diff --git a/Lib/shutil.py b/Lib/shutil.py
index 1f05d80f32a8fc..9d151493e76675 100644
--- a/Lib/shutil.py
+++ b/Lib/shutil.py
@@ -53,6 +53,9 @@
_USE_CP_SENDFILE = hasattr(os, "sendfile") and sys.platform.startswith("linux")
_HAS_FCOPYFILE = posix and hasattr(posix, "_fcopyfile") # macOS
+# CMD defaults in Windows 10
+_WIN_DEFAULT_PATHEXT = ".COM;.EXE;.BAT;.CMD;.VBS;.JS;.WS;.MSC"
+
__all__ = ["copyfileobj", "copyfile", "copymode", "copystat", "copy", "copy2",
"copytree", "move", "rmtree", "Error", "SpecialFileError",
"ExecError", "make_archive", "get_archive_formats",
@@ -1400,7 +1403,9 @@ def which(cmd, mode=os.F_OK | os.X_OK, path=None):
path.insert(0, curdir)
# PATHEXT is necessary to check on Windows.
- pathext = os.environ.get("PATHEXT", "").split(os.pathsep)
+ pathext_source = os.getenv("PATHEXT") or _WIN_DEFAULT_PATHEXT
+ pathext = [ext for ext in pathext_source.split(os.pathsep) if ext]
+
if use_bytes:
pathext = [os.fsencode(ext) for ext in pathext]
# See if the given file matches any of the expected path extensions.
diff --git a/Lib/test/test_shutil.py b/Lib/test/test_shutil.py
index bcb7e498e198e2..77306170d9fc18 100644
--- a/Lib/test/test_shutil.py
+++ b/Lib/test/test_shutil.py
@@ -1830,6 +1830,23 @@ def test_pathext(self):
rv = shutil.which(program, path=self.temp_dir)
self.assertEqual(rv, temp_filexyz.name)
+ # Issue 40592: See https://bugs.python.org/issue40592
+ @unittest.skipUnless(sys.platform == "win32", 'test specific to Windows')
+ def test_pathext_with_empty_str(self):
+ ext = ".xyz"
+ temp_filexyz = tempfile.NamedTemporaryFile(dir=self.temp_dir,
+ prefix="Tmp2", suffix=ext)
+ self.addCleanup(temp_filexyz.close)
+
+ # strip path and extension
+ program = os.path.basename(temp_filexyz.name)
+ program = os.path.splitext(program)[0]
+
+ with support.EnvironmentVarGuard() as env:
+ env['PATHEXT'] = f"{ext};" # note the ;
+ rv = shutil.which(program, path=self.temp_dir)
+ self.assertEqual(rv, temp_filexyz.name)
+
class TestWhichBytes(TestWhich):
def setUp(self):
diff --git a/Misc/NEWS.d/next/Library/2020-05-14-16-01-34.bpo-40592.Cmk855.rst b/Misc/NEWS.d/next/Library/2020-05-14-16-01-34.bpo-40592.Cmk855.rst
new file mode 100644
index 00000000000000..3211a1bc345fa5
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-05-14-16-01-34.bpo-40592.Cmk855.rst
@@ -0,0 +1 @@
+:func:`shutil.which` now ignores empty entries in :envvar:`PATHEXT` instead of treating them as a match.
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