The weak reference implementation, separated from the weakref module.

Include/weakrefobject.h

+/* Weak references objects for Python. */
+
+#ifndef Py_WEAKREFOBJECT_H
+#define Py_WEAKREFOBJECT_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+typedef struct _PyWeakReference PyWeakReference;
+
+struct _PyWeakReference {
+    PyObject_HEAD
+    PyObject *wr_object;
+    PyObject *wr_callback;
+    long hash;
+    PyWeakReference *wr_prev;
+    PyWeakReference *wr_next;
+};
+
+extern DL_IMPORT(PyTypeObject) _PyWeakref_RefType;
+extern DL_IMPORT(PyTypeObject) _PyWeakref_ProxyType;
+extern DL_IMPORT(PyTypeObject) _PyWeakref_CallableProxyType;
+
+extern DL_IMPORT(PyObject *) PyErr_ReferenceError;
+
+#define PyWeakref_CheckRef(op) \
+        ((op)->ob_type == &_PyWeakref_RefType)
+#define PyWeakref_CheckProxy(op) \
+        (((op)->ob_type == &_PyWeakref_ProxyType) || \
+         ((op)->ob_type == &_PyWeakref_CallableProxyType))
+#define PyWeakref_Check(op) \
+        (PyWeakref_CheckRef(op) || PyWeakref_CheckProxy(op))
+
+
+extern DL_IMPORT(PyObject *) PyWeakref_NewRef(PyObject *ob,
+                                              PyObject *callback);
+extern DL_IMPORT(PyObject *) PyWeakref_NewProxy(PyObject *ob,
+                                                PyObject *callback);
+extern DL_IMPORT(PyObject *) PyWeakref_GetObject(PyObject *ref);
+
+extern DL_IMPORT(long) _PyWeakref_GetWeakrefCount(PyWeakReference *head);
+
+#define PyWeakref_GET_OBJECT(ref) (((PyWeakReference *)(ref))->wr_object)
+
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* !Py_WEAKREFOBJECT_H */