gh-142781: refactoring error message and deduplicating checks

Author: superboy-zjc

Lib/test/test_zoneinfo/test_zoneinfo.py

@@ -1588,9 +1588,12 @@ class ZI(self.klass):
         # to override zoneinfo.Zoneinfo.__init_subclass__.
         ZI._weak_cache = Cache()
 
-        with self.assertRaises(TypeError) as te:
+        with self.assertRaises(RuntimeError) as te:
             ZI("America/Los_Angeles")
-        self.assertEqual(str(te.exception), "expected ZI, got int")
+        self.assertEqual(
+            str(te.exception),
+            "Unexpected instance of int in ZI weak cache for key 'America/Los_Angeles'"
+        )
 
     def test_inconsistent_weak_cache_setdefault(self):
         class Cache:
@@ -1605,9 +1608,13 @@ class ZI(self.klass):
         # to override zoneinfo.Zoneinfo.__init_subclass__.
         ZI._weak_cache = Cache()
 
-        with self.assertRaises(TypeError) as te:
+        with self.assertRaises(RuntimeError) as te:
             ZI("America/Los_Angeles")
-        self.assertEqual(str(te.exception), "expected ZI, got int")
+        self.assertEqual(
+            str(te.exception),
+            "Unexpected instance of int in ZI weak cache for key 'America/Los_Angeles'"
+        )
+
 
 class ZoneInfoPickleTest(TzPathUserMixin, ZoneInfoTestBase):
     module = py_zoneinfo

Modules/_zoneinfo.c

@@ -335,27 +335,20 @@ zoneinfo_ZoneInfo_impl(PyTypeObject *type, PyObject *key)
             return NULL;
         }
 
+        ((PyZoneInfo_ZoneInfo *)tmp)->source = SOURCE_CACHE;
         instance =
             PyObject_CallMethod(weak_cache, "setdefault", "OO", key, tmp);
         Py_DECREF(tmp);
         if (instance == NULL) {
             Py_DECREF(weak_cache);
             return NULL;
         }
-
-        if (!PyObject_TypeCheck(instance, type)) {
-            PyErr_Format(PyExc_TypeError, "expected %s, got %s",
-                         type->tp_name, Py_TYPE(instance)->tp_name);
-            Py_DECREF(instance);
-            Py_DECREF(weak_cache);
-            return NULL;
-        }
-
-        ((PyZoneInfo_ZoneInfo *)instance)->source = SOURCE_CACHE;
     }
-    else if (!PyObject_TypeCheck(instance, type)) {
-        PyErr_Format(PyExc_TypeError, "expected %s, got %s",
-                     type->tp_name, Py_TYPE(instance)->tp_name);
+
+    if (!PyObject_TypeCheck(instance, type)) {
+        PyErr_Format(PyExc_RuntimeError,
+                     "Unexpected instance of %T in %s weak cache for key %R",
+                     instance, type->tp_name, key);
         Py_DECREF(instance);
         Py_DECREF(weak_cache);
         return NULL;