gh-112716: Fix SystemError when __builtins__ is not a dict (GH-112770)

It was raised in two cases:
* in the import statement when looking up __import__
* in pickling some builtin type when looking up built-ins iter, getattr, etc.

Author: serhiy-storchaka

Lib/test/test_builtin.py

@@ -837,6 +837,32 @@ class customdict(dict):  # this one should not do anything fancy
         self.assertRaisesRegex(NameError, "name 'superglobal' is not defined",
                                exec, code, {'__builtins__': customdict()})
 
+    def test_eval_builtins_mapping(self):
+        code = compile("superglobal", "test", "eval")
+        # works correctly
+        ns = {'__builtins__': types.MappingProxyType({'superglobal': 1})}
+        self.assertEqual(eval(code, ns), 1)
+        # custom builtins mapping is missing key
+        ns = {'__builtins__': types.MappingProxyType({})}
+        self.assertRaisesRegex(NameError, "name 'superglobal' is not defined",
+                               eval, code, ns)
+
+    def test_exec_builtins_mapping_import(self):
+        code = compile("import foo.bar", "test", "exec")
+        ns = {'__builtins__': types.MappingProxyType({})}
+        self.assertRaisesRegex(ImportError, "__import__ not found", exec, code, ns)
+        ns = {'__builtins__': types.MappingProxyType({'__import__': lambda *args: args})}
+        exec(code, ns)
+        self.assertEqual(ns['foo'], ('foo.bar', ns, ns, None, 0))
+
+    def test_eval_builtins_mapping_reduce(self):
+        # list_iterator.__reduce__() calls _PyEval_GetBuiltin("iter")
+        code = compile("x.__reduce__()", "test", "eval")
+        ns = {'__builtins__': types.MappingProxyType({}), 'x': iter([1, 2])}
+        self.assertRaisesRegex(AttributeError, "iter", eval, code, ns)
+        ns = {'__builtins__': types.MappingProxyType({'iter': iter}), 'x': iter([1, 2])}
+        self.assertEqual(eval(code, ns), (iter, ([1, 2],), 0))
+
     def test_exec_redirected(self):
         savestdout = sys.stdout
         sys.stdout = None # Whatever that cannot flush()

Misc/NEWS.d/next/Core and Builtins/2023-12-05-20-41-58.gh-issue-112716.hOcx0Y.rst

@@ -0,0 +1,2 @@
+Fix SystemError in the ``import`` statement and in ``__reduce__()`` methods
+of builtin types when ``__builtins__`` is not a dict.

Python/ceval.c

@@ -2417,7 +2417,7 @@ PyObject *
 _PyEval_GetBuiltin(PyObject *name)
 {
     PyObject *attr;
-    if (PyDict_GetItemRef(PyEval_GetBuiltins(), name, &attr) == 0) {
+    if (PyMapping_GetOptionalItem(PyEval_GetBuiltins(), name, &attr) == 0) {
         PyErr_SetObject(PyExc_AttributeError, name);
     }
     return attr;
@@ -2570,7 +2570,7 @@ import_name(PyThreadState *tstate, _PyInterpreterFrame *frame,
             PyObject *name, PyObject *fromlist, PyObject *level)
 {
     PyObject *import_func;
-    if (PyDict_GetItemRef(frame->f_builtins, &_Py_ID(__import__), &import_func) < 0) {
+    if (PyMapping_GetOptionalItem(frame->f_builtins, &_Py_ID(__import__), &import_func) < 0) {
         return NULL;
     }
     if (import_func == NULL) {