gh-62912: return correct exception in python versions for operator.concat/iconcat

Author: skirpichev

Lib/operator.py

@@ -153,7 +153,7 @@ def xor(a, b):
 
 def concat(a, b):
     "Same as a + b, for a and b sequences."
-    if not hasattr(a, '__getitem__'):
+    if not hasattr(type(a), '__getitem__'):
         msg = "'%s' object can't be concatenated" % type(a).__name__
         raise TypeError(msg)
     return a + b
@@ -356,7 +356,7 @@ def iand(a, b):
 
 def iconcat(a, b):
     "Same as a += b, for a and b sequences."
-    if not hasattr(a, '__getitem__'):
+    if not hasattr(type(a), '__getitem__'):
         msg = "'%s' object can't be concatenated" % type(a).__name__
         raise TypeError(msg)
     a += b

Lib/test/test_operator.py

@@ -160,6 +160,12 @@ def test_concat(self):
         self.assertEqual(operator.concat(Seq1([5, 6]), Seq1([7])), [5, 6, 7])
         self.assertEqual(operator.concat(Seq2([5, 6]), Seq2([7])), [5, 6, 7])
         self.assertRaises(TypeError, operator.concat, 13, 29)
+        class A:
+            pass
+        a = A()
+        a.__getitem__ = lambda: "spam"
+        self.assertRaisesRegex(TypeError, "object can't be concatenated",
+                               operator.concat, a, a)
 
     def test_countOf(self):
         operator = self.module
@@ -551,6 +557,13 @@ def test_iconcat_without_getitem(self):
         with self.assertRaisesRegex(TypeError, msg):
             operator.iconcat(1, 0.5)
 
+        class A:
+            pass
+        a = A()
+        a.__getitem__ = lambda: "spam"
+        self.assertRaisesRegex(TypeError, "object can't be concatenated",
+                               operator.iconcat, a, a)
+
     def test_index(self):
         operator = self.module
         class X:

Misc/NEWS.d/next/Library/2026-04-03-04-17-59.gh-issue-62912.T6jQf5.rst

@@ -0,0 +1,3 @@
+Fix :func:`operator.concat` and :func:`operator.iconcat` to return a correct
+exception message, if the object class lacks the :meth:`~object.__getitem__`
+dunder.  Patch by Sergey B Kirpichev.