Merge pull request #425 from dean0x7d/accessors

Make the accessor interface more complete

docs/changelog.rst

@@ -53,6 +53,8 @@ Breaking changes queued for v2.0.0 (Not yet released)
 * Added ``py::dict`` keyword constructor:``auto d = dict("number"_a=42, "name"_a="World");``
 * Added ``py::str::format()`` method and ``_s`` literal:
   ``py::str s = "1 + 2 = {}"_s.format(3);``
+* Attribute and item accessors now have a more complete interface which makes it possible
+  to chain attributes ``obj.attr("a")[key].attr("b").attr("method")(1, 2, 3)```.
 * Various minor improvements of library internals (no user-visible changes)
 
 1.8.1 (July 12, 2016)

include/pybind11/attr.h

@@ -276,7 +276,7 @@ template <> struct process_attribute<arg_v> : process_attribute_default<arg_v> {
 
 /// Process a parent class attribute
 template <typename T>
-struct process_attribute<T, enable_if_t<std::is_base_of<handle, T>::value>> : process_attribute_default<handle> {
+struct process_attribute<T, enable_if_t<is_pyobject<T>::value>> : process_attribute_default<handle> {
     static void init(const handle &h, type_record *r) { r->bases.append(h); }
 };
 

include/pybind11/cast.h

@@ -39,7 +39,10 @@ PYBIND11_NOINLINE inline internals &get_internals() {
         return *internals_ptr;
     handle builtins(PyEval_GetBuiltins());
     const char *id = PYBIND11_INTERNALS_ID;
-    capsule caps(builtins[id]);
+    capsule caps;
+    if (builtins.contains(id)) {
+        caps = builtins[id];
+    }
     if (caps.check()) {
         internals_ptr = caps;
     } else {
@@ -908,7 +911,7 @@ template <> struct handle_type_name<args> { static PYBIND11_DESCR name() { retur
 template <> struct handle_type_name<kwargs> { static PYBIND11_DESCR name() { return _("**kwargs"); } };
 
 template <typename type>
-struct type_caster<type, enable_if_t<std::is_base_of<handle, type>::value>> {
+struct type_caster<type, enable_if_t<is_pyobject<type>::value>> {
 public:
     template <typename T = type, enable_if_t<!std::is_base_of<object, T>::value, int> = 0>
     bool load(handle src, bool /* convert */) { value = type(src); return value.check(); }
@@ -1216,12 +1219,12 @@ private:
 
     void process(list &args_list, detail::args_proxy ap) {
         for (const auto &a : ap) {
-            args_list.append(a.cast<object>());
+            args_list.append(a);
         }
     }
 
     void process(list &/*args_list*/, arg_v a) {
-        if (m_kwargs[a.name]) {
+        if (m_kwargs.contains(a.name)) {
 #if defined(NDEBUG)
             multiple_values_error();
 #else
@@ -1240,7 +1243,7 @@ private:
 
     void process(list &/*args_list*/, detail::kwargs_proxy kp) {
         for (const auto &k : dict(kp, true)) {
-            if (m_kwargs[k.first]) {
+            if (m_kwargs.contains(k.first)) {
 #if defined(NDEBUG)
                 multiple_values_error();
 #else
@@ -1296,18 +1299,20 @@ unpacking_collector<policy> collect_arguments(Args &&...args) {
     return { std::forward<Args>(args)... };
 }
 
-NAMESPACE_END(detail)
-
+template <typename Derived>
 template <return_value_policy policy, typename... Args>
-object handle::operator()(Args &&...args) const {
-    return detail::collect_arguments<policy>(std::forward<Args>(args)...).call(m_ptr);
+object object_api<Derived>::operator()(Args &&...args) const {
+    return detail::collect_arguments<policy>(std::forward<Args>(args)...).call(derived().ptr());
 }
 
-template <return_value_policy policy,
-          typename... Args> object handle::call(Args &&... args) const {
+template <typename Derived>
+template <return_value_policy policy, typename... Args>
+object object_api<Derived>::call(Args &&...args) const {
     return operator()<policy>(std::forward<Args>(args)...);
 }
 
+NAMESPACE_END(detail)
+
 #define PYBIND11_MAKE_OPAQUE(Type) \
     namespace pybind11 { namespace detail { \
         template<> class type_caster<Type> : public type_caster_base<Type> { }; \

include/pybind11/numpy.h

@@ -125,11 +125,11 @@ private:
 
     static npy_api lookup() {
         module m = module::import("numpy.core.multiarray");
-        object c = (object) m.attr("_ARRAY_API");
+        auto c = m.attr("_ARRAY_API");
 #if PY_MAJOR_VERSION >= 3
-        void **api_ptr = (void **) (c ? PyCapsule_GetPointer(c.ptr(), NULL) : nullptr);
+        void **api_ptr = (void **) PyCapsule_GetPointer(c.ptr(), NULL);
 #else
-        void **api_ptr = (void **) (c ? PyCObject_AsVoidPtr(c.ptr()) : nullptr);
+        void **api_ptr = (void **) PyCObject_AsVoidPtr(c.ptr());
 #endif
         npy_api api;
 #define DECL_NPY_API(Func) api.Func##_ = (decltype(api.Func##_)) api_ptr[API_##Func];
@@ -220,9 +220,7 @@ private:
         struct field_descr { PYBIND11_STR_TYPE name; object format; pybind11::int_ offset; };
         std::vector<field_descr> field_descriptors;
 
-        auto fields = attr("fields").cast<object>();
-        auto items = fields.attr("items").cast<object>();
-        for (auto field : items()) {
+        for (auto field : attr("fields").attr("items")()) {
             auto spec = object(field, true).cast<tuple>();
             auto name = spec[0].cast<pybind11::str>();
             auto format = spec[1].cast<tuple>()[0].cast<dtype>();

include/pybind11/pybind11.h

@@ -18,6 +18,7 @@
 #  pragma warning(disable: 4800) // warning C4800: 'int': forcing value to bool 'true' or 'false' (performance warning)
 #  pragma warning(disable: 4996) // warning C4996: The POSIX name for this item is deprecated. Instead, use the ISO C and C++ conformant name
 #  pragma warning(disable: 4702) // warning C4702: unreachable code
+#  pragma warning(disable: 4522) // warning C4522: multiple assignment operators specified
 #elif defined(__INTEL_COMPILER)
 #  pragma warning(push)
 #  pragma warning(disable: 186)   // pointless comparison of unsigned integer with zero
@@ -176,7 +177,7 @@ protected:
             if (a.descr)
                 a.descr = strdup(a.descr);
             else if (a.value)
-                a.descr = strdup(((std::string) ((object) handle(a.value).attr("__repr__"))().str()).c_str());
+                a.descr = strdup(a.value.attr("__repr__")().cast<std::string>().c_str());
         }
 
         auto const &registered_types = detail::get_internals().registered_types_cpp;
@@ -278,9 +279,11 @@ protected:
 
             object scope_module;
             if (rec->scope) {
-                scope_module = (object) rec->scope.attr("__module__");
-                if (!scope_module)
-                    scope_module = (object) rec->scope.attr("__name__");
+                if (hasattr(rec->scope, "__module__")) {
+                    scope_module = rec->scope.attr("__module__");
+                } else if (hasattr(rec->scope, "__name__")) {
+                    scope_module = rec->scope.attr("__name__");
+                }
             }
 
             m_ptr = PyCFunction_NewEx(rec->def, rec_capsule.ptr(), scope_module.ptr());
@@ -544,8 +547,8 @@ public:
 
     template <typename Func, typename... Extra>
     module &def(const char *name_, Func &&f, const Extra& ... extra) {
-        cpp_function func(std::forward<Func>(f), name(name_),
-                          sibling((handle) attr(name_)), scope(*this), extra...);
+        cpp_function func(std::forward<Func>(f), name(name_), scope(*this),
+                          sibling(getattr(*this, name_, none())), extra...);
         /* PyModule_AddObject steals a reference to 'func' */
         PyModule_AddObject(ptr(), name_, func.inc_ref().ptr());
         return *this;
@@ -588,16 +591,18 @@ protected:
         object name(PYBIND11_FROM_STRING(rec->name), false);
         object scope_module;
         if (rec->scope) {
-            scope_module = (object) rec->scope.attr("__module__");
-            if (!scope_module)
-                scope_module = (object) rec->scope.attr("__name__");
+            if (hasattr(rec->scope, "__module__")) {
+                scope_module = rec->scope.attr("__module__");
+            } else if (hasattr(rec->scope, "__name__")) {
+                scope_module = rec->scope.attr("__name__");
+            }
         }
 
 #if PY_MAJOR_VERSION >= 3 && PY_MINOR_VERSION >= 3
         /* Qualified names for Python >= 3.3 */
         object scope_qualname;
-        if (rec->scope)
-            scope_qualname = (object) rec->scope.attr("__qualname__");
+        if (rec->scope && hasattr(rec->scope, "__qualname__"))
+            scope_qualname = rec->scope.attr("__qualname__");
         object ht_qualname;
         if (scope_qualname) {
             ht_qualname = object(PyUnicode_FromFormat(
@@ -719,8 +724,7 @@ protected:
         if (ob_type == &PyType_Type) {
             std::string name_ = std::string(ht_type.tp_name) + "__Meta";
 #if PY_MAJOR_VERSION >= 3 && PY_MINOR_VERSION >= 3
-            object ht_qualname(PyUnicode_FromFormat(
-                "%U__Meta", ((object) attr("__qualname__")).ptr()), false);
+            object ht_qualname(PyUnicode_FromFormat("%U__Meta", attr("__qualname__").ptr()), false);
 #endif
             object name(PYBIND11_FROM_STRING(name_.c_str()), false);
             object type_holder(PyType_Type.tp_alloc(&PyType_Type, 0), false);
@@ -894,17 +898,16 @@ public:
 
     template <typename Func, typename... Extra>
     class_ &def(const char *name_, Func&& f, const Extra&... extra) {
-        cpp_function cf(std::forward<Func>(f), name(name_),
-                        sibling(attr(name_)), is_method(*this),
-                        extra...);
+        cpp_function cf(std::forward<Func>(f), name(name_), is_method(*this),
+                        sibling(getattr(*this, name_, none())), extra...);
         attr(cf.name()) = cf;
         return *this;
     }
 
     template <typename Func, typename... Extra> class_ &
     def_static(const char *name_, Func f, const Extra&... extra) {
-        cpp_function cf(std::forward<Func>(f), name(name_),
-                        sibling(attr(name_)), scope(*this), extra...);
+        cpp_function cf(std::forward<Func>(f), name(name_), scope(*this),
+                        sibling(getattr(*this, name_, none())), extra...);
         attr(cf.name()) = cf;
         return *this;
     }
@@ -1336,19 +1339,19 @@ NAMESPACE_BEGIN(detail)
 PYBIND11_NOINLINE inline void print(tuple args, dict kwargs) {
     auto strings = tuple(args.size());
     for (size_t i = 0; i < args.size(); ++i) {
-        strings[i] = args[i].cast<object>().str();
+        strings[i] = args[i].str();
     }
-    auto sep = kwargs["sep"] ? kwargs["sep"] : cast(" ");
-    auto line = sep.attr("join").cast<object>()(strings);
+    auto sep = kwargs.contains("sep") ? kwargs["sep"] : cast(" ");
+    auto line = sep.attr("join")(strings);
 
-    auto file = kwargs["file"] ? kwargs["file"].cast<object>()
-                               : module::import("sys").attr("stdout");
-    auto write = file.attr("write").cast<object>();
+    auto file = kwargs.contains("file") ? kwargs["file"].cast<object>()
+                                        : module::import("sys").attr("stdout");
+    auto write = file.attr("write");
     write(line);
-    write(kwargs["end"] ? kwargs["end"] : cast("\n"));
+    write(kwargs.contains("end") ? kwargs["end"] : cast("\n"));
 
-    if (kwargs["flush"] && kwargs["flush"].cast<bool>()) {
-        file.attr("flush").cast<object>()();
+    if (kwargs.contains("flush") && kwargs["flush"].cast<bool>()) {
+        file.attr("flush")();
     }
 }
 NAMESPACE_END(detail)
@@ -1500,7 +1503,7 @@ inline function get_type_overload(const void *this_ptr, const detail::type_info
     if (cache.find(key) != cache.end())
         return function();
 
-    function overload = (function) py_object.attr(name);
+    function overload = getattr(py_object, name, function());
     if (overload.is_cpp_function()) {
         cache.insert(key);
         return function();

include/pybind11/pytypes.h

@@ -16,50 +16,88 @@
 NAMESPACE_BEGIN(pybind11)
 
 /* A few forward declarations */
-class object; class str; class iterator;
+class handle; class object;
+class str; class iterator;
 struct arg; struct arg_v;
-namespace detail { class accessor; class args_proxy; class kwargs_proxy; }
+
+NAMESPACE_BEGIN(detail)
+class args_proxy;
+
+// Accessor forward declarations
+template <typename Policy> class accessor;
+namespace accessor_policies {
+    struct obj_attr;
+    struct str_attr;
+    struct generic_item;
+    struct list_item;
+    struct tuple_item;
+}
+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 list_accessor = accessor<accessor_policies::list_item>;
+using tuple_accessor = accessor<accessor_policies::tuple_item>;
+
+/// Tag and check to identify a class which implements the Python object API
+class pyobject_tag { };
+template <typename T> using is_pyobject = std::is_base_of<pyobject_tag, T>;
+
+/// Mixin which adds common functions to handle, object and various accessors.
+/// The only requirement for `Derived` is to implement `PyObject *Derived::ptr() const`.
+template <typename Derived>
+class object_api : public pyobject_tag {
+    const Derived &derived() const { return static_cast<const Derived &>(*this); }
+
+public:
+    iterator begin() const;
+    iterator end() const;
+    item_accessor operator[](handle key) const;
+    item_accessor operator[](const char *key) const;
+    obj_attr_accessor attr(handle key) const;
+    str_attr_accessor attr(const char *key) const;
+    args_proxy operator*() const;
+    template <typename T> bool contains(T &&key) const;
+
+    template <return_value_policy policy = return_value_policy::automatic_reference, typename... Args>
+    object operator()(Args &&...args) const;
+    template <return_value_policy policy = return_value_policy::automatic_reference, typename... Args>
+    PYBIND11_DEPRECATED("call(...) was deprecated in favor of operator()(...)")
+        object call(Args&&... args) const;
+
+    bool is_none() const { return derived().ptr() == Py_None; }
+    pybind11::str str() const;
+    pybind11::str repr() const;
+
+    int ref_count() const { return static_cast<int>(Py_REFCNT(derived().ptr())); }
+    handle get_type() const;
+};
+
+NAMESPACE_END(detail)
 
 /// Holds a reference to a Python object (no reference counting)
-class handle {
+class handle : public detail::object_api<handle> {
 public:
-    handle() : m_ptr(nullptr) { }
-    handle(const handle &other) : m_ptr(other.m_ptr) { }
+    handle() = default;
     handle(PyObject *ptr) : m_ptr(ptr) { }
+
     PyObject *ptr() const { return m_ptr; }
     PyObject *&ptr() { return m_ptr; }
     const handle& inc_ref() const { Py_XINCREF(m_ptr); return *this; }
     const handle& dec_ref() const { Py_XDECREF(m_ptr); return *this; }
-    int ref_count() const { return (int) Py_REFCNT(m_ptr); }
-    handle get_type() const { return handle((PyObject *) Py_TYPE(m_ptr)); }
-    inline iterator begin() const;
-    inline iterator end() const;
-    inline detail::accessor operator[](handle key) const;
-    inline detail::accessor operator[](const char *key) const;
-    inline detail::accessor attr(handle key) const;
-    inline detail::accessor attr(const char *key) const;
-    inline pybind11::str str() const;
-    inline pybind11::str repr() const;
-    bool is_none() const { return m_ptr == Py_None; }
+
     template <typename T> T cast() const;
-    template <return_value_policy policy = return_value_policy::automatic_reference, typename ... Args>
-    PYBIND11_DEPRECATED("call(...) was deprecated in favor of operator()(...)")
-        object call(Args&&... args) const;
-    template <return_value_policy policy = return_value_policy::automatic_reference, typename ... Args>
-    object operator()(Args&&... args) const;
     operator bool() const { return m_ptr != nullptr; }
     bool operator==(const handle &h) const { return m_ptr == h.m_ptr; }
     bool operator!=(const handle &h) const { return m_ptr != h.m_ptr; }
     bool check() const { return m_ptr != nullptr; }
-    inline detail::args_proxy operator*() const;
 protected:
-    PyObject *m_ptr;
+    PyObject *m_ptr = nullptr;
 };
 
 /// Holds a reference to a Python object (with reference counting)
 class object : public handle {
 public:
-    object() { }
+    object() = default;
     object(const object &o) : handle(o) { inc_ref(); }
     object(const handle &h, bool borrowed) : handle(h) { if (borrowed) inc_ref(); }
     object(PyObject *ptr, bool borrowed) : handle(ptr) { if (borrowed) inc_ref(); }
@@ -95,6 +133,52 @@ public:
     template <typename T> T cast() &&;
 };
 
+inline bool hasattr(handle obj, handle name) {
+    return PyObject_HasAttr(obj.ptr(), name.ptr()) == 1;
+}
+
+inline bool hasattr(handle obj, const char *name) {
+    return PyObject_HasAttrString(obj.ptr(), name) == 1;
+}
+
+inline object getattr(handle obj, handle name) {
+    PyObject *result = PyObject_GetAttr(obj.ptr(), name.ptr());
+    if (!result) { throw error_already_set(); }
+    return {result, false};
+}
+
+inline object getattr(handle obj, const char *name) {
+    PyObject *result = PyObject_GetAttrString(obj.ptr(), name);
+    if (!result) { throw error_already_set(); }
+    return {result, false};
+}
+
+inline object getattr(handle obj, handle name, handle default_) {
+    if (PyObject *result = PyObject_GetAttr(obj.ptr(), name.ptr())) {
+        return {result, false};
+    } else {
+        PyErr_Clear();
+        return {default_, true};
+    }
+}
+
+inline object getattr(handle obj, const char *name, handle default_) {
+    if (PyObject *result = PyObject_GetAttrString(obj.ptr(), name)) {
+        return {result, false};
+    } else {
+        PyErr_Clear();
+        return {default_, true};
+    }
+}
+
+inline void setattr(handle obj, handle name, handle value) {
+    if (PyObject_SetAttr(obj.ptr(), name.ptr(), value.ptr()) != 0) { throw error_already_set(); }
+}
+
+inline void setattr(handle obj, const char *name, handle value) {
+    if (PyObject_SetAttrString(obj.ptr(), name, value.ptr()) != 0) { throw error_already_set(); }
+}
+
 NAMESPACE_BEGIN(detail)
 inline handle get_function(handle value) {
     if (value) {
@@ -108,100 +192,97 @@ inline handle get_function(handle value) {
     return value;
 }
 
-class accessor {
+template <typename Policy>
+class accessor : public object_api<accessor<Policy>> {
+    using key_type = typename Policy::key_type;
+
 public:
-    accessor(handle obj, handle key, bool attr)
-        : obj(obj), key(key, true), attr(attr) { }
-    accessor(handle obj, const char *key, bool attr)
-        : obj(obj), key(PyUnicode_FromString(key), false), attr(attr) { }
-    accessor(const accessor &a) : obj(a.obj), key(a.key), attr(a.attr) { }
-
-    void operator=(accessor o) { operator=(object(o)); }
-
-    void operator=(const handle &value) {
-        if (attr) {
-            if (PyObject_SetAttr(obj.ptr(), key.ptr(), value.ptr()) == -1)
-                throw error_already_set();
-        } else {
-            if (PyObject_SetItem(obj.ptr(), key.ptr(), value.ptr()) == -1)
-                throw error_already_set();
-        }
-    }
+    accessor(handle obj, key_type key) : obj(obj), key(std::move(key)) { }
 
-    operator object() const {
-        object result(attr ? PyObject_GetAttr(obj.ptr(), key.ptr())
-                           : PyObject_GetItem(obj.ptr(), key.ptr()), false);
-        if (!result) {PyErr_Clear(); }
-        return result;
-    }
+    void operator=(const accessor &a) && { std::move(*this).operator=(handle(a)); }
+    void operator=(const accessor &a) & { operator=(handle(a)); }
+    void operator=(const object &o) && { std::move(*this).operator=(handle(o)); }
+    void operator=(const object &o) & { operator=(handle(o)); }
+    void operator=(handle value) && { Policy::set(obj, key, value); }
+    void operator=(handle value) & { get_cache() = object(value, true); }
 
-    template <typename T> T cast() const { return operator object().cast<T>(); }
+    operator object() const { return get_cache(); }
+    PyObject *ptr() const { return get_cache().ptr(); }
+    template <typename T> T cast() const { return get_cache().template cast<T>(); }
 
-    operator bool() const {
-        if (attr) {
-            return (bool) PyObject_HasAttr(obj.ptr(), key.ptr());
-        } else {
-            object result(PyObject_GetItem(obj.ptr(), key.ptr()), false);
-            if (!result) PyErr_Clear();
-            return (bool) result;
-        }
-    };
+private:
+    object &get_cache() const {
+        if (!cache) { cache = Policy::get(obj, key); }
+        return cache;
+    }
 
 private:
     handle obj;
-    object key;
-    bool attr;
+    key_type key;
+    mutable object cache;
 };
 
-struct list_accessor {
-public:
-    list_accessor(handle list, size_t index) : list(list), index(index) { }
+NAMESPACE_BEGIN(accessor_policies)
+struct obj_attr {
+    using key_type = object;
+    static object get(handle obj, handle key) { return getattr(obj, key); }
+    static void set(handle obj, handle key, handle val) { setattr(obj, key, val); }
+};
 
-    void operator=(list_accessor o) { return operator=(object(o)); }
+struct str_attr {
+    using key_type = const char *;
+    static object get(handle obj, const char *key) { return getattr(obj, key); }
+    static void set(handle obj, const char *key, handle val) { setattr(obj, key, val); }
+};
 
-    void operator=(const handle &o) {
-        // PyList_SetItem steals a reference to 'o'
-        if (PyList_SetItem(list.ptr(), (ssize_t) index, o.inc_ref().ptr()) < 0)
-            pybind11_fail("Unable to assign value in Python list!");
-    }
+struct generic_item {
+    using key_type = object;
 
-    operator object() const {
-        PyObject *result = PyList_GetItem(list.ptr(), (ssize_t) index);
-        if (!result)
-            pybind11_fail("Unable to retrieve value from Python list!");
-        return object(result, true);
+    static object get(handle obj, handle key) {
+        PyObject *result = PyObject_GetItem(obj.ptr(), key.ptr());
+        if (!result) { throw error_already_set(); }
+        return {result, false};
     }
 
-    template <typename T> T cast() const { return operator object().cast<T>(); }
-private:
-    handle list;
-    size_t index;
+    static void set(handle obj, handle key, handle val) {
+        if (PyObject_SetItem(obj.ptr(), key.ptr(), val.ptr()) != 0) { throw error_already_set(); }
+    }
 };
 
-struct tuple_accessor {
-public:
-    tuple_accessor(handle tuple, size_t index) : tuple(tuple), index(index) { }
+struct list_item {
+    using key_type = size_t;
 
-    void operator=(tuple_accessor o) { return operator=(object(o)); }
+    static object get(handle obj, size_t index) {
+        PyObject *result = PyList_GetItem(obj.ptr(), static_cast<ssize_t>(index));
+        if (!result) { throw error_already_set(); }
+        return {result, true};
+    }
 
-    void operator=(const handle &o) {
-        // PyTuple_SetItem steals a referenceto 'o'
-        if (PyTuple_SetItem(tuple.ptr(), (ssize_t) index, o.inc_ref().ptr()) < 0)
-            pybind11_fail("Unable to assign value in Python tuple!");
+    static void set(handle obj, size_t index, handle val) {
+        // PyList_SetItem steals a reference to 'val'
+        if (PyList_SetItem(obj.ptr(), static_cast<ssize_t>(index), val.inc_ref().ptr()) != 0) {
+            throw error_already_set();
+        }
     }
+};
+
+struct tuple_item {
+    using key_type = size_t;
 
-    operator object() const {
-        PyObject *result = PyTuple_GetItem(tuple.ptr(), (ssize_t) index);
-        if (!result)
-            pybind11_fail("Unable to retrieve value from Python tuple!");
-        return object(result, true);
+    static object get(handle obj, size_t index) {
+        PyObject *result = PyTuple_GetItem(obj.ptr(), static_cast<ssize_t>(index));
+        if (!result) { throw error_already_set(); }
+        return {result, true};
     }
 
-    template <typename T> T cast() const { return operator object().cast<T>(); }
-private:
-    handle tuple;
-    size_t index;
+    static void set(handle obj, size_t index, handle val) {
+        // PyTuple_SetItem steals a reference to 'val'
+        if (PyTuple_SetItem(obj.ptr(), static_cast<ssize_t>(index), val.inc_ref().ptr()) != 0) {
+            throw error_already_set();
+        }
+    }
 };
+NAMESPACE_END(accessor_policies)
 
 struct dict_iterator {
 public:
@@ -347,14 +428,6 @@ public:
     PYBIND11_OBJECT_DEFAULT(iterable, object, detail::PyIterable_Check)
 };
 
-inline detail::accessor handle::operator[](handle key) const { return detail::accessor(*this, key, false); }
-inline detail::accessor handle::operator[](const char *key) const { return detail::accessor(*this, key, false); }
-inline detail::accessor handle::attr(handle key) const { return detail::accessor(*this, key, true); }
-inline detail::accessor handle::attr(const char *key) const { return detail::accessor(*this, key, true); }
-inline iterator handle::begin() const { return iterator(PyObject_GetIter(ptr()), false); }
-inline iterator handle::end() const { return iterator(nullptr, false); }
-inline detail::args_proxy handle::operator*() const { return detail::args_proxy(*this); }
-
 class bytes;
 
 class str : public object {
@@ -391,7 +464,7 @@ public:
 
     template <typename... Args>
     str format(Args &&...args) const {
-        return attr("format").cast<object>()(std::forward<Args>(args)...);
+        return attr("format")(std::forward<Args>(args)...);
     }
 };
 
@@ -400,24 +473,6 @@ inline namespace literals {
 inline str operator"" _s(const char *s, size_t size) { return {s, size}; }
 }
 
-inline pybind11::str handle::str() const {
-    PyObject *strValue = PyObject_Str(m_ptr);
-#if PY_MAJOR_VERSION < 3
-    PyObject *unicode = PyUnicode_FromEncodedObject(strValue, "utf-8", nullptr);
-    Py_XDECREF(strValue); strValue = unicode;
-#endif
-    return pybind11::str(strValue, false);
-}
-
-inline pybind11::str handle::repr() const {
-    PyObject *strValue = PyObject_Repr(m_ptr);
-#if PY_MAJOR_VERSION < 3
-    PyObject *unicode = PyUnicode_FromEncodedObject(strValue, "utf-8", nullptr);
-    Py_XDECREF(strValue); strValue = unicode;
-#endif
-    return pybind11::str(strValue, false);
-}
-
 class bytes : public object {
 public:
     PYBIND11_OBJECT_DEFAULT(bytes, object, PYBIND11_BYTES_CHECK)
@@ -583,7 +638,7 @@ public:
         if (!m_ptr) pybind11_fail("Could not allocate tuple object!");
     }
     size_t size() const { return (size_t) PyTuple_Size(m_ptr); }
-    detail::tuple_accessor operator[](size_t index) const { return detail::tuple_accessor(*this, index); }
+    detail::tuple_accessor operator[](size_t index) const { return {*this, index}; }
 };
 
 class dict : public object {
@@ -602,6 +657,8 @@ public:
     detail::dict_iterator begin() const { return (++detail::dict_iterator(*this, 0)); }
     detail::dict_iterator end() const { return detail::dict_iterator(); }
     void clear() const { PyDict_Clear(ptr()); }
+    bool contains(handle key) const { return PyDict_Contains(ptr(), key.ptr()) == 1; }
+    bool contains(const char *key) const { return PyDict_Contains(ptr(), pybind11::str(key).ptr()) == 1; }
 };
 
 class list : public object {
@@ -611,7 +668,7 @@ public:
         if (!m_ptr) pybind11_fail("Could not allocate list object!");
     }
     size_t size() const { return (size_t) PyList_Size(m_ptr); }
-    detail::list_accessor operator[](size_t index) const { return detail::list_accessor(*this, index); }
+    detail::list_accessor operator[](size_t index) const { return {*this, index}; }
     void append(handle h) const { PyList_Append(m_ptr, h.ptr()); }
 };
 
@@ -691,4 +748,40 @@ inline size_t len(handle h) {
     return (size_t) result;
 }
 
+NAMESPACE_BEGIN(detail)
+template <typename D> iterator object_api<D>::begin() const { return {PyObject_GetIter(derived().ptr()), false}; }
+template <typename D> iterator object_api<D>::end() const { return {nullptr, false}; }
+template <typename D> item_accessor object_api<D>::operator[](handle key) const { return {derived(), object(key, true)}; }
+template <typename D> item_accessor object_api<D>::operator[](const char *key) const { return {derived(), pybind11::str(key)}; }
+template <typename D> obj_attr_accessor object_api<D>::attr(handle key) const { return {derived(), object(key, true)}; }
+template <typename D> str_attr_accessor object_api<D>::attr(const char *key) const { return {derived(), key}; }
+template <typename D> args_proxy object_api<D>::operator*() const { return {derived().ptr()}; }
+template <typename D> template <typename T> bool object_api<D>::contains(T &&key) const {
+    return attr("__contains__")(std::forward<T>(key)).template cast<bool>();
+}
+
+template <typename D>
+pybind11::str object_api<D>::str() const {
+    PyObject *str_value = PyObject_Str(derived().ptr());
+#if PY_MAJOR_VERSION < 3
+    PyObject *unicode = PyUnicode_FromEncodedObject(str_value, "utf-8", nullptr);
+    Py_XDECREF(str_value); str_value = unicode;
+#endif
+    return {str_value, false};
+}
+
+template <typename D>
+pybind11::str object_api<D>::repr() const {
+    PyObject *str_value = PyObject_Repr(derived().ptr());
+#if PY_MAJOR_VERSION < 3
+    PyObject *unicode = PyUnicode_FromEncodedObject(str_value, "utf-8", nullptr);
+    Py_XDECREF(str_value); str_value = unicode;
+#endif
+    return {str_value, false};
+}
+
+template <typename D>
+handle object_api<D>::get_type() const { return (PyObject *) Py_TYPE(derived().ptr()); }
+
+NAMESPACE_END(detail)
 NAMESPACE_END(pybind11)

tests/constructor_stats.h

@@ -103,7 +103,7 @@ public:
 
     int alive() {
         // Force garbage collection to ensure any pending destructors are invoked:
-        py::module::import("gc").attr("collect").operator py::object()();
+        py::module::import("gc").attr("collect")();
         int total = 0;
         for (const auto &p : _instances) if (p.second > 0) total += p.second;
         return total;

tests/pybind11_tests.cpp

@@ -39,7 +39,7 @@ PYBIND11_PLUGIN(pybind11_tests) {
     for (const auto &initializer : initializers())
         initializer(m);
 
-    if (!m.attr("have_eigen")) m.attr("have_eigen") = py::cast(false);
+    if (!py::hasattr(m, "have_eigen")) m.attr("have_eigen") = py::cast(false);
 
     return m.ptr();
 }

tests/test_python_types.cpp

@@ -60,7 +60,7 @@ public:
     py::list get_list() {
         py::list list;
         list.append(py::str("value"));
-        py::print("Entry at position 0:", py::object(list[0]));
+        py::print("Entry at position 0:", list[0]);
         list[0] = py::str("overwritten");
         return list;
     }
@@ -203,7 +203,7 @@ test_initializer python_types([](py::module &m) {
         py::print("no new line here", "end"_a=" -- ");
         py::print("next print");
 
-        auto py_stderr = py::module::import("sys").attr("stderr").cast<py::object>();
+        auto py_stderr = py::module::import("sys").attr("stderr");
         py::print("this goes to stderr", "file"_a=py_stderr);
 
         py::print("flush", "flush"_a=true);
@@ -222,4 +222,71 @@ test_initializer python_types([](py::module &m) {
         auto d2 = py::dict("z"_a=3, **d1);
         return d2;
     });
+
+    m.def("test_accessor_api", [](py::object o) {
+        auto d = py::dict();
+
+        d["basic_attr"] = o.attr("basic_attr");
+
+        auto l = py::list();
+        for (const auto &item : o.attr("begin_end")) {
+            l.append(item);
+        }
+        d["begin_end"] = l;
+
+        d["operator[object]"] = o.attr("d")["operator[object]"_s];
+        d["operator[char *]"] = o.attr("d")["operator[char *]"];
+
+        d["attr(object)"] = o.attr("sub").attr("attr_obj");
+        d["attr(char *)"] = o.attr("sub").attr("attr_char");
+        try {
+            o.attr("sub").attr("missing").ptr();
+        } catch (const py::error_already_set &) {
+            d["missing_attr_ptr"] = "raised"_s;
+        }
+        try {
+            o.attr("missing").attr("doesn't matter");
+        } catch (const py::error_already_set &) {
+            d["missing_attr_chain"] = "raised"_s;
+        }
+
+        d["is_none"] = py::cast(o.attr("basic_attr").is_none());
+
+        d["operator()"] = o.attr("func")(1);
+        d["operator*"] = o.attr("func")(*o.attr("begin_end"));
+
+        return d;
+    });
+
+    m.def("test_tuple_accessor", [](py::tuple existing_t) {
+        try {
+            existing_t[0] = py::cast(1);
+        } catch (const py::error_already_set &) {
+            // --> Python system error
+            // Only new tuples (refcount == 1) are mutable
+            auto new_t = py::tuple(3);
+            for (size_t i = 0; i < new_t.size(); ++i) {
+                new_t[i] = py::cast(i);
+            }
+            return new_t;
+        }
+        return py::tuple();
+    });
+
+    m.def("test_accessor_assignment", []() {
+        auto l = py::list(1);
+        l[0] = py::cast(0);
+
+        auto d = py::dict();
+        d["get"] = l[0];
+        auto var = l[0];
+        d["deferred_get"] = var;
+        l[0] = py::cast(1);
+        d["set"] = l[0];
+        var = py::cast(99); // this assignment should not overwrite l[0]
+        d["deferred_set"] = l[0];
+        d["var"] = var;
+
+        return d;
+    });
 });

tests/test_python_types.py

@@ -248,3 +248,42 @@ def test_dict_api():
     from pybind11_tests import test_dict_keyword_constructor
 
     assert test_dict_keyword_constructor() == {"x": 1, "y": 2, "z": 3}
+
+
+def test_accessors():
+    from pybind11_tests import test_accessor_api, test_tuple_accessor, test_accessor_assignment
+
+    class SubTestObject:
+        attr_obj = 1
+        attr_char = 2
+
+    class TestObject:
+        basic_attr = 1
+        begin_end = [1, 2, 3]
+        d = {"operator[object]": 1, "operator[char *]": 2}
+        sub = SubTestObject()
+
+        def func(self, x, *args):
+            return self.basic_attr + x + sum(args)
+
+    d = test_accessor_api(TestObject())
+    assert d["basic_attr"] == 1
+    assert d["begin_end"] == [1, 2, 3]
+    assert d["operator[object]"] == 1
+    assert d["operator[char *]"] == 2
+    assert d["attr(object)"] == 1
+    assert d["attr(char *)"] == 2
+    assert d["missing_attr_ptr"] == "raised"
+    assert d["missing_attr_chain"] == "raised"
+    assert d["is_none"] is False
+    assert d["operator()"] == 2
+    assert d["operator*"] == 7
+
+    assert test_tuple_accessor(tuple()) == (0, 1, 2)
+
+    d = test_accessor_assignment()
+    assert d["get"] == 0
+    assert d["deferred_get"] == 0
+    assert d["set"] == 1
+    assert d["deferred_set"] == 1
+    assert d["var"] == 99