bpo-39320: Handle unpacking of *values in compiler (GH-17984)

* Add three new bytecodes: LIST_TO_TUPLE, LIST_EXTEND, SET_UPDATE. Use them to implement star unpacking expressions.

* Remove four bytecodes BUILD_LIST_UNPACK, BUILD_TUPLE_UNPACK, BUILD_SET_UNPACK and  BUILD_TUPLE_UNPACK_WITH_CALL opcodes as they are now unused.

* Update magic number and dis.rst for new bytecodes.

1 files changed, 34 insertions, 53 deletions

diff --git a/Python/ceval.c b/Python/ceval.c
index 5e586589e9..528ad7fdd1 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -2621,46 +2621,46 @@ main_loop:
             DISPATCH();
         }
 
-        case TARGET(BUILD_TUPLE_UNPACK_WITH_CALL):
-        case TARGET(BUILD_TUPLE_UNPACK):
-        case TARGET(BUILD_LIST_UNPACK): {
-            int convert_to_tuple = opcode != BUILD_LIST_UNPACK;
-            Py_ssize_t i;
-            PyObject *sum = PyList_New(0);
-            PyObject *return_value;
-
-            if (sum == NULL)
+        case TARGET(LIST_TO_TUPLE): {
+            PyObject *list = POP();
+            PyObject *tuple = PyList_AsTuple(list);
+            Py_DECREF(list);
+            if (tuple == NULL) {
                 goto error;
+            }
+            PUSH(tuple);
+            DISPATCH();
+        }
 
-            for (i = oparg; i > 0; i--) {
-                PyObject *none_val;
-
-                none_val = _PyList_Extend((PyListObject *)sum, PEEK(i));
-                if (none_val == NULL) {
-                    if (opcode == BUILD_TUPLE_UNPACK_WITH_CALL &&
-                        _PyErr_ExceptionMatches(tstate, PyExc_TypeError))
-                    {
-                        check_args_iterable(tstate, PEEK(1 + oparg), PEEK(i));
-                    }
-                    Py_DECREF(sum);
-                    goto error;
+        case TARGET(LIST_EXTEND): {
+            PyObject *iterable = POP();
+            PyObject *list = PEEK(oparg);
+            PyObject *none_val = _PyList_Extend((PyListObject *)list, iterable);
+            if (none_val == NULL) {
+                if (_PyErr_ExceptionMatches(tstate, PyExc_TypeError) &&
+                   (iterable->ob_type->tp_iter == NULL && !PySequence_Check(iterable)))
+                {
+                    PyErr_Clear();
+                    _PyErr_Format(tstate, PyExc_TypeError,
+                          "Value after * must be an iterable, not %.200s",
+                          Py_TYPE(iterable)->tp_name);
                 }
-                Py_DECREF(none_val);
+                Py_DECREF(iterable);
+                goto error;
             }
+            Py_DECREF(none_val);
+            Py_DECREF(iterable);
+            DISPATCH();
+        }
 
-            if (convert_to_tuple) {
-                return_value = PyList_AsTuple(sum);
-                Py_DECREF(sum);
-                if (return_value == NULL)
-                    goto error;
-            }
-            else {
-                return_value = sum;
+        case TARGET(SET_UPDATE): {
+            PyObject *iterable = POP();
+            PyObject *set = PEEK(oparg);
+            int err = _PySet_Update(set, iterable);
+            Py_DECREF(iterable);
+            if (err < 0) {
+                goto error;
             }
-
-            while (oparg--)
-                Py_DECREF(POP());
-            PUSH(return_value);
             DISPATCH();
         }
 
@@ -2685,25 +2685,6 @@ main_loop:
             DISPATCH();
         }
 
-        case TARGET(BUILD_SET_UNPACK): {
-            Py_ssize_t i;
-            PyObject *sum = PySet_New(NULL);
-            if (sum == NULL)
-                goto error;
-
-            for (i = oparg; i > 0; i--) {
-                if (_PySet_Update(sum, PEEK(i)) < 0) {
-                    Py_DECREF(sum);
-                    goto error;
-                }
-            }
-
-            while (oparg--)
-                Py_DECREF(POP());
-            PUSH(sum);
-            DISPATCH();
-        }
-
         case TARGET(BUILD_MAP): {
             Py_ssize_t i;
             PyObject *map = _PyDict_NewPresized((Py_ssize_t)oparg);