added nb::del mirroring the Python del statement

docs/api_core.rst

@@ -563,6 +563,24 @@ Attribute access
    Equivalent to ``del h.key`` and ``delattr(h, key)`` in Python.
    Raises :cpp:class:`python_error` if the operation fails.
 
+.. cpp:function:: template <typename T> void del(detail::accessor<T> &)
+
+   Remove an element from a sequence or mapping. The C++ statement
+
+   .. code-block:: cpp
+
+      nb::del(o[key]);
+
+   is equivalent to ``del o[key]`` in Python.
+
+   When the element cannot be removed, the function will raise
+   :cpp:class:`python_error` wrapping either a Python ``IndexError`` (for
+   sequence types) or a ``KeyError`` (for mapping types).
+
+.. cpp:function:: template <typename T> void del(detail::accessor<T> &&)
+
+   Rvalue equivalent of the above expression.
+
 Size queries
 ------------
 
@@ -672,6 +690,8 @@ Wrapper classes
    read and write list elements (the bindings for this operator are provided by
    the parent class and not listed here).
 
+   Use the :cpp:func:`nb::del <del>` function to remove elements.
+
    .. cpp:function:: list()
 
       Create an empty list
@@ -718,6 +738,8 @@ Wrapper classes
    elements (the bindings for this operator are provided by the parent class
    and not listed here).
 
+   Use the :cpp:func:`nb::del <del>` function to remove elements.
+
    .. cpp:function:: dict()
 
       Create an empty dictionary

docs/changelog.rst

@@ -21,6 +21,16 @@ Version 1.7.0 (TBA)
 * Added :cpp:func:`nb::globals() <globals>`. (PR `#311
   <https://github.com/wjakob/nanobind/pull/311>`__).
 
+* Added :cpp:func:`nb::del() <del>` that takes an arbitrary accessor object.
+  With this new function, the C++ statement
+
+  .. code-block:: cpp
+
+     nb::del(o[key]);
+
+  is equivalent to ``del o[key]`` in Python.
+
+
 Version 1.6.2 (Oct 3, 2023)
 -------------------
 

include/nanobind/nb_accessor.h

@@ -11,6 +11,8 @@ NAMESPACE_BEGIN(NB_NAMESPACE)
 NAMESPACE_BEGIN(detail)
 
 template <typename Impl> class accessor : public api<accessor<Impl>> {
+    template <typename T> friend void nanobind::del(accessor<T> &);
+    template <typename T> friend void nanobind::del(accessor<T> &&);
 public:
     static constexpr auto Name = const_name("object");
 
@@ -35,6 +37,9 @@ template <typename Impl> class accessor : public api<accessor<Impl>> {
     NB_INLINE handle base() const { return m_base; }
     NB_INLINE object key() const { return steal(Impl::key(m_key)); }
 
+private:
+    NB_INLINE void del () { Impl::del(m_base, m_key); }
+
 private:
     PyObject *m_base;
     mutable PyObject *m_cache{nullptr};
@@ -87,6 +92,10 @@ struct str_item {
     NB_INLINE static void set(PyObject *obj, const char *key, PyObject *v) {
         setitem(obj, key, v);
     }
+
+    NB_INLINE static void del(PyObject *obj, const char *key) {
+        delitem(obj, key);
+    }
 };
 
 struct obj_item {
@@ -100,6 +109,10 @@ struct obj_item {
     NB_INLINE static void set(PyObject *obj, handle key, PyObject *v) {
         setitem(obj, key.ptr(), v);
     }
+
+    NB_INLINE static void del(PyObject *obj, handle key) {
+        delitem(obj, key.ptr());
+    }
 };
 
 struct num_item {
@@ -113,6 +126,10 @@ struct num_item {
     NB_INLINE static void set(PyObject *obj, Py_ssize_t index, PyObject *v) {
         setitem(obj, index, v);
     }
+
+    NB_INLINE static void del(PyObject *obj, Py_ssize_t index) {
+        delitem(obj, index);
+    }
 };
 
 struct num_item_list {
@@ -134,6 +151,10 @@ struct num_item_list {
         Py_DECREF(old);
 #endif
     }
+
+    NB_INLINE static void del(PyObject *obj, Py_ssize_t index) {
+        delitem(obj, index);
+    }
 };
 
 struct num_item_tuple {

include/nanobind/nb_lib.h

@@ -175,6 +175,11 @@ NB_CORE void setitem(PyObject *obj, Py_ssize_t, PyObject *value);
 NB_CORE void setitem(PyObject *obj, const char *key, PyObject *value);
 NB_CORE void setitem(PyObject *obj, PyObject *key, PyObject *value);
 
+/// Set an item or raise an exception
+NB_CORE void delitem(PyObject *obj, Py_ssize_t);
+NB_CORE void delitem(PyObject *obj, const char *key);
+NB_CORE void delitem(PyObject *obj, PyObject *key);
+
 // ========================================================================
 
 /// Determine the length of a Python object

include/nanobind/nb_types.h

@@ -816,4 +816,7 @@ inline detail::fast_iterator list::end() const {
 }
 #endif
 
+template <typename T> void del(detail::accessor<T> &a) { a.del(); }
+template <typename T> void del(detail::accessor<T> &&a) { a.del(); }
+
 NAMESPACE_END(NB_NAMESPACE)

src/common.cpp

@@ -488,6 +488,36 @@ void setitem(PyObject *obj, PyObject *key, PyObject *value) {
         raise_python_error();
 }
 
+void delitem(PyObject *obj, Py_ssize_t key_) {
+    PyObject *key = PyLong_FromSsize_t(key_);
+    if (!key)
+        raise_python_error();
+
+    int rv = PyObject_DelItem(obj, key);
+    Py_DECREF(key);
+
+    if (rv)
+        raise_python_error();
+}
+
+void delitem(PyObject *obj, const char *key_) {
+    PyObject *key = PyUnicode_FromString(key_);
+    if (!key)
+        raise_python_error();
+
+    int rv = PyObject_DelItem(obj, key);
+    Py_DECREF(key);
+
+    if (rv)
+        raise_python_error();
+}
+
+void delitem(PyObject *obj, PyObject *key) {
+    int rv = PyObject_DelItem(obj, key);
+    if (rv)
+        raise_python_error();
+}
+
 // ========================================================================
 
 PyObject *str_from_obj(PyObject *o) {

tests/test_functions.cpp

@@ -236,4 +236,7 @@ NB_MODULE(test_functions_ext, m) {
     });
 
     m.def("test_set_contains", [](nb::set s, nb::handle h) { return s.contains(h); });
+
+    m.def("test_del_list", [](nb::list l) { nb::del(l[2]); });
+    m.def("test_del_dict", [](nb::dict l) { nb::del(l["a"]); });
 }

tests/test_functions.py

@@ -332,3 +332,19 @@ def test38_set():
     assert t.test_set_contains(x, '123')
     assert not t.test_set_contains(x, '1234')
     assert not t.test_set_contains(x, 1234)
+
+
+def test39_del():
+    l = [0,1,2,3,4]
+    t.test_del_list(l)
+    assert l == [0, 1, 3, 4]
+
+    l = {'a' : 0, 'b' : 1}
+    t.test_del_dict(l)
+    assert l == {'b' : 1}
+
+    with pytest.raises(IndexError):
+        t.test_del_list([])
+
+    with pytest.raises(KeyError):
+        t.test_del_dict({})