Issue #16991: Add a C implementation of collections.OrderedDict.
diff --git a/Include/odictobject.h b/Include/odictobject.h
new file mode 100644
index 0000000..a32fbc5
--- /dev/null
+++ b/Include/odictobject.h
@@ -0,0 +1,42 @@
+#ifndef Py_ODICTOBJECT_H
+#define Py_ODICTOBJECT_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+/* OrderedDict */
+
+#ifndef Py_LIMITED_API
+
+typedef struct _odictobject PyODictObject;
+
+PyAPI_DATA(PyTypeObject) PyODict_Type;
+PyAPI_DATA(PyTypeObject) PyODictIter_Type;
+PyAPI_DATA(PyTypeObject) PyODictKeys_Type;
+PyAPI_DATA(PyTypeObject) PyODictItems_Type;
+PyAPI_DATA(PyTypeObject) PyODictValues_Type;
+
+#endif /* Py_LIMITED_API */
+
+#define PyODict_Check(op) PyObject_IsInstance(op, (PyObject *)&PyODict_Type)
+#define PyODict_CheckExact(op) (Py_TYPE(op) == &PyODict_Type)
+#define PyODict_SIZE(op) ((PyDictObject *)op)->ma_used
+#define PyODict_HasKey(od, key) (PyMapping_HasKey(PyObject *)od, key)
+
+PyAPI_FUNC(PyObject *) PyODict_New(void);
+PyAPI_FUNC(int) PyODict_SetItem(PyObject *od, PyObject *key, PyObject *item);
+PyAPI_FUNC(int) PyODict_DelItem(PyObject *od, PyObject *key);
+
+/* wrappers around PyDict* functions */
+#define PyODict_GetItem(od, key) PyDict_GetItem((PyObject *)od, key)
+#define PyODict_Contains(od, key) PyDict_Contains((PyObject *)od, key)
+#define PyODict_Size(od) PyDict_Size((PyObject *)od)
+#define PyODict_GetItemString(od, key) \
+ PyDict_GetItemString((PyObject *)od, key)
+#define Py_ODict_GetItemId(od, key) _PyDict_GetItemId((PyObject *)od, key)
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* !Py_ODICTOBJECT_H */