diff --git a/Doc/tutorial/datastructures.rst b/Doc/tutorial/datastructures.rst
index db8a066b369a830..1332c53f39687ec 100644
--- a/Doc/tutorial/datastructures.rst
+++ b/Doc/tutorial/datastructures.rst
@@ -512,8 +512,12 @@ dictionary; this is also the way dictionaries are written on output.
 The main operations on a dictionary are storing a value with some key and
 extracting the value given the key.  It is also possible to delete a key:value
 pair with ``del``. If you store using a key that is already in use, the old
-value associated with that key is forgotten.  It is an error to extract a value
-using a non-existent key.
+value associated with that key is forgotten.
+
+Extracting a value for a non-existent key by subscripting (``d[key]``) raises a
+:exc:`KeyError`. To avoid getting this error when trying to access a possibly
+non-existent key, use the :meth:`~dict.get` method instead, which returns
+``None`` (or a specified default value) if the key is not in the dictionary.
 
 Performing ``list(d)`` on a dictionary returns a list of all the keys
 used in the dictionary, in insertion order (if you want it sorted, just use
@@ -528,6 +532,12 @@ Here is a small example using a dictionary::
    {'jack': 4098, 'sape': 4139, 'guido': 4127}
    >>> tel['jack']
    4098
+   >>> tel['irv']
+   Traceback (most recent call last):
+     File "<stdin>", line 1, in <module>
+   KeyError: 'irv'
+   >>> print(tel.get('irv'))
+   None
    >>> del tel['sape']
    >>> tel['irv'] = 4127
    >>> tel
diff --git a/Lib/test/test_inspect/test_inspect.py b/Lib/test/test_inspect/test_inspect.py
index 555efb78dcc6aab..e32e34c63b53246 100644
--- a/Lib/test/test_inspect/test_inspect.py
+++ b/Lib/test/test_inspect/test_inspect.py
@@ -4261,8 +4261,14 @@ def __init__(self, a):
 
             self.assertEqual(self.signature(C, follow_wrapped=False),
                              varargs_signature)
-            self.assertEqual(self.signature(C.__new__, follow_wrapped=False),
-                             varargs_signature)
+            if support.MISSING_C_DOCSTRINGS:
+                self.assertRaisesRegex(
+                    ValueError, "no signature found",
+                    self.signature, C.__new__, follow_wrapped=False,
+                )
+            else:
+                self.assertEqual(self.signature(C.__new__, follow_wrapped=False),
+                                varargs_signature)
 
     def test_signature_on_class_with_wrapped_new(self):
         with self.subTest('FunctionType'):
diff --git a/Lib/test/test_peg_generator/test_c_parser.py b/Lib/test/test_peg_generator/test_c_parser.py
index aa01a9b8f7ed87f..395f15b9a62cdfc 100644
--- a/Lib/test/test_peg_generator/test_c_parser.py
+++ b/Lib/test/test_peg_generator/test_c_parser.py
@@ -100,11 +100,15 @@ def setUpClass(cls):
 
         with contextlib.ExitStack() as stack:
             python_exe = stack.enter_context(support.setup_venv_with_pip_setuptools("venv"))
-            sitepackages = subprocess.check_output(
+            platlib_path = subprocess.check_output(
                 [python_exe, "-c", "import sysconfig; print(sysconfig.get_path('platlib'))"],
                 text=True,
             ).strip()
-            stack.enter_context(import_helper.DirsOnSysPath(sitepackages))
+            purelib_path = subprocess.check_output(
+                [python_exe, "-c", "import sysconfig; print(sysconfig.get_path('purelib'))"],
+                text=True,
+            ).strip()
+            stack.enter_context(import_helper.DirsOnSysPath(platlib_path, purelib_path))
             cls.addClassCleanup(stack.pop_all().close)
 
     @support.requires_venv_with_pip()
diff --git a/Lib/test/test_pydoc/test_pydoc.py b/Lib/test/test_pydoc/test_pydoc.py
index 65ad7649b9e2dba..5aa8d92057e3d70 100644
--- a/Lib/test/test_pydoc/test_pydoc.py
+++ b/Lib/test/test_pydoc/test_pydoc.py
@@ -1902,7 +1902,7 @@ def test_text_doc_routines_in_class(self, cls=pydocfodder.B):
         else:
             self.assertIn(' |  get(...) method of builtins.dict instance', lines)
             self.assertIn(' |  dict_get = get(...) method of builtins.dict instance', lines)
-            self.assertIn(' |  sin(...)', lines)
+            self.assertIn(' |  sin(object, /)', lines)
 
         lines = self.getsection(result, f' |  Class methods {where}:', ' |  ' + '-'*70)
         self.assertIn(' |  B_classmethod(x)', lines)
@@ -1992,7 +1992,7 @@ def test_text_doc_routines_in_module(self):
         if not support.MISSING_C_DOCSTRINGS:
             self.assertIn('    sin(x, /)', lines)
         else:
-            self.assertIn('    sin(...)', lines)
+            self.assertIn('    sin(object, /)', lines)
 
     def test_html_doc_routines_in_module(self):
         doc = pydoc.HTMLDoc()
@@ -2037,7 +2037,7 @@ def test_html_doc_routines_in_module(self):
         if not support.MISSING_C_DOCSTRINGS:
             self.assertIn(' sin(x, /)', lines)
         else:
-            self.assertIn(' sin(...)', lines)
+            self.assertIn(' sin(object, /)', lines)
 
 
 @unittest.skipIf(
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-09-29-00-01-28.gh-issue-139400.X2T-jO.rst b/Misc/NEWS.d/next/Security/2025-09-29-00-01-28.gh-issue-139400.X2T-jO.rst
similarity index 100%
rename from Misc/NEWS.d/next/Core_and_Builtins/2025-09-29-00-01-28.gh-issue-139400.X2T-jO.rst
rename to Misc/NEWS.d/next/Security/2025-09-29-00-01-28.gh-issue-139400.X2T-jO.rst