bpo-36370: Check for PyErr_Occurred() after PyImport_GetModule() (GH-12504)

Python/ceval.c

@@ -4948,7 +4948,7 @@ import_from(PyObject *v, PyObject *name)
     }
     x = PyImport_GetModule(fullmodname);
     Py_DECREF(fullmodname);
-    if (x == NULL) {
+    if (x == NULL && !PyErr_Occurred()) {
         goto error;
     }
     Py_DECREF(pkgname);
@@ -4971,7 +4971,7 @@ import_from(PyObject *v, PyObject *name)
             "cannot import name %R from %R (unknown location)",
             name, pkgname_or_unknown
         );
-        /* NULL check for errmsg done by PyErr_SetImportError. */
+        /* NULL checks for errmsg and pkgname done by PyErr_SetImportError. */
         PyErr_SetImportError(errmsg, pkgname, NULL);
     }
     else {
@@ -4979,7 +4979,7 @@ import_from(PyObject *v, PyObject *name)
             "cannot import name %R from %R (%S)",
             name, pkgname_or_unknown, pkgpath
         );
-        /* NULL check for errmsg done by PyErr_SetImportError. */
+        /* NULL checks for errmsg and pkgname done by PyErr_SetImportError. */
         PyErr_SetImportError(errmsg, pkgname, pkgpath);
     }
 

Python/import.c

@@ -966,11 +966,10 @@ exec_code_in_module(PyObject *name, PyObject *module_dict, PyObject *code_object
     Py_DECREF(v);
 
     m = PyImport_GetModule(name);
-    if (m == NULL) {
+    if (m == NULL && !PyErr_Occurred()) {
         PyErr_Format(PyExc_ImportError,
                      "Loaded module %R not found in sys.modules",
                      name);
-        return NULL;
     }
 
     return m;
@@ -1735,6 +1734,10 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *globals,
     }
 
     mod = PyImport_GetModule(abs_name);
+    if (mod == NULL && PyErr_Occurred()) {
+        goto error;
+    }
+
     if (mod != NULL && mod != Py_None) {
         _Py_IDENTIFIER(__spec__);
         _Py_IDENTIFIER(_lock_unlock_module);
@@ -1810,9 +1813,11 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *globals,
                 final_mod = PyImport_GetModule(to_return);
                 Py_DECREF(to_return);
                 if (final_mod == NULL) {
-                    PyErr_Format(PyExc_KeyError,
+                    if (!PyErr_Occurred()) {
-                                 "%R not in sys.modules as expected",
+                        PyErr_Format(PyExc_KeyError,
-                                 to_return);
+                                     "%R not in sys.modules as expected",
+                                     to_return);
+                    }
                     goto error;
                 }
             }
@@ -1875,6 +1880,10 @@ PyImport_ReloadModule(PyObject *m)
     PyObject *reloaded_module = NULL;
     PyObject *imp = _PyImport_GetModuleId(&PyId_imp);
     if (imp == NULL) {
+        if (PyErr_Occurred()) {
+            return NULL;
+        }
+
         imp = PyImport_ImportModule("imp");
         if (imp == NULL) {
             return NULL;

Python/pylifecycle.c

@@ -2157,8 +2157,10 @@ wait_for_thread_shutdown(void)
     PyObject *result;
     PyObject *threading = _PyImport_GetModuleId(&PyId_threading);
     if (threading == NULL) {
-        /* threading not imported */
+        if (PyErr_Occurred()) {
-        PyErr_Clear();
+            PyErr_WriteUnraisable(NULL);
+        }
+        /* else: threading not imported */
         return;
     }
     result = _PyObject_CallMethodId(threading, &PyId__shutdown, NULL);

Python/sysmodule.c

@@ -283,7 +283,9 @@ sys_displayhook(PyObject *module, PyObject *o)
 
     builtins = _PyImport_GetModuleId(&PyId_builtins);
     if (builtins == NULL) {
-        PyErr_SetString(PyExc_RuntimeError, "lost builtins module");
+        if (!PyErr_Occurred()) {
+            PyErr_SetString(PyExc_RuntimeError, "lost builtins module");
+        }
         return NULL;
     }
     Py_DECREF(builtins);