Fix incorrect AttributeError for invalid AnyValue types (#4821)

opentelemetry-api/src/opentelemetry/attributes/__init__.py

@@ -36,6 +36,13 @@
 )
 
 
+# TODO: Remove this workaround and revert to the simpler implementation
+# once Python 3.9 support is dropped (planned around May 2026).
+# This exists only to avoid issues caused by deprecated behavior in 3.9.
+def _type_name(t):
+    return getattr(t, "__name__", getattr(t, "_name", repr(t)))
+
+
 _logger = logging.getLogger(__name__)
 
 
@@ -190,7 +197,7 @@ def _clean_extended_attribute_value(  # pylint: disable=too-many-branches
     except Exception:
         raise TypeError(
             f"Invalid type {type(value).__name__} for attribute value. "
-            f"Expected one of {[valid_type.__name__ for valid_type in _VALID_ANY_VALUE_TYPES]} or a "
+            f"Expected one of {[_type_name(valid_type) for valid_type in _VALID_ANY_VALUE_TYPES]} or a "
             "sequence of those types",
         )
 

opentelemetry-api/tests/attributes/test_attributes.py

@@ -15,12 +15,14 @@
 # type: ignore
 
 import unittest
+import unittest.mock
 from typing import MutableSequence
 
 from opentelemetry.attributes import (
     BoundedAttributes,
     _clean_attribute,
     _clean_extended_attribute,
+    _clean_extended_attribute_value,
 )
 
 
@@ -320,3 +322,11 @@ def __str__(self):
         self.assertEqual(
             "<DummyWSGIRequest method=GET path=/example/>", cleaned_value
         )
+
+    def test_invalid_anyvalue_type_raises_typeerror(self):
+        class BadStr:
+            def __str__(self):
+                raise Exception("boom")
+
+        with self.assertRaises(TypeError):
+            _clean_extended_attribute_value(BadStr(), None)