.join(self.dir, cmdext)
+        self.create_file(filepath)
+        with os_helper.EnvironmentVarGuard() as env:
+            env['PATHEXT'] = ext + '.'
+            self.assertEqual(shutil.which(cmd, path=self.dir), filepath)  # cmd.exe hangs here
+            self.assertEqual(shutil.which(cmdext, path=self.dir), filepath)
+            self.assertIsNone(shutil.which(cmd + dot, path=self.dir))
+            self.assertIsNone(shutil.which(cmdext + dot, path=self.dir))
+
     # See GH-75586
     @unittest.skipUnless(sys.platform == "win32", 'test specific to Windows')
     def test_pathext_applied_on_files_in_path(self):

Misc/NEWS.d/next/Library/2024-11-22-10-42-34.gh-issue-127035.UnbDlr.rst

@@ -1,3 +1,4 @@
 Fix :mod:`shutil.which` on Windows. Now it looks at direct match if and only
 if the command ends with a PATHEXT extension or X_OK is not in mode. Support
-extensionless files if "." is in PATHEXT.
+extensionless files if "." is in PATHEXT. Support PATHEXT extensions that end
+with a dot.