added a wrapper type for weak references

docs/api_core.rst

@@ -905,7 +905,6 @@ Wrapper classes
 
       Return the size in bytes.
 
-
 .. cpp:class:: type_object: public object
 
    Wrapper class representing Python ``type`` instances.
@@ -1020,6 +1019,15 @@ Wrapper classes
 
    Wrapper class representing a callable Python object.
 
+.. cpp:class:: weakref: public object
+
+   Wrapper class representing a Python weak reference object.
+
+   .. cpp:function:: explicit weakref(handle obj, handle callback = { })
+
+      Construct a new weak reference that points to `obj`. If provided,
+      Python will invoke the callable `callback` when `obj` expires.
+
 .. cpp:class:: args : public tuple
 
    Variable argument keyword list for use in function argument declarations.

docs/exchanging.rst

@@ -387,6 +387,7 @@ directives:
 :cpp:class:`iterator`, :cpp:class:`list`, :cpp:class:`mapping`,
 :cpp:class:`module_`, :cpp:class:`object`, :cpp:class:`sequence`,
 :cpp:class:`slice`, :cpp:class:`str`, :cpp:class:`tuple`,
+:cpp:class:`weakref`,
 :cpp:class:`type_object`, :cpp:class:`type_object_t\<T\> <handle_t>`,
 :cpp:class:`args`, and :cpp:class:`kwargs`.
 

include/nanobind/nb_types.h

@@ -611,6 +611,17 @@ class callable : public object {
     using object::object;
 };
 
+class weakref : public object {
+public:
+    NB_OBJECT(weakref, object, "weakref", PyWeakref_Check)
+
+    explicit weakref(handle obj, handle callback = {})
+        : object(PyWeakref_NewRef(obj.ptr(), callback.ptr()), detail::steal_t{}) {
+        if (!m_ptr)
+            detail::raise_python_error();
+    }
+};
+
 template <typename T> class handle_t : public handle {
 public:
     static constexpr auto Name = detail::make_caster<T>::Name;