gh-154610: Use repr() to format the attribute name in AttributeError

Lib/_pydecimal.py

@@ -3953,7 +3953,7 @@ def __setattr__(self, name, value):
             return object.__setattr__(self, name, value)
         else:
             raise AttributeError(
-                "'decimal.Context' object has no attribute '%s'" % name)
+                f"'decimal.Context' object has no attribute {name!r}")
 
     def __delattr__(self, name):
         raise AttributeError("%s cannot be deleted" % name)

Lib/calendar.py

@@ -54,7 +54,7 @@ def __getattr__(name):
         else:
             return 2
 
-    raise AttributeError(f"module '{__name__}' has no attribute '{name}'")
+    raise AttributeError(f"module '{__name__}' has no attribute {name!r}")
 
 
 # Constants for months

Lib/enum.py

@@ -190,9 +190,8 @@ def __get__(self, instance, ownerclass=None):
             if self.member is not None:
                 return self.member
             else:
-                raise AttributeError(
-                        '%r has no attribute %r' % (ownerclass, self.name)
-                        )
+                errmsg = f'{ownerclass!r} has no attribute {self.name!r}'
+                raise AttributeError(errmsg)
         if self.fget is not None:
             # use previous enum.property
             return self.fget(instance)
@@ -206,9 +205,8 @@ def __get__(self, instance, ownerclass=None):
         try:
             return ownerclass._member_map_[self.name]
         except KeyError:
-            raise AttributeError(
-                    '%r has no attribute %r' % (ownerclass, self.name)
-                    ) from None
+            errmsg = f'{ownerclass!r} has no attribute {self.name!r}'
+            raise AttributeError(errmsg) from None
 
     def __set__(self, instance, value):
         if self.fset is not None:

Lib/test/test_builtin.py

@@ -1226,6 +1226,10 @@ def test_getattr(self):
         self.assertRaises(AttributeError, getattr, sys, chr(sys.maxunicode))
         # unicode surrogates are not encodable to the default encoding (utf8)
         self.assertRaises(AttributeError, getattr, 1, "\uDAD1\uD51E")
+        with self.assertRaises(AttributeError) as cm:
+            getattr(object(), "a'b")
+        self.assertEqual(str(cm.exception),
+                         ''''object' object has no attribute "a'b"''')
 
     def test_hasattr(self):
         self.assertTrue(hasattr(sys, 'stdout'))
@@ -2155,6 +2159,15 @@ def test_setattr(self):
         msg = r"^attribute name must be string, not 'int'$"
         self.assertRaisesRegex(TypeError, msg, setattr, sys, 1, 'spam')
 
+        class A:
+            __slots__ = ()
+
+        with self.assertRaises(AttributeError) as cm:
+            setattr(object(), "a'b", 1)
+        self.assertEqual(str(cm.exception),
+                         """'object' object has no attribute "a'b" """
+                         "and no __dict__ for setting new attributes")
+
     # test_str(): see test_str.py and test_bytes.py for str() tests.
 
     def test_sum(self):

Lib/test/test_decimal.py

@@ -3695,6 +3695,19 @@ def test_to_integral_value(self):
         self.assertRaises(TypeError, c.to_integral_value, '10')
         self.assertRaises(TypeError, c.to_integral_value, 10, 'x')
 
+    def test_setattr(self):
+        Context = self.decimal.Context
+
+        ctx = Context()
+        ctx.prec = 123
+        with self.assertRaises(AttributeError):
+            ctx.xyz = 1
+        with self.assertRaises(AttributeError) as cm:
+            setattr(ctx, "a'b", 1)
+        self.assertEqual(str(cm.exception),
+                         ''''decimal.Context' object has no attribute "a'b"''')
+
+
 @requires_cdecimal
 class CContextAPItests(ContextAPItests, unittest.TestCase):
     decimal = C

Lib/test/test_module/__init__.py

@@ -47,6 +47,9 @@ def test_missing_getattr(self):
         self.assertRaisesRegex(
                 AttributeError, "module 'foo' has no attribute 'not_here'",
                 getattr, foo, "not_here")
+        self.assertRaisesRegex(
+                AttributeError, '''module 'foo' has no attribute "a'b"''',
+                getattr, foo, "a'b")
 
     def test_no_docstring(self):
         # Regularly initialized module, no docstring

Lib/test/test_unittest/test_case.py

@@ -796,6 +796,10 @@ def testAssertHasAttr(self):
             self.assertHasAttr(a, 'y')
         self.assertEqual(str(cm.exception),
                 "'List' object has no attribute 'y'")
+        with self.assertRaises(self.failureException) as cm:
+            self.assertHasAttr(a, "a'b")
+        self.assertEqual(str(cm.exception),
+                ''''List' object has no attribute "a'b"''')
         with self.assertRaises(self.failureException) as cm:
             self.assertHasAttr(List, 'spam')
         self.assertEqual(str(cm.exception),

Lib/test/test_unittest/testmock/testmock.py

@@ -685,6 +685,11 @@ def test_attributes(mock):
                 "Mock object has no attribute 'z'",
                 getattr, mock, 'z'
             )
+            self.assertRaisesRegex(
+                AttributeError,
+                '''Mock object has no attribute "a'b"''',
+                getattr, mock, "a'b"
+            )
             self.assertRaisesRegex(
                 AttributeError,
                 "Mock object has no attribute '__foobar__'",

Lib/unittest/mock.py

@@ -808,13 +808,13 @@ def __setattr__(self, name, value):
         elif (self._spec_set and self._mock_methods is not None and
             name not in self._mock_methods and
             name not in self.__dict__):
-            raise AttributeError("Mock object has no attribute '%s'" % name)
+            raise AttributeError(f"Mock object has no attribute {name!r}")
         elif name in _unsupported_magics:
-            msg = 'Attempting to set unsupported magic method %r.' % name
+            msg = f'Attempting to set unsupported magic method {name!r}.'
             raise AttributeError(msg)
         elif name in _all_magics:
             if self._mock_methods is not None and name not in self._mock_methods:
-                raise AttributeError("Mock object has no attribute '%s'" % name)
+                raise AttributeError(f"Mock object has no attribute {name!r}")
 
             if not _is_instance_mock(value):
                 setattr(type(self), name, _get_method(name, value))

Misc/NEWS.d/next/Core_and_Builtins/2026-07-24-15-50-43.gh-issue-154610.t5PtGH.rst

@@ -0,0 +1,4 @@
+Format the attribute name with :func:`repr`, instead of :func:`str`, when
+formatting :exc:`AttributeError` error message. For example,
+``getattr(object(), "a'b")`` now formats the attribute error correctly.
+Patch by Victor Stinner.

Objects/dictobject.c

@@ -7497,7 +7497,7 @@ store_instance_attr_lock_held(PyObject *obj, PyDictValues *values,
     PyObject *old_value = values->values[ix];
     if (old_value == NULL && value == NULL) {
         PyErr_Format(PyExc_AttributeError,
-                        "'%.100s' object has no attribute '%U'",
+                        "'%s' object has no attribute %R",
                         Py_TYPE(obj)->tp_name, name);
         (void)_PyObject_SetAttributeErrorContext(obj, name);
         return -1;

Objects/funcobject.c

@@ -1361,7 +1361,7 @@ descriptor_set_wrapped_attribute(PyObject *oobj, PyObject *name, PyObject *value
             if (PyErr_ExceptionMatches(PyExc_KeyError)) {
                 PyErr_Clear();
                 PyErr_Format(PyExc_AttributeError,
-                             "'%.200s' object has no attribute '%U'",
+                             "'%s' object has no attribute %R",
                              type_name, name);
                 Py_DECREF(dict);
                 return -1;

Objects/moduleobject.c

@@ -1422,7 +1422,7 @@ _Py_module_getattro_impl(PyModuleObject *m, PyObject *name, int suppress)
     if (!mod_name || !PyUnicode_Check(mod_name)) {
         Py_XDECREF(mod_name);
         PyErr_Format(PyExc_AttributeError,
-                    "module has no attribute '%U'", name);
+                    "module has no attribute %R", name);
         return NULL;
     }
     PyObject *spec;
@@ -1432,7 +1432,7 @@ _Py_module_getattro_impl(PyModuleObject *m, PyObject *name, int suppress)
     }
     if (spec == NULL) {
         PyErr_Format(PyExc_AttributeError,
-                     "module '%U' has no attribute '%U'",
+                     "module '%U' has no attribute %R",
                      mod_name, name);
         Py_DECREF(mod_name);
         return NULL;
@@ -1466,9 +1466,9 @@ _Py_module_getattro_impl(PyModuleObject *m, PyObject *name, int suppress)
     if (is_possibly_shadowing_stdlib) {
         assert(origin);
         PyErr_Format(PyExc_AttributeError,
-                    "module '%U' has no attribute '%U' "
-                    "(consider renaming '%U' since it has the same "
-                    "name as the standard library module named '%U' "
+                    "module %R has no attribute %R "
+                    "(consider renaming %R since it has the same "
+                    "name as the standard library module named %R "
                     "and prevents importing that standard library module)",
                     mod_name, name, origin, mod_name);
     }
@@ -1483,22 +1483,22 @@ _Py_module_getattro_impl(PyModuleObject *m, PyObject *name, int suppress)
                 // For non-stdlib modules, only mention the possibility of
                 // shadowing if the module is being initialized.
                 PyErr_Format(PyExc_AttributeError,
-                            "module '%U' has no attribute '%U' "
-                            "(consider renaming '%U' if it has the same name "
+                            "module %R has no attribute %R "
+                            "(consider renaming %R if it has the same name "
                             "as a library you intended to import)",
                             mod_name, name, origin);
             }
             else if (origin) {
                 PyErr_Format(PyExc_AttributeError,
                             "partially initialized "
-                            "module '%U' from '%U' has no attribute '%U' "
+                            "module %R from %R has no attribute %R "
                             "(most likely due to a circular import)",
                             mod_name, origin, name);
             }
             else {
                 PyErr_Format(PyExc_AttributeError,
                             "partially initialized "
-                            "module '%U' has no attribute '%U' "
+                            "module %R has no attribute %R "
                             "(most likely due to a circular import)",
                             mod_name, name);
             }
@@ -1514,7 +1514,7 @@ _Py_module_getattro_impl(PyModuleObject *m, PyObject *name, int suppress)
             }
             else if (rc == 0) {
                 PyErr_Format(PyExc_AttributeError,
-                            "module '%U' has no attribute '%U'",
+                            "module %R has no attribute %R",
                             mod_name, name);
             }
         }

Objects/object.c

@@ -1330,7 +1330,7 @@ PyObject_GetAttr(PyObject *v, PyObject *name)
     }
     else {
         PyErr_Format(PyExc_AttributeError,
-                    "'%.100s' object has no attribute '%U'",
+                    "'%s' object has no attribute %R",
                     tp->tp_name, name);
     }
 
@@ -1377,7 +1377,7 @@ _PyObject_GetAttrStackRef(PyObject *v, PyObject *name)
     }
     else {
         PyErr_Format(PyExc_AttributeError,
-                    "'%.100s' object has no attribute '%U'",
+                    "'%s' object has no attribute %R",
                     tp->tp_name, name);
     }
 
@@ -1548,14 +1548,14 @@ PyObject_SetAttr(PyObject *v, PyObject *name, PyObject *value)
     _PyObject_ASSERT(name, Py_REFCNT(name) >= 1);
     if (tp->tp_getattr == NULL && tp->tp_getattro == NULL)
         PyErr_Format(PyExc_TypeError,
-                     "'%.100s' object has no attributes "
+                     "'%s' object has no attributes "
                      "(%s .%U)",
                      tp->tp_name,
                      value==NULL ? "del" : "assign to",
                      name);
     else
         PyErr_Format(PyExc_TypeError,
-                     "'%.100s' object has only read-only attributes "
+                     "'%s' object has only read-only attributes "
                      "(%s .%U)",
                      tp->tp_name,
                      value==NULL ? "del" : "assign to",
@@ -1737,7 +1737,7 @@ _PyObject_GetMethod(PyObject *obj, PyObject *name, PyObject **method)
     }
 
     PyErr_Format(PyExc_AttributeError,
-                 "'%.100s' object has no attribute '%U'",
+                 "'%s' object has no attribute %R",
                  tp->tp_name, name);
 
     _PyObject_SetAttributeErrorContext(obj, name);
@@ -1871,7 +1871,7 @@ _PyObject_GetMethodStackRef(PyThreadState *ts, _PyStackRef *self,
     }
 
     PyErr_Format(PyExc_AttributeError,
-                 "'%.100s' object has no attribute '%U'",
+                 "'%s' object has no attribute %R",
                  tp->tp_name, name);
 
     _PyObject_SetAttributeErrorContext(obj, name);
@@ -1995,7 +1995,7 @@ _PyObject_GenericGetAttrWithDict(PyObject *obj, PyObject *name,
 
     if (!suppress) {
         PyErr_Format(PyExc_AttributeError,
-                     "'%.100s' object has no attribute '%U'",
+                     "'%s' object has no attribute %R",
                      tp->tp_name, name);
 
         _PyObject_SetAttributeErrorContext(obj, name);
@@ -2070,13 +2070,13 @@ _PyObject_GenericSetAttrWithDict(PyObject *obj, PyObject *name,
             if (descr == NULL) {
                 if (tp->tp_setattro == PyObject_GenericSetAttr) {
                     PyErr_Format(PyExc_AttributeError,
-                                "'%.100s' object has no attribute '%U' and no "
+                                "'%s' object has no attribute %R and no "
                                 "__dict__ for setting new attributes",
                                 tp->tp_name, name);
                 }
                 else {
                     PyErr_Format(PyExc_AttributeError,
-                                "'%.100s' object has no attribute '%U'",
+                                "'%s' object has no attribute %R",
                                 tp->tp_name, name);
                 }
                 _PyObject_SetAttributeErrorContext(obj, name);
@@ -2103,7 +2103,7 @@ _PyObject_GenericSetAttrWithDict(PyObject *obj, PyObject *name,
   error_check:
     if (res < 0 && PyErr_ExceptionMatches(PyExc_KeyError)) {
         PyErr_Format(PyExc_AttributeError,
-                        "'%.100s' object has no attribute '%U'",
+                        "'%s' object has no attribute %R",
                         tp->tp_name, name);
         _PyObject_SetAttributeErrorContext(obj, name);
     }

Objects/typeobject.c

@@ -6513,7 +6513,7 @@ _Py_type_getattro_stackref(PyTypeObject *type, PyObject *name,
     /* Give up */
     if (suppress_missing_attribute == NULL) {
         PyErr_Format(PyExc_AttributeError,
-                     "type object '%.100s' has no attribute '%U'",
+                     "type object '%s' has no attribute %R",
                      type->tp_name, name);
     }
     else {
@@ -6552,7 +6552,7 @@ type_update_dict(PyTypeObject *type, PyDictObject *dict, PyObject *name,
 
     if (_PyDict_SetItem_LockHeld(dict, name, value) < 0) {
         PyErr_Format(PyExc_AttributeError,
-                     "type object '%.50s' has no attribute '%U'",
+                     "type object '%s' has no attribute %R",
                      ((PyTypeObject*)type)->tp_name, name);
         _PyObject_SetAttributeErrorContext((PyObject *)type, name);
         return -1;