gh-132825: Enhance unhashable error messages for dict and set (#132828)

Lib/test/test_set.py

@@ -1,16 +1,17 @@
+import collections.abc
+import copy
+import gc
+import itertools
+import operator
+import pickle
+import re
 import unittest
+import warnings
+import weakref
+from random import randrange, shuffle
 from test import support
 from test.support import warnings_helper
-import gc
-import weakref
-import operator
-import copy
-import pickle
-from random import randrange, shuffle
-import warnings
-import collections
-import collections.abc
-import itertools
+
 
 class PassThru(Exception):
     pass
@@ -645,6 +646,35 @@ class TestSet(TestJointOps, unittest.TestCase):
         self.assertRaises(KeyError, myset.remove, set(range(1)))
         self.assertRaises(KeyError, myset.remove, set(range(3)))
 
+    def test_unhashable_element(self):
+        myset = {'a'}
+        elem = [1, 2, 3]
+
+        def check_unhashable_element():
+            msg = "cannot use 'list' as a set element (unhashable type: 'list')"
+            return self.assertRaisesRegex(TypeError, re.escape(msg))
+
+        with check_unhashable_element():
+            elem in myset
+        with check_unhashable_element():
+            myset.add(elem)
+        with check_unhashable_element():
+            myset.discard(elem)
+
+        # Only TypeError exception is overriden,
+        # other exceptions are left unchanged.
+        class HashError:
+            def __hash__(self):
+                raise KeyError('error')
+
+        elem2 = HashError()
+        with self.assertRaises(KeyError):
+            elem2 in myset
+        with self.assertRaises(KeyError):
+            myset.add(elem2)
+        with self.assertRaises(KeyError):
+            myset.discard(elem2)
+
 
 class SetSubclass(set):
     pass