From ca04d8930a2c382bc0bae37e87d1bd9e6a9d7d5a Mon Sep 17 00:00:00 2001
From: tangyuan0821 <tangyuan0821@email.cn>
Date: Mon, 22 Jun 2026 10:35:48 +0800
Subject: [PATCH 1/2] gh-130821: Add type info to error messages for __len__
 and __sizeof__

---
 Objects/typeobject.c | 4 ++--
 Python/sysmodule.c   | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 59593fd0f6a0b7..8abc1148064c7b 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -10625,8 +10625,8 @@ slot_sq_length(PyObject *self)
     assert(PyLong_Check(res));
     if (_PyLong_IsNegative((PyLongObject *)res)) {
         Py_DECREF(res);
-        PyErr_SetString(PyExc_ValueError,
-                        "__len__() should return >= 0");
+        PyErr_Format(PyExc_ValueError,
+                        "%T.__len__() must return >= 0", self);
         return -1;
     }
 
diff --git a/Python/sysmodule.c b/Python/sysmodule.c
index d9f7b9c449cfb9..6dd593e5340ccf 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -1933,8 +1933,8 @@ _PySys_GetSizeOf(PyObject *o)
         return (size_t)-1;
 
     if (size < 0) {
-        _PyErr_SetString(tstate, PyExc_ValueError,
-                          "__sizeof__() should return >= 0");
+        _PyErr_Format(tstate, PyExc_ValueError,
+                          "%T.__sizeof__() must return >= 0", o);
         return (size_t)-1;
     }
 

From abf13a8cd56177abace9730472646977f8e27e47 Mon Sep 17 00:00:00 2001
From: tangyuan0821 <tangyuan0821@email.cn>
Date: Mon, 22 Jun 2026 10:42:12 +0800
Subject: [PATCH 2/2] gh-130821: Add news entry for __len__ and __sizeof__
 error message fix

---
 .../2026-06-22-10-39-56.gh-issue-130821.b5e011.rst              | 2 ++
 1 file changed, 2 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Core_and_Builtins/2026-06-22-10-39-56.gh-issue-130821.b5e011.rst

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-06-22-10-39-56.gh-issue-130821.b5e011.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-06-22-10-39-56.gh-issue-130821.b5e011.rst
new file mode 100644
index 00000000000000..1f6bed1965ae2b
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2026-06-22-10-39-56.gh-issue-130821.b5e011.rst
@@ -0,0 +1,2 @@
+Add type information to error messages for ``__len__()`` and ``__sizeof__()``.
+Patch by tangyuan0821.