Apply suggestions from code review

Co-authored-by: Victor Stinner <vstinner@python.org>

Author: encukou

Doc/c-api/gcsupport.rst

@@ -288,7 +288,10 @@ The :c:member:`~PyTypeObject.tp_traverse` handler must have the following type:
    :c:member:`~PyTypeObject.tp_flags` field, the traverse function must call
    :c:func:`PyObject_VisitManagedDict` like this::
 
-       PyObject_VisitManagedDict((PyObject*)self, visit, arg);
+       int err = PyObject_VisitManagedDict((PyObject*)self, visit, arg);
+       if (err) {
+           return err;
+       }
 
    Only the members that the instance *owns* (by having
    :term:`strong references <strong reference>` to them) must be
@@ -382,14 +385,14 @@ The following functions and macros are safe to use in a
 "DuringGC" functions
 ^^^^^^^^^^^^^^^^^^^^
 
-The following functions should *only* used in a
+The following functions should *only* be used in a
 :c:member:`~PyTypeObject.tp_traverse` handler; calling them in other
 contexts may have unintended consequences.
 
 These functions act like their counterparts without the ``_DuringGC`` suffix,
 but they are guaranteed to not have side effects, they do not set an exception
 on failure, and they return/set :term:`borrowed references <borrowed reference>`
-as detailed in the individual documentation..
+as detailed in the individual documentation.
 
 Note that these functions may fail (return ``NULL`` or ``-1``),
 but as they do not set an exception, no error information is available.

Modules/_testcapi/heaptype.c

@@ -537,7 +537,7 @@ static PyObject *
 pytype_getmodulebydef(PyObject *self, PyObject *type)
 {
     PyObject *mod = PyType_GetModuleByDef((PyTypeObject *)type, _testcapimodule);
-    assert(mod == PyType_GetModuleByDef((PyTypeObject *)type, _testcapimodule));
+    assert(mod == PyType_GetModuleByDef_DuringGC((PyTypeObject *)type, _testcapimodule));
     return Py_XNewRef(mod);
 }
 

Objects/typeobject.c

@@ -5745,9 +5745,6 @@ PyType_GetModule_DuringGC(PyTypeObject *type)
         return NULL;
     }
     PyHeapTypeObject* et = (PyHeapTypeObject*)type;
-    if (!et->ht_module) {
-        return NULL;
-    }
     return et->ht_module;
 }