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Add warning for scope of exec #47

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6af2ec3
add warning for scope issue of exec
Apr 7, 2026
47cfb82
fix bugs
Apr 16, 2026
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20 changes: 20 additions & 0 deletions Lib/test/test_py3kwarn.py
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
import unittest
import sys
from test.test_support import check_py3k_warnings, CleanImport, run_unittest
from test.script_helper import assert_python_ok
import warnings
import base64
from test import test_support
Expand Down Expand Up @@ -430,6 +431,25 @@ def test_b16encode_warns(self):
base64.b16encode(b'test')
check_py3k_warnings(expected, UserWarning)

def assertExecLocalWritebackWarning(self, recorder, local_name):
self.assertEqual(len(recorder.warnings), 1)
msg = str(recorder.warnings[0].message)
self.assertTrue(msg.startswith(
"exec() modified local '%s'" % local_name))
recorder.reset()

def test_exec_local_writeback_warning(self):
rc, out, err = assert_python_ok(
"-3",
"-c",
"def f(code):\n"
" b = 42\n"
" exec code\n"
" return b\n"
"f('b = 99')\n")
self.assertEqual(rc, 0)
self.assertIn("exec() modified local 'b' which is read later", err)


class TestStdlibRemovals(unittest.TestCase):

Expand Down
269 changes: 269 additions & 0 deletions Python/ceval.c
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Original file line number Diff line number Diff line change
Expand Up @@ -66,6 +66,175 @@ _Py3kWarn_NextOpcode(void)
return -1;
}

static PyObject *exec_local_writeback_map = NULL;

static PyObject *
_get_exec_local_writeback_map(void)
{
if (exec_local_writeback_map == NULL) {
exec_local_writeback_map = PyDict_New();
}
return exec_local_writeback_map;
}

static void
_clear_exec_local_writeback_for_frame(PyFrameObject *f)
{
PyObject *frame_key;
PyObject *exc_type, *exc_value, *exc_tb;

if (exec_local_writeback_map == NULL) {
return;
}
PyErr_Fetch(&exc_type, &exc_value, &exc_tb);
frame_key = PyLong_FromVoidPtr(f);
if (frame_key == NULL) {
PyErr_Clear();
PyErr_Restore(exc_type, exc_value, exc_tb);
return;
}
if (PyDict_GetItem(exec_local_writeback_map, frame_key) != NULL) {
if (PyDict_DelItem(exec_local_writeback_map, frame_key) < 0) {
PyErr_Clear();
}
}
Py_DECREF(frame_key);
PyErr_Restore(exc_type, exc_value, exc_tb);
}

static int
_warn_exec_local_writeback(PyFrameObject *f, int oparg)
{
PyObject *frame_key = NULL;
PyObject *frame_dict = NULL;
PyObject *entry = NULL;
PyObject *idx = NULL;
PyObject *msg = NULL;
PyObject *name_obj = NULL;
const char *local_name = NULL;
int read_lineno = 0;
int warn_result;

if (exec_local_writeback_map == NULL) {
return 0;
}
frame_key = PyLong_FromVoidPtr(f);
if (frame_key == NULL) {
PyErr_Clear();
return 0;
}
frame_dict = PyDict_GetItem(exec_local_writeback_map, frame_key);
if (frame_dict == NULL) {
Py_DECREF(frame_key);
return 0;
}
idx = PyInt_FromLong(oparg);
if (idx == NULL) {
Py_DECREF(frame_key);
PyErr_Clear();
return 0;
}
entry = PyDict_GetItem(frame_dict, idx);
if (entry == NULL) {
Py_DECREF(idx);
Py_DECREF(frame_key);
return 0;
}
read_lineno = PyCode_Addr2Line(f->f_code, f->f_lasti);
name_obj = PyTuple_GetItem(f->f_code->co_varnames, oparg);
if (name_obj != NULL) {
local_name = PyString_AsString(name_obj);
}
if (local_name == NULL) {
local_name = "<local>";
}
msg = PyString_FromFormat(
"exec() modified local '%s' which is read later in the enclosing function; "
"in 3.x exec() does not reliably write back to function locals without an explicit locals mapping",
local_name);
if (msg == NULL) {
Py_DECREF(idx);
Py_DECREF(frame_key);
PyErr_Clear();
return 0;
}

warn_result = PyErr_WarnExplicit_WithFix(
PyExc_Py3xWarning,
PyString_AsString(msg),
"use exec(code, globals, locals) with an explicit locals mapping",
PyString_AsString(f->f_code->co_filename),
read_lineno,
NULL,
NULL);

Py_DECREF(msg);
if (warn_result < 0) {
Py_DECREF(idx);
Py_DECREF(frame_key);
return -1;
}

if (PyDict_DelItem(frame_dict, idx) < 0) {
PyErr_Clear();
}
Py_DECREF(idx);

if (PyDict_Size(frame_dict) <= 0) {
if (PyDict_DelItem(exec_local_writeback_map, frame_key) < 0) {
PyErr_Clear();
}
}
Py_DECREF(frame_key);
return 0;
}

static void
_clear_exec_local_writeback_for_local(PyFrameObject *f, int oparg)
{
PyObject *frame_key = NULL;
PyObject *frame_dict = NULL;
PyObject *idx = NULL;
PyObject *exc_type, *exc_value, *exc_tb;

if (exec_local_writeback_map == NULL) {
return;
}
PyErr_Fetch(&exc_type, &exc_value, &exc_tb);
frame_key = PyLong_FromVoidPtr(f);
if (frame_key == NULL) {
PyErr_Clear();
PyErr_Restore(exc_type, exc_value, exc_tb);
return;
}
frame_dict = PyDict_GetItem(exec_local_writeback_map, frame_key);
if (frame_dict == NULL) {
Py_DECREF(frame_key);
PyErr_Restore(exc_type, exc_value, exc_tb);
return;
}
idx = PyInt_FromLong(oparg);
if (idx == NULL) {
Py_DECREF(frame_key);
PyErr_Clear();
PyErr_Restore(exc_type, exc_value, exc_tb);
return;
}
if (PyDict_GetItem(frame_dict, idx) != NULL) {
if (PyDict_DelItem(frame_dict, idx) < 0) {
PyErr_Clear();
}
}
Py_DECREF(idx);
if (PyDict_Size(frame_dict) <= 0) {
if (PyDict_DelItem(exec_local_writeback_map, frame_key) < 0) {
PyErr_Clear();
}
}
Py_DECREF(frame_key);
PyErr_Restore(exc_type, exc_value, exc_tb);
}

#ifndef WITH_TSC

#define READ_TIMESTAMP(var)
Expand Down Expand Up @@ -1273,6 +1442,12 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
{
x = GETLOCAL(oparg);
if (x != NULL) {
if (Py_Py3kWarningFlag) {
if (_warn_exec_local_writeback(f, oparg) < 0) {
err = -1;
break;
}
}
Py_INCREF(x);
PUSH(x);
FAST_DISPATCH();
Expand All @@ -1296,6 +1471,9 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
{
v = POP();
SETLOCAL(oparg, v);
if (Py_Py3kWarningFlag) {
_clear_exec_local_writeback_for_local(f, oparg);
}
FAST_DISPATCH();
}

Expand Down Expand Up @@ -2454,6 +2632,9 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
x = GETLOCAL(oparg);
if (x != NULL) {
SETLOCAL(oparg, NULL);
if (Py_Py3kWarningFlag) {
_clear_exec_local_writeback_for_local(f, oparg);
}
DISPATCH();
}
format_exc_check_arg(
Expand Down Expand Up @@ -3404,6 +3585,7 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)

/* pop frame */
exit_eval_frame:
_clear_exec_local_writeback_for_frame(f);
Py_LeaveRecursiveCall();
tstate->frame = f->f_back;

Expand Down Expand Up @@ -5086,6 +5268,12 @@ exec_statement(PyFrameObject *f, PyObject *prog, PyObject *globals,
int n;
PyObject *v;
int plain = 0;
int track_locals = 0;
int exec_lineno = 0;
int exec_offset = 0;
int nlocals = 0;
PyObject **before = NULL;
int i;

if (PyTuple_Check(prog) && globals == Py_None && locals == Py_None &&
((n = PyTuple_Size(prog)) == 2 || n == 3)) {
Expand Down Expand Up @@ -5131,6 +5319,23 @@ exec_statement(PyFrameObject *f, PyObject *prog, PyObject *globals,
}
if (PyDict_GetItemString(globals, "__builtins__") == NULL)
PyDict_SetItemString(globals, "__builtins__", f->f_builtins);

if (plain && Py_Py3kWarningFlag &&
(f->f_code->co_flags & CO_NEWLOCALS) &&
f->f_code->co_nlocals > 0 &&
f->f_localsplus != NULL) {
nlocals = f->f_code->co_nlocals;
before = PyMem_New(PyObject *, nlocals);
if (before != NULL) {
for (i = 0; i < nlocals; i++) {
before[i] = f->f_localsplus[i];
Py_XINCREF(before[i]);
}
track_locals = 1;
exec_offset = f->f_lasti;
exec_lineno = PyCode_Addr2Line(f->f_code, exec_offset);
}
}
if (PyCode_Check(prog)) {
if (PyCode_GetNumFree((PyCodeObject *)prog) > 0) {
PyErr_SetString(PyExc_TypeError,
Expand Down Expand Up @@ -5178,6 +5383,70 @@ exec_statement(PyFrameObject *f, PyObject *prog, PyObject *globals,
}
if (plain)
PyFrame_LocalsToFast(f, 0);
if (track_locals && v != NULL) {
PyObject *frame_key = NULL;
PyObject *frame_dict = NULL;
PyObject *map = NULL;
for (i = 0; i < nlocals; i++) {
PyObject *before_obj = before[i];
PyObject *after_obj = f->f_localsplus[i];
if (before_obj == after_obj) {
continue;
}
if (frame_key == NULL) {
frame_key = PyLong_FromVoidPtr(f);
if (frame_key == NULL) {
PyErr_Clear();
break;
}
}
if (map == NULL) {
map = _get_exec_local_writeback_map();
if (map == NULL) {
PyErr_Clear();
break;
}
}
if (frame_dict == NULL) {
frame_dict = PyDict_GetItem(map, frame_key);
if (frame_dict == NULL) {
frame_dict = PyDict_New();
if (frame_dict == NULL) {
PyErr_Clear();
break;
}
if (PyDict_SetItem(map, frame_key, frame_dict) < 0) {
PyErr_Clear();
Py_DECREF(frame_dict);
frame_dict = NULL;
break;
}
Py_DECREF(frame_dict);
frame_dict = PyDict_GetItem(map, frame_key);
}
}
if (frame_dict != NULL) {
PyObject *idx = PyInt_FromLong(i);
PyObject *val = Py_BuildValue("ii", exec_lineno, exec_offset);
if (idx != NULL && val != NULL) {
if (PyDict_SetItem(frame_dict, idx, val) < 0) {
PyErr_Clear();
}
} else {
PyErr_Clear();
}
Py_XDECREF(idx);
Py_XDECREF(val);
}
}
Py_XDECREF(frame_key);
}
if (before != NULL) {
for (i = 0; i < nlocals; i++) {
Py_XDECREF(before[i]);
}
PyMem_Free(before);
}
if (v == NULL)
return -1;
Py_DECREF(v);
Expand Down