python · Wulian233 · Sep 12, 2026
diff --git a/Lib/test/test_opcache.py b/Lib/test/test_opcache.py
@@ -2094,6 +2094,18 @@ def for_iter_tuple():
         self.assert_specialized(for_iter_tuple, "FOR_ITER_TUPLE")
         self.assert_no_opcode(for_iter_tuple, "FOR_ITER")
 
+        b = b"\x00\x7f\x80\xff" * 3
+        result = []
+        def for_iter_bytes():
+            result.clear()
+            for i in b:
+                result.append(i)
+
+        for_iter_bytes()
+        self.assertEqual(result, list(b))
+        self.assert_specialized(for_iter_bytes, "FOR_ITER_VIRTUAL")
+        self.assert_no_opcode(for_iter_bytes, "FOR_ITER")
+
         s = "abcdefghij"
         def for_iter_str():
             for i in s:

diff --git a/...EWS.d/next/Core_and_Builtins/2026-09-12-12-14-00.gh-issue-132509.bytes-iter.rst b/...EWS.d/next/Core_and_Builtins/2026-09-12-12-14-00.gh-issue-132509.bytes-iter.rst
@@ -0,0 +1,2 @@
+Speed up iteration over exact :class:`bytes` objects by inlining item
+retrieval in the bytecode interpreter.
diff --git a/Modules/_testinternalcapi/test_cases.c.h b/Modules/_testinternalcapi/test_cases.c.h
@@ -3883,7 +3883,27 @@ dummy_func(
         replaced op(_FOR_ITER_VIRTUAL, (iter, null_or_index -- iter, null_or_index, next)) {
             PyObject *iter_o = PyStackRef_AsPyObjectBorrow(iter);
             Py_ssize_t index = PyStackRef_UntagInt(null_or_index);
-            _PyObjectIndexPair next_index = Py_TYPE(iter_o)->_tp_iteritem(iter_o, index);
+            _PyObjectIndexPair next_index;
+            if (PyBytes_CheckExact(iter_o)) {
+                if ((size_t)index >= (size_t)PyBytes_GET_SIZE(iter_o)) {
+                    next_index = (_PyObjectIndexPair) {
+                        .object = NULL,
+                        .index = index,
+                    };
+                }
+                else {
+                    unsigned char value = (unsigned char)
+                        ((PyBytesObject *)iter_o)->ob_sval[index];
+                    next_index = (_PyObjectIndexPair) {
+                        .object = (PyObject *)&_PyLong_SMALL_INTS[
+                            _PY_NSMALLNEGINTS + value],
+                        .index = index + 1,
+                    };
+                }
+            }
+            else {
+                next_index = Py_TYPE(iter_o)->_tp_iteritem(iter_o, index);
+            }
             PyObject *next_o = next_index.object;
             index = next_index.index;
             if (next_o == NULL) {

diff --git a/Python/generated_cases.c.h b/Python/generated_cases.c.h
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Speed up iteration over exact :class:`bytes` objects by inlining item
		retrieval in the bytecode interpreter.