bpo-26868: Fix example usage of PyModule_AddObject. (#15725)

* Add a note to the PyModule_AddObject docs.

* Correct example usages of PyModule_AddObject.

* Whitespace.

* Clean up wording.

* 📜🤖 Added by blurb_it.

* First code review.

* Add < 0 in the tests with PyModule_AddObject

2 files changed, 27 insertions, 7 deletions

diff --git a/Doc/extending/extending.rst b/Doc/extending/extending.rst
index e459514b2b..5b4ea8220e 100644
--- a/Doc/extending/extending.rst
+++ b/Doc/extending/extending.rst
@@ -209,7 +209,7 @@ usually declare a static object variable at the beginning of your file::
    static PyObject *SpamError;
 
 and initialize it in your module's initialization function (:c:func:`PyInit_spam`)
-with an exception object (leaving out the error checking for now)::
+with an exception object::
 
    PyMODINIT_FUNC
    PyInit_spam(void)
@@ -221,8 +221,14 @@ with an exception object (leaving out the error checking for now)::
            return NULL;
 
        SpamError = PyErr_NewException("spam.error", NULL, NULL);
-       Py_INCREF(SpamError);
-       PyModule_AddObject(m, "error", SpamError);
+       Py_XINCREF(SpamError);
+       if (PyModule_AddObject(m, "error", SpamError) < 0) {
+           Py_XDECREF(SpamError);
+           Py_CLEAR(SpamError);
+           Py_DECREF(m);
+           return NULL;
+       }
+
        return m;
    }
 
@@ -1261,8 +1267,12 @@ function must take care of initializing the C API pointer array::
        /* Create a Capsule containing the API pointer array's address */
        c_api_object = PyCapsule_New((void *)PySpam_API, "spam._C_API", NULL);
 
-       if (c_api_object != NULL)
-           PyModule_AddObject(m, "_C_API", c_api_object);
+       if (PyModule_AddObject(m, "_C_API", c_api_object) < 0) {
+           Py_XDECREF(c_api_object);
+           Py_DECREF(m);
+           return NULL;
+       }
+
        return m;
    }
 
diff --git a/Doc/extending/newtypes_tutorial.rst b/Doc/extending/newtypes_tutorial.rst
index 59c8cc0122..94ca747c7a 100644
--- a/Doc/extending/newtypes_tutorial.rst
+++ b/Doc/extending/newtypes_tutorial.rst
@@ -179,7 +179,12 @@ This initializes the :class:`Custom` type, filling in a number of members
 to the appropriate default values, including :attr:`ob_type` that we initially
 set to *NULL*. ::
 
-   PyModule_AddObject(m, "Custom", (PyObject *) &CustomType);
+   Py_INCREF(&CustomType);
+   if (PyModule_AddObject(m, "Custom", (PyObject *) &CustomType) < 0) {
+       Py_DECREF(&CustomType);
+       PY_DECREF(m);
+       return NULL;
+   }
 
 This adds the type to the module dictionary.  This allows us to create
 :class:`Custom` instances by calling the :class:`Custom` class:
@@ -864,7 +869,12 @@ function::
            return NULL;
 
        Py_INCREF(&SubListType);
-       PyModule_AddObject(m, "SubList", (PyObject *) &SubListType);
+       if (PyModule_AddObject(m, "SubList", (PyObject *) &SubListType) < 0) {
+           Py_DECREF(&SubListType);
+           Py_DECREF(m);
+           return NULL;
+       }
+
        return m;
    }