Add shortcut dict::get and optimize item access for dict

include/pybind11/detail/common.h

@@ -185,6 +185,7 @@
 #define PYBIND11_BOOL_ATTR "__bool__"
 #define PYBIND11_NB_BOOL(ptr) ((ptr)->nb_bool)
 #define PYBIND11_BUILTINS_MODULE "builtins"
+#define PYBIND11_DICT_GET_ITEM_WITH_ERROR PyDict_GetItemWithError
 // Providing a separate declaration to make Clang's -Wmissing-prototypes happy.
 // See comment for PYBIND11_MODULE below for why this is marked "maybe unused".
 #define PYBIND11_PLUGIN_IMPL(name) \
@@ -213,6 +214,7 @@
 #define PYBIND11_BOOL_ATTR "__nonzero__"
 #define PYBIND11_NB_BOOL(ptr) ((ptr)->nb_nonzero)
 #define PYBIND11_BUILTINS_MODULE "__builtin__"
+#define PYBIND11_DICT_GET_ITEM_WITH_ERROR _PyDict_GetItemWithError
 // Providing a separate PyInit decl to make Clang's -Wmissing-prototypes happy.
 // See comment for PYBIND11_MODULE below for why this is marked "maybe unused".
 #define PYBIND11_PLUGIN_IMPL(name) \

include/pybind11/pytypes.h

@@ -35,13 +35,15 @@ namespace accessor_policies {
     struct sequence_item;
     struct list_item;
     struct tuple_item;
+    struct dict_item;
 } // namespace accessor_policies
 using obj_attr_accessor = accessor<accessor_policies::obj_attr>;
 using str_attr_accessor = accessor<accessor_policies::str_attr>;
 using item_accessor = accessor<accessor_policies::generic_item>;
 using sequence_accessor = accessor<accessor_policies::sequence_item>;
 using list_accessor = accessor<accessor_policies::list_item>;
 using tuple_accessor = accessor<accessor_policies::tuple_item>;
+using dict_accessor = accessor<accessor_policies::dict_item>;
 
 /// Tag and check to identify a class which implements the Python object API
 class pyobject_tag { };
@@ -613,6 +615,30 @@ struct tuple_item {
         }
     }
 };
+
+struct dict_item {
+    using key_type = object;
+
+    static object get(handle obj, handle key) {
+        if (PyObject *result = PYBIND11_DICT_GET_ITEM_WITH_ERROR(obj.ptr(), key.ptr())) {
+            return reinterpret_borrow<object>(result);
+        } else {
+            // NULL with an exception means exception occurred when calling
+            // "__hash__" or "__eq__" on the key
+            // NULL without an exception means the key wasn’t present
+            if (!PyErr_Occurred())
+                // Synthesize a KeyError with the key
+                PyErr_SetObject(PyExc_KeyError, key.inc_ref().ptr());
+            throw error_already_set();
+        }
+    }
+
+    static void set(handle obj, handle key, handle val) {
+        if (PyDict_SetItem(obj.ptr(), key.ptr(), val.ptr()) != 0) {
+            throw error_already_set();
+        }
+    }
+};
 PYBIND11_NAMESPACE_END(accessor_policies)
 
 /// STL iterator template used for tuple, list, sequence and dict
@@ -1285,13 +1311,33 @@ class dict : public object {
 
     size_t size() const { return (size_t) PyDict_Size(m_ptr); }
     bool empty() const { return size() == 0; }
+    detail::dict_accessor operator[](const char *key) const { return {*this, pybind11::str(key)}; }
+    detail::dict_accessor operator[](handle h) const { return {*this, reinterpret_borrow<object>(h)}; }
     detail::dict_iterator begin() const { return {*this, 0}; }
     detail::dict_iterator end() const { return {}; }
     void clear() const { PyDict_Clear(ptr()); }
     template <typename T> bool contains(T &&key) const {
         return PyDict_Contains(m_ptr, detail::object_or_cast(std::forward<T>(key)).ptr()) == 1;
     }
 
+    object get(handle key, handle default_ = none()) const {
+        if (PyObject *result = PYBIND11_DICT_GET_ITEM_WITH_ERROR(m_ptr, key.ptr())) {
+            return reinterpret_borrow<object>(result);
+        } else {
+            // NULL with an exception means exception occurred when calling
+            // "__hash__" or "__eq__" on the key
+            if (PyErr_Occurred())
+                throw error_already_set();
+            // NULL without an exception means the key wasn’t present
+            else
+                return reinterpret_borrow<object>(default_);
+        }
+    }
+
+    object get(const char *key, handle default_ = none()) const {
+        return get(pybind11::str(key), default_);
+    }
+
 private:
     /// Call the `dict` Python type -- always returns a new reference
     static PyObject *raw_dict(PyObject *op) {

tests/test_pytypes.cpp

@@ -68,12 +68,24 @@ TEST_SUBMODULE(pytypes, m) {
         auto d2 = py::dict("z"_a=3, **d1);
         return d2;
     });
-    m.def("dict_contains", [](py::dict dict, py::object val) {
+    m.def("dict_contains", [](py::dict dict, const char* val) {
         return dict.contains(val);
     });
-    m.def("dict_contains", [](py::dict dict, const char* val) {
+    m.def("dict_contains", [](py::dict dict, py::object val) {
         return dict.contains(val);
     });
+    m.def("dict_get", [](py::dict dict, const char* key, py::object default_) {
+        return dict.get(key, default_);
+    });
+    m.def("dict_get", [](py::dict dict, py::object key, py::object default_) {
+        return dict.get(key, default_);
+    });
+    m.def("dict_get", [](py::dict dict, const char* key) {
+        return dict.get(key);
+    });
+    m.def("dict_get", [](py::dict dict, py::object key) {
+        return dict.get(key);
+    });
 
     // test_str
     m.def("str_from_string", []() { return py::str(std::string("baz")); });

tests/test_pytypes.py

@@ -92,6 +92,16 @@ def test_dict(capture, doc):
     assert m.dict_contains({42: None}, 42)
     assert m.dict_contains({"foo": None}, "foo")
 
+    d2 = {True: 42, 3: "abc", "abc": 3}
+    assert m.dict_get(d2, True) == 42
+    assert m.dict_get(d2, False) is None
+    assert m.dict_get(d2, 3, "def") == "abc"
+    assert m.dict_get(d2, 5, "def") == "def"
+    assert m.dict_get(d2, "abc") == 3
+    assert m.dict_get(d2, "def") is None
+    assert m.dict_get(d2, "abc", 5) == 3
+    assert m.dict_get(d2, "def", 5) == 5
+
     assert doc(m.get_dict) == "get_dict() -> dict"
     assert doc(m.print_dict) == "print_dict(arg0: dict) -> None"