Behavior updated from pr comments

Doc/library/shutil.rst

@@ -477,9 +477,9 @@ Directory and files operations
       have no extension can now be found.
 
    .. versionchanged:: 3.12.1
-      On Windows, if *mode* includes ``os.X_OK``, only executables with an
-      extension in ``PATHEXT`` will be returned. Therefore extension-less
-      files cannot be returned by :func:`shutil.which` by default on Windows.
+      On Windows, if *mode* includes ``os.X_OK``, executables with an
+      extension in ``PATHEXT`` will be preferred over executables without a
+      matching extension.
       This brings behavior closer to that of Python 3.11.
 
 .. exception:: Error

Lib/shutil.py

@@ -1560,9 +1560,10 @@ def which(cmd, mode=os.F_OK | os.X_OK, path=None):
         # for a PATHEXT match. The first cmd is the direct match
         # (e.g. python.exe instead of python)
         # Check that direct match first if and only if the extension is in PATHEXT
+        # Otherwise check it last
         suffix = os.path.splitext(files[0])[1].upper()
         if mode & os.X_OK and not any(suffix == ext.upper() for ext in pathext):
-            del files[0]
+            files.append(files.pop(0))
     else:
         # On other platforms you don't have things like PATHEXT to tell you
         # what file suffixes are executable, so just pass on cmd as-is.

Lib/test/test_shutil.py

@@ -2323,7 +2323,7 @@ def test_win_path_needs_curdir(self):
 
     # See GH-109590
     @unittest.skipUnless(sys.platform == "win32", 'test specific to Windows')
-    def test_pathext_enforced_for_execute(self):
+    def test_pathext_preferred_for_execute(self):
         with os_helper.EnvironmentVarGuard() as env:
             env["PATH"] = self.temp_dir if isinstance(self.temp_dir, str) else self.temp_dir.decode()
             env["PATHEXT"] = ".test"
@@ -2332,10 +2332,18 @@ def test_pathext_enforced_for_execute(self):
             open(exe, 'w').close()
             os.chmod(exe, 0o755)
 
-            # default does not match since .exe is not in PATHEXT
-            self.assertIsNone(shutil.which(self.to_text_type("test.exe")))
+            # default behavior allows a direct match if nothing in PATHEXT matches
+            self.assertEqual(shutil.which(self.to_text_type("test.exe")), exe)
+
+            dot_test = os.path.join(self.temp_dir, self.to_text_type("test.exe.test"))
+            open(dot_test, 'w').close()
+            os.chmod(dot_test, 0o755)
 
-            # but if we don't use os.X_OK we're ok not matching PATHEXT
+            # now we have a PATHEXT match, so it take precedence
+            self.assertEqual(shutil.which(self.to_text_type("test.exe")), dot_test)
+
+            # but if we don't use os.X_OK we don't change the order based off PATHEXT
+            # and therefore get the direct match.
             self.assertEqual(shutil.which(self.to_text_type("test.exe"), mode=os.F_OK), exe)
 
     # See GH-109590
@@ -2355,7 +2363,6 @@ def test_pathext_given_extension_preferred(self):
 
             # even though .exe2 is preferred in PATHEXT, we matched directly to test.exe
             self.assertEqual(shutil.which(self.to_text_type("test.exe")), exe)
-
             self.assertEqual(shutil.which(self.to_text_type("test")), exe2)
 
 

Misc/NEWS.d/next/Library/2023-09-24-06-04-14.gh-issue-109590.9EMofC.rst

@@ -1,2 +1,3 @@
-:func:`shutil.which` will only match files with an extension in ``PATHEXT`` if the given mode includes ``os.X_OK`` on win32.
+:func:`shutil.which` will prefer files with an extension in ``PATHEXT`` if the given mode includes ``os.X_OK`` on win32.
+If no ``PATHEXT`` match is found, a file without an extension in ``PATHEXT`` can be returned.
 This change will have :func:`shutil.which` act more similarly to previous behavior in Python 3.11.