Apply suggestions from code review

Co-authored-by: T. Wouters <thomas@python.org>

Author: carljm

Doc/c-api/function.rst

@@ -177,7 +177,8 @@ There are a few functions specific to Python functions.
    exception set on entry to the callback; in this case, the callback may not
    execute Python code or otherwise disturb the pending exception. Taking a
    reference in the callback to an about-to-be-destroyed function will resurrect
-   it and prevent it from being freed.
+   it, preventing it from being freed at this time. When the resurrected object is destroyed later,
+   any watcher callbacks active at the time will be called again.
 
    If the callback sets an exception, it must return ``-1``; this exception will
    be printed as an unraisable exception using :c:func:`PyErr_WriteUnraisable`.

Objects/codeobject.c

@@ -37,8 +37,7 @@ notify_code_watchers(PyCodeEvent event, PyCodeObject *co)
                     Py_DECREF(repr);
                 }
                 if (context == NULL) {
-                    context = Py_None;
-                    Py_INCREF(context);
+                    context = Py_NewRef(Py_None);
                 }
                 PyErr_WriteUnraisable(context);
                 Py_DECREF(context);

Objects/dictobject.c

@@ -2311,7 +2311,7 @@ dict_dealloc(PyDictObject *mp)
     assert(Py_REFCNT(mp) == 0);
     Py_SET_REFCNT(mp, 1);
     _PyDict_NotifyEvent(PyDict_EVENT_DEALLOCATED, mp, NULL, NULL);
-    if(Py_REFCNT(mp) > 1) {
+    if (Py_REFCNT(mp) > 1) {
         Py_DECREF(mp);
         return;
     }
@@ -5757,8 +5757,7 @@ _PyDict_SendEvent(int watcher_bits,
                 // repr can call arbitrary code, so we invent a simpler version.
                 PyObject *context = PyUnicode_FromFormat("watcher callback for <dict at %p>", mp);
                 if (context == NULL) {
-                    context = Py_None;
-                    Py_INCREF(context);
+                    context = Py_NewRef(Py_None);
                 }
                 PyErr_WriteUnraisable(context);
                 Py_DECREF(context);

Objects/funcobject.c

@@ -32,8 +32,7 @@ notify_func_watchers(PyInterpreterState *interp, PyFunction_WatchEvent event,
                     Py_DECREF(repr);
                 }
                 if (context == NULL) {
-                    context = Py_None;
-                    Py_INCREF(context);
+                    context = Py_NewRef(Py_None);
                 }
                 PyErr_WriteUnraisable(context);
                 Py_DECREF(context);