Issue #12946: Document that PyModule_GetDict can fail in some cases
diff --git a/Doc/c-api/module.rst b/Doc/c-api/module.rst
index 34f8443..e810c69 100644
--- a/Doc/c-api/module.rst
+++ b/Doc/c-api/module.rst
@@ -59,10 +59,13 @@
.. index:: single: __dict__ (module attribute)
Return the dictionary object that implements *module*'s namespace; this object
- is the same as the :attr:`~object.__dict__` attribute of the module object. This
- function never fails. It is recommended extensions use other
- :c:func:`PyModule_\*` and :c:func:`PyObject_\*` functions rather than directly
- manipulate a module's :attr:`~object.__dict__`.
+ is the same as the :attr:`~object.__dict__` attribute of the module object.
+ If *module* is not a module object (or a subtype of a module object),
+ :exc:`SystemError` is raised and *NULL* is returned.
+
+ It is recommended extensions use other :c:func:`PyModule_\*` and
+ :c:func:`PyObject_\*` functions rather than directly manipulate a module's
+ :attr:`~object.__dict__`.
.. c:function:: PyObject* PyModule_GetNameObject(PyObject *module)