Performance optimization for upb python extend repeated scalars.

Before:
_bench_append, 100000, 241.9
_bench_extend, 100000, 112.3
_bench_assign, 100000, 83.3
_bench_pybind11, 100000, 16.2

After:
_bench_append, 100000, 224.3
_bench_extend, 100000, 71.2
_bench_assign, 100000, 81.1
_bench_pybind11, 100000, 14.7
PiperOrigin-RevId: 707749522

python/google/protobuf/internal/message_test.py

@@ -1068,6 +1068,8 @@ def testExtendInt32WithPythonList(self, message_module):
     self.assertSequenceEqual([0, 1, 2], m.repeated_int32)
     m.repeated_int32.extend([3, 4])
     self.assertSequenceEqual([0, 1, 2, 3, 4], m.repeated_int32)
+    with self.assertRaises(TypeError):
+      m.repeated_int32.extend([5, 6, 'hi', 7])
 
   def testExtendFloatWithPythonList(self, message_module):
     """Test extending repeated float fields with python lists."""

python/repeated.c

@@ -181,15 +181,36 @@ PyObject* PyUpb_RepeatedContainer_Extend(PyObject* _self, PyObject* value) {
   bool submsg = upb_FieldDef_IsSubMessage(f);
   PyObject* e;
 
-  while ((e = PyIter_Next(it))) {
-    PyObject* ret;
-    if (submsg) {
-      ret = PyUpb_RepeatedCompositeContainer_Append(_self, e);
-    } else {
-      ret = PyUpb_RepeatedScalarContainer_Append(_self, e);
+  Py_ssize_t size = PyObject_Size(value);
+  if (size < 0) {
+    PyErr_Clear();
+  }
+  if ((size > 0) && (!submsg)) {
+    upb_Arena* arena = PyUpb_Arena_Get(self->arena);
+    const upb_FieldDef* f = PyUpb_RepeatedContainer_GetField(self);
+    upb_Array_Resize(arr, start_size + size, arena);
+    int index = start_size;
+    while ((e = PyIter_Next(it))) {
+      upb_MessageValue msgval;
+      if (!PyUpb_PyToUpb(e, f, &msgval, arena)) {
+        Py_DECREF(e);
+        break;
+      }
+      upb_Array_Set(arr, index, msgval);
+      Py_DECREF(e);
+      index++;
+    }
+  } else {
+    while ((e = PyIter_Next(it))) {
+      PyObject* ret;
+      if (submsg) {
+        ret = PyUpb_RepeatedCompositeContainer_Append(_self, e);
+      } else {
+        ret = PyUpb_RepeatedScalarContainer_Append(_self, e);
+      }
+      Py_XDECREF(ret);
+      Py_DECREF(e);
     }
-    Py_XDECREF(ret);
-    Py_DECREF(e);
   }
 
   Py_DECREF(it);