gh-79459 tempfile: Raise a ValueError if the prefix or suffix contains a directory component.

Lib/tempfile.py

@@ -119,11 +119,15 @@ def _sanitize_params(prefix, suffix, dir):
     output_type = _infer_return_type(prefix, suffix, dir)
     if suffix is None:
         suffix = output_type()
+    if _os.path.dirname(suffix):
+        raise ValueError("suffix can't contain a directory component")
     if prefix is None:
         if output_type is str:
             prefix = template
         else:
             prefix = _os.fsencode(template)
+    if _os.path.dirname(prefix):
+        raise ValueError("prefix can't contain a directory component")
     if dir is None:
         if output_type is str:
             dir = gettempdir()

Lib/test/test_tempfile.py

@@ -2154,5 +2154,46 @@ def test_cleanup_safe(self):
         # platforms, but don't forget to update the docs.
         self.assertTrue(tempfile._rmtree_use_dir_fd)
 
+
+class TestMisc(BaseTestCase):
+    def test_prefix_suffix_error(self):
+        tests = [
+            f"dir{os.sep}name",
+            f"{os.sep}abs_name",
+        ]
+        if os.altsep is not None:
+            tests.extend((
+                f"dir{os.altsep}name",
+                f"{os.altsep}abs_name",
+            ))
+        if support.MS_WINDOWS:
+            tests.append('C:name')
+        tests.extend(tuple(os.fsencode(path) for path in tests))
+
+        PREFIX_ERR = "prefix can't contain a directory component"
+        SUFFIX_ERR = "suffix can't contain a directory component"
+        for value in tests:
+            with self.subTest(value):
+                # test prefix
+                with self.assertRaisesRegex(ValueError, PREFIX_ERR):
+                    tempfile.mkstemp(prefix=value)
+                with self.assertRaisesRegex(ValueError, PREFIX_ERR):
+                    tempfile.mkdtemp(prefix=value)
+                with self.assertRaisesRegex(ValueError, PREFIX_ERR):
+                    tempfile.TemporaryFile(prefix=value)
+                with self.assertRaisesRegex(ValueError, PREFIX_ERR):
+                    tempfile.NamedTemporaryFile(prefix=value)
+
+                # test suffix
+                with self.assertRaisesRegex(ValueError, SUFFIX_ERR):
+                    tempfile.mkstemp(suffix=value)
+                with self.assertRaisesRegex(ValueError, SUFFIX_ERR):
+                    tempfile.mkdtemp(suffix=value)
+                with self.assertRaisesRegex(ValueError, SUFFIX_ERR):
+                    tempfile.TemporaryFile(suffix=value)
+                with self.assertRaisesRegex(ValueError, SUFFIX_ERR):
+                    tempfile.NamedTemporaryFile(suffix=value)
+
+
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS.d/next/Library/2026-10-05-13-57-08.gh-issue-79459.2RgBDL.rst

@@ -0,0 +1,2 @@
+:mod:`tempfile` functions that take a ``prefix`` or ``suffix`` argument now raise a :exc:`ValueError` if they contain a directory component:
+:func:`tempfile.mkstemp`, :func:`tempfile.mkdtemp`, :func:`tempfile.TemporaryFile`, :func:`tempfile.NamedTemporaryFile`.