Make all classes with the same instance size derive from a common base

In order to fully satisfy Python's inheritance type layout requirements,
all types should have a common 'solid' base. A solid base is one which
has the same instance size as the derived type (not counting the space
required for the optional `dict_ptr` and `weakrefs_ptr`). Thus, `object`
does not qualify as a solid base for pybind11 types and this can lead to
issues with multiple inheritance.

To get around this, new base types are created: one per unique instance
size. There is going to be very few of these bases. They ensure Python's
MRO checks will pass when multiple bases are involved.

include/pybind11/cast.h

@@ -26,6 +26,7 @@ struct type_info {
     PyTypeObject *type;
     size_t type_size;
     void (*init_holder)(PyObject *, const void *);
+    void (*dealloc)(PyObject *);
     std::vector<PyObject *(*)(PyObject *, PyTypeObject *)> implicit_conversions;
     std::vector<std::pair<const std::type_info *, void *(*)(void *)>> implicit_casts;
     std::vector<bool (*)(PyObject *, void *&)> *direct_conversions;

include/pybind11/class_support.h

@@ -85,6 +85,34 @@ inline PyTypeObject *make_static_property_type() {
 
 #endif // PYPY
 
+/** Inheriting from multiple C++ types in Python is not supported -- set an error instead.
+    A Python definition (`class C(A, B): pass`) will call `tp_new` so we check for multiple
+    C++ bases here. On the other hand, C++ type definitions (`py::class_<C, A, B>(m, "C")`)
+    don't not use `tp_new` and will not trigger this error. */
+extern "C" inline PyObject *pybind11_meta_new(PyTypeObject *metaclass, PyObject *args,
+                                              PyObject *kwargs) {
+    PyObject *bases = PyTuple_GetItem(args, 1); // arguments: (name, bases, dict)
+    if (!bases)
+        return nullptr;
+
+    auto &internals = get_internals();
+    auto num_cpp_bases = 0;
+    for (auto base : reinterpret_borrow<tuple>(bases)) {
+        auto base_type = (PyTypeObject *) base.ptr();
+        auto instance_size = static_cast<size_t>(base_type->tp_basicsize);
+        if (PyObject_IsSubclass(base.ptr(), internals.get_base(instance_size)))
+            ++num_cpp_bases;
+    }
+
+    if (num_cpp_bases > 1) {
+        PyErr_SetString(PyExc_TypeError, "Can't inherit from multiple C++ classes in Python."
+                                         "Use py::class_ to define the class in C++ instead.");
+        return nullptr;
+    } else {
+        return PyType_Type.tp_new(metaclass, args, kwargs);
+    }
+}
+
 /** Types with static properties need to handle `Type.static_prop = x` in a specific way.
     By default, Python replaces the `static_property` itself, but for wrapped C++ types
     we need to call `static_property.__set__()` in order to propagate the new value to
@@ -135,6 +163,8 @@ inline PyTypeObject* make_default_metaclass() {
     type->tp_name = name;
     type->tp_base = &PyType_Type;
     type->tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HEAPTYPE;
+
+    type->tp_new = pybind11_meta_new;
     type->tp_setattro = pybind11_meta_setattro;
 
     if (PyType_Ready(type) < 0)
@@ -143,5 +173,328 @@ inline PyTypeObject* make_default_metaclass() {
     return type;
 }
 
+/// Instance creation function for all pybind11 types. It only allocates space for the
+/// C++ object, but doesn't call the constructor -- an `__init__` function must do that.
+extern "C" inline PyObject *pybind11_object_new(PyTypeObject *type, PyObject *, PyObject *) {
+    PyObject *self = type->tp_alloc(type, 0);
+    auto instance = (instance_essentials<void> *) self;
+    auto tinfo = get_type_info(type);
+    instance->value = ::operator new(tinfo->type_size);
+    instance->owned = true;
+    instance->holder_constructed = false;
+    get_internals().registered_instances.emplace(instance->value, self);
+    return self;
+}
+
+/// An `__init__` function constructs the C++ object. Users should provide at least one
+/// of these using `py::init` or directly with `.def(__init__, ...)`. Otherwise, the
+/// following default function will be used which simply throws an exception.
+extern "C" inline int pybind11_object_init(PyObject *self, PyObject *, PyObject *) {
+    PyTypeObject *type = Py_TYPE(self);
+    std::string msg;
+#if defined(PYPY_VERSION)
+    msg += handle((PyObject *) type).attr("__module__").cast<std::string>() + ".";
+#endif
+    msg += type->tp_name;
+    msg += ": No constructor defined!";
+    PyErr_SetString(PyExc_TypeError, msg.c_str());
+    return -1;
+}
+
+/// Instance destructor function for all pybind11 types. It calls `type_info.dealloc`
+/// to destroy the C++ object itself, while the rest is Python bookkeeping.
+extern "C" inline void pybind11_object_dealloc(PyObject *self) {
+    auto instance = (instance_essentials<void> *) self;
+    if (instance->value) {
+        auto type = Py_TYPE(self);
+        get_type_info(type)->dealloc(self);
+
+        auto &registered_instances = get_internals().registered_instances;
+        auto range = registered_instances.equal_range(instance->value);
+        bool found = false;
+        for (auto it = range.first; it != range.second; ++it) {
+            if (type == Py_TYPE(it->second)) {
+                registered_instances.erase(it);
+                found = true;
+                break;
+            }
+        }
+        if (!found)
+            pybind11_fail("pybind11_object_dealloc(): Tried to deallocate unregistered instance!");
+
+        if (instance->weakrefs)
+            PyObject_ClearWeakRefs(self);
+
+        PyObject **dict_ptr = _PyObject_GetDictPtr(self);
+        if (dict_ptr)
+            Py_CLEAR(*dict_ptr);
+    }
+    Py_TYPE(self)->tp_free(self);
+}
+
+/** Create a type which can be used as a common base for all classes with the same
+    instance size, i.e. all classes with the same `sizeof(holder_type)`. This is
+    needed in order to satisfy Python's requirements for multiple inheritance.
+    Return value: New reference. */
+inline PyObject *make_object_base_type(size_t instance_size) {
+    auto name = "pybind11_object_" + std::to_string(instance_size);
+    auto name_obj = reinterpret_steal<object>(PYBIND11_FROM_STRING(name.c_str()));
+
+    /* Danger zone: from now (and until PyType_Ready), make sure to
+       issue no Python C API calls which could potentially invoke the
+       garbage collector (the GC will call type_traverse(), which will in
+       turn find the newly constructed type in an invalid state) */
+    auto heap_type = (PyHeapTypeObject *) PyType_Type.tp_alloc(&PyType_Type, 0);
+    if (!heap_type)
+        pybind11_fail("make_object_base_type(): error allocating type!");
+
+    heap_type->ht_name = name_obj.inc_ref().ptr();
+#if PY_MAJOR_VERSION >= 3 && PY_MINOR_VERSION >= 3
+    heap_type->ht_qualname = name_obj.inc_ref().ptr();
+#endif
+
+    auto type = &heap_type->ht_type;
+    type->tp_name = strdup(name.c_str());
+    type->tp_base = &PyBaseObject_Type;
+    type->tp_basicsize = static_cast<ssize_t>(instance_size);
+    type->tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HEAPTYPE;
+
+    type->tp_new = pybind11_object_new;
+    type->tp_init = pybind11_object_init;
+    type->tp_dealloc = pybind11_object_dealloc;
+
+    /* Support weak references (needed for the keep_alive feature) */
+    type->tp_weaklistoffset = offsetof(instance_essentials<void>, weakrefs);
+
+    if (PyType_Ready(type) < 0)
+        pybind11_fail("PyType_Ready failed in make_object_base_type():" + error_string());
+
+    assert(!PyType_HasFeature(type, Py_TPFLAGS_HAVE_GC));
+    return (PyObject *) heap_type;
+}
+
+/** Return the appropriate base type for the given instance size. The results are cached
+    in `internals.bases` so that only a single base is ever created for any size value.
+    Return value: Borrowed reference. */
+inline PyObject *internals::get_base(size_t instance_size) {
+    auto it = bases.find(instance_size);
+    if (it != bases.end()) {
+        return it->second;
+    } else {
+        auto base = make_object_base_type(instance_size);
+        bases[instance_size] = base;
+        return base;
+    }
+}
+
+/// dynamic_attr: Support for `d = instance.__dict__`.
+extern "C" inline PyObject *pybind11_get_dict(PyObject *self, void *) {
+    PyObject *&dict = *_PyObject_GetDictPtr(self);
+    if (!dict)
+        dict = PyDict_New();
+    Py_XINCREF(dict);
+    return dict;
+}
+
+/// dynamic_attr: Support for `instance.__dict__ = dict()`.
+extern "C" inline int pybind11_set_dict(PyObject *self, PyObject *new_dict, void *) {
+    if (!PyDict_Check(new_dict)) {
+        PyErr_Format(PyExc_TypeError, "__dict__ must be set to a dictionary, not a '%.200s'",
+                     Py_TYPE(new_dict)->tp_name);
+        return -1;
+    }
+    PyObject *&dict = *_PyObject_GetDictPtr(self);
+    Py_INCREF(new_dict);
+    Py_CLEAR(dict);
+    dict = new_dict;
+    return 0;
+}
+
+/// dynamic_attr: Allow the garbage collector to traverse the internal instance `__dict__`.
+extern "C" inline int pybind11_traverse(PyObject *self, visitproc visit, void *arg) {
+    PyObject *&dict = *_PyObject_GetDictPtr(self);
+    Py_VISIT(dict);
+    return 0;
+}
+
+/// dynamic_attr: Allow the GC to clear the dictionary.
+extern "C" inline int pybind11_clear(PyObject *self) {
+    PyObject *&dict = *_PyObject_GetDictPtr(self);
+    Py_CLEAR(dict);
+    return 0;
+}
+
+/// Give instances of this type a `__dict__` and opt into garbage collection.
+inline void enable_dynamic_attributes(PyHeapTypeObject *heap_type) {
+    auto type = &heap_type->ht_type;
+#if defined(PYPY_VERSION)
+    pybind11_fail(std::string(type->tp_name) + ": dynamic attributes are "
+                                               "currently not supported in "
+                                               "conjunction with PyPy!");
+#endif
+    type->tp_flags |= Py_TPFLAGS_HAVE_GC;
+    type->tp_dictoffset = type->tp_basicsize; // place dict at the end
+    type->tp_basicsize += sizeof(PyObject *); // and allocate enough space for it
+    type->tp_traverse = pybind11_traverse;
+    type->tp_clear = pybind11_clear;
+
+    static PyGetSetDef getset[] = {
+        {const_cast<char*>("__dict__"), pybind11_get_dict, pybind11_set_dict, nullptr, nullptr},
+        {nullptr, nullptr, nullptr, nullptr, nullptr}
+    };
+    type->tp_getset = getset;
+}
+
+/// buffer_protocol: Fill in the view as specified by flags.
+extern "C" inline int pybind11_getbuffer(PyObject *obj, Py_buffer *view, int flags) {
+    auto tinfo = get_type_info(Py_TYPE(obj));
+    if (view == nullptr || obj == nullptr || !tinfo || !tinfo->get_buffer) {
+        if (view)
+            view->obj = nullptr;
+        PyErr_SetString(PyExc_BufferError, "generic_type::getbuffer(): Internal error");
+        return -1;
+    }
+    memset(view, 0, sizeof(Py_buffer));
+    buffer_info *info = tinfo->get_buffer(obj, tinfo->get_buffer_data);
+    view->obj = obj;
+    view->ndim = 1;
+    view->internal = info;
+    view->buf = info->ptr;
+    view->itemsize = (ssize_t) info->itemsize;
+    view->len = view->itemsize;
+    for (auto s : info->shape)
+        view->len *= s;
+    if ((flags & PyBUF_FORMAT) == PyBUF_FORMAT)
+        view->format = const_cast<char *>(info->format.c_str());
+    if ((flags & PyBUF_STRIDES) == PyBUF_STRIDES) {
+        view->ndim = (int) info->ndim;
+        view->strides = (ssize_t *) &info->strides[0];
+        view->shape = (ssize_t *) &info->shape[0];
+    }
+    Py_INCREF(view->obj);
+    return 0;
+}
+
+/// buffer_protocol: Release the resources of the buffer.
+extern "C" inline void pybind11_releasebuffer(PyObject *, Py_buffer *view) {
+    delete (buffer_info *) view->internal;
+}
+
+/// Give this type a buffer interface.
+inline void enable_buffer_protocol(PyHeapTypeObject *heap_type) {
+    heap_type->ht_type.tp_as_buffer = &heap_type->as_buffer;
+#if PY_MAJOR_VERSION < 3
+    heap_type->ht_type.tp_flags |= Py_TPFLAGS_HAVE_NEWBUFFER;
+#endif
+
+    heap_type->as_buffer.bf_getbuffer = pybind11_getbuffer;
+    heap_type->as_buffer.bf_releasebuffer = pybind11_releasebuffer;
+}
+
+/** Create a brand new Python type according to the `type_record` specification.
+    Return value: New reference. */
+inline PyObject* make_new_python_type(const type_record &rec) {
+    auto name = reinterpret_steal<object>(PYBIND11_FROM_STRING(rec.name));
+
+#if PY_MAJOR_VERSION >= 3 && PY_MINOR_VERSION >= 3
+    auto ht_qualname = name;
+    if (rec.scope && hasattr(rec.scope, "__qualname__")) {
+        ht_qualname = reinterpret_steal<object>(
+            PyUnicode_FromFormat("%U.%U", rec.scope.attr("__qualname__").ptr(), name.ptr()));
+    }
+#endif
+
+    object module;
+    if (rec.scope) {
+        if (hasattr(rec.scope, "__module__"))
+            module = rec.scope.attr("__module__");
+        else if (hasattr(rec.scope, "__name__"))
+            module = rec.scope.attr("__name__");
+    }
+
+#if !defined(PYPY_VERSION)
+    const auto full_name = module ? str(module).cast<std::string>() + "." + rec.name
+                                  : std::string(rec.name);
+#else
+    const auto full_name = std::string(rec.name);
+#endif
+
+    char *tp_doc = nullptr;
+    if (rec.doc && options::show_user_defined_docstrings()) {
+        /* Allocate memory for docstring (using PyObject_MALLOC, since
+           Python will free this later on) */
+        size_t size = strlen(rec.doc) + 1;
+        tp_doc = (char *) PyObject_MALLOC(size);
+        memcpy((void *) tp_doc, rec.doc, size);
+    }
+
+    auto &internals = get_internals();
+    auto bases = tuple(rec.bases);
+    auto base = (bases.size() == 0) ? internals.get_base(rec.instance_size)
+                                    : bases[0].ptr();
+
+    /* Danger zone: from now (and until PyType_Ready), make sure to
+       issue no Python C API calls which could potentially invoke the
+       garbage collector (the GC will call type_traverse(), which will in
+       turn find the newly constructed type in an invalid state) */
+    auto heap_type = (PyHeapTypeObject *) PyType_Type.tp_alloc(&PyType_Type, 0);
+    if (!heap_type)
+        pybind11_fail(std::string(rec.name) + ": Unable to create type object!");
+
+    heap_type->ht_name = name.release().ptr();
+#if PY_MAJOR_VERSION >= 3 && PY_MINOR_VERSION >= 3
+    heap_type->ht_qualname = ht_qualname.release().ptr();
+#endif
+
+    auto type = &heap_type->ht_type;
+    type->tp_name = strdup(full_name.c_str());
+    type->tp_doc = tp_doc;
+    type->tp_base = (PyTypeObject *) handle(base).inc_ref().ptr();
+    type->tp_basicsize = static_cast<ssize_t>(rec.instance_size);
+    if (bases.size() > 0)
+        type->tp_bases = bases.release().ptr();
+
+    /* Don't inherit base __init__ */
+    type->tp_init = pybind11_object_init;
+
+    /* Custom metaclass if requested (used for static properties) */
+    if (rec.metaclass) {
+        Py_INCREF(internals.default_metaclass);
+        Py_TYPE(type) = (PyTypeObject *) internals.default_metaclass;
+    }
+
+    /* Supported protocols */
+    type->tp_as_number = &heap_type->as_number;
+    type->tp_as_sequence = &heap_type->as_sequence;
+    type->tp_as_mapping = &heap_type->as_mapping;
+
+    /* Flags */
+    type->tp_flags |= Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HEAPTYPE;
+#if PY_MAJOR_VERSION < 3
+    type->tp_flags |= Py_TPFLAGS_CHECKTYPES;
+#endif
+
+    if (rec.dynamic_attr)
+        enable_dynamic_attributes(heap_type);
+
+    if (rec.buffer_protocol)
+        enable_buffer_protocol(heap_type);
+
+    if (PyType_Ready(type) < 0)
+        pybind11_fail(std::string(rec.name) + ": PyType_Ready failed (" + error_string() + ")!");
+
+    assert(rec.dynamic_attr ? PyType_HasFeature(type, Py_TPFLAGS_HAVE_GC)
+                            : !PyType_HasFeature(type, Py_TPFLAGS_HAVE_GC));
+
+    /* Register type with the parent scope */
+    if (rec.scope)
+        setattr(rec.scope, rec.name, (PyObject *) type);
+
+    if (module) // Needed by pydoc
+        setattr((PyObject *) type, "__module__", module);
+
+    return (PyObject *) type;
+}
+
 NAMESPACE_END(detail)
 NAMESPACE_END(pybind11)

include/pybind11/common.h

@@ -122,7 +122,6 @@
 #define PYBIND11_SLICE_OBJECT PyObject
 #define PYBIND11_FROM_STRING PyUnicode_FromString
 #define PYBIND11_STR_TYPE ::pybind11::str
-#define PYBIND11_OB_TYPE(ht_type) (ht_type).ob_base.ob_base.ob_type
 #define PYBIND11_PLUGIN_IMPL(name) \
     extern "C" PYBIND11_EXPORT PyObject *PyInit_##name()
 #else
@@ -141,7 +140,6 @@
 #define PYBIND11_SLICE_OBJECT PySliceObject
 #define PYBIND11_FROM_STRING PyString_FromString
 #define PYBIND11_STR_TYPE ::pybind11::bytes
-#define PYBIND11_OB_TYPE(ht_type) (ht_type).ob_type
 #define PYBIND11_PLUGIN_IMPL(name) \
     static PyObject *pybind11_init_wrapper();               \
     extern "C" PYBIND11_EXPORT void init##name() {          \
@@ -363,10 +361,14 @@ struct internals {
     std::unordered_map<std::string, void *> shared_data; // Custom data to be shared across extensions
     PyTypeObject *static_property_type;
     PyTypeObject *default_metaclass;
+    std::unordered_map<size_t, PyObject *> bases; // one base type per `instance_size` (very few)
 #if defined(WITH_THREAD)
     decltype(PyThread_create_key()) tstate = 0; // Usually an int but a long on Cygwin64 with Python 3.x
     PyInterpreterState *istate = nullptr;
 #endif
+
+    /// Return the appropriate base type for the given instance size
+    PyObject *get_base(size_t instance_size);
 };
 
 /// Return a reference to the current 'internals' information

include/pybind11/pybind11.h

@@ -760,196 +760,39 @@ public:
 };
 
 NAMESPACE_BEGIN(detail)
-extern "C" inline PyObject *get_dict(PyObject *op, void *) {
-    PyObject *&dict = *_PyObject_GetDictPtr(op);
-    if (!dict)
-        dict = PyDict_New();
-    Py_XINCREF(dict);
-    return dict;
-}
-
-extern "C" inline int set_dict(PyObject *op, PyObject *new_dict, void *) {
-    if (!PyDict_Check(new_dict)) {
-        PyErr_Format(PyExc_TypeError, "__dict__ must be set to a dictionary, not a '%.200s'",
-                     Py_TYPE(new_dict)->tp_name);
-        return -1;
-    }
-    PyObject *&dict = *_PyObject_GetDictPtr(op);
-    Py_INCREF(new_dict);
-    Py_CLEAR(dict);
-    dict = new_dict;
-    return 0;
-}
-
-static PyGetSetDef generic_getset[] = {
-    {const_cast<char*>("__dict__"), get_dict, set_dict, nullptr, nullptr},
-    {nullptr, nullptr, nullptr, nullptr, nullptr}
-};
-
 /// Generic support for creating new Python heap types
 class generic_type : public object {
     template <typename...> friend class class_;
 public:
     PYBIND11_OBJECT_DEFAULT(generic_type, object, PyType_Check)
 protected:
-    void initialize(type_record *rec) {
+    void initialize(const type_record &rec) {
-        auto &internals = get_internals();
+        if (rec.scope && hasattr(rec.scope, rec.name))
-        auto tindex = std::type_index(*(rec->type));
+            pybind11_fail("generic_type: cannot initialize type \"" + std::string(rec.name) +
-
-        if (get_type_info(*(rec->type)))
-            pybind11_fail("generic_type: type \"" + std::string(rec->name) +
-                          "\" is already registered!");
-
-        auto name = reinterpret_steal<object>(PYBIND11_FROM_STRING(rec->name));
-        object scope_module;
-        if (rec->scope) {
-            if (hasattr(rec->scope, rec->name))
-                pybind11_fail("generic_type: cannot initialize type \"" + std::string(rec->name) +
                           "\": an object with that name is already defined");
 
-            if (hasattr(rec->scope, "__module__")) {
+        if (get_type_info(*rec.type))
-                scope_module = rec->scope.attr("__module__");
+            pybind11_fail("generic_type: type \"" + std::string(rec.name) +
-            } else if (hasattr(rec->scope, "__name__")) {
+                          "\" is already registered!");
-                scope_module = rec->scope.attr("__name__");
-            }
-        }
 
-#if PY_MAJOR_VERSION >= 3 && PY_MINOR_VERSION >= 3
+        m_ptr = make_new_python_type(rec);
-        /* Qualified names for Python >= 3.3 */
-        object scope_qualname;
-        if (rec->scope && hasattr(rec->scope, "__qualname__"))
-            scope_qualname = rec->scope.attr("__qualname__");
-        object ht_qualname;
-        if (scope_qualname)
-            ht_qualname = reinterpret_steal<object>(PyUnicode_FromFormat(
-                "%U.%U", scope_qualname.ptr(), name.ptr()));
-        else
-            ht_qualname = name;
-#endif
-
-#if !defined(PYPY_VERSION)
-        std::string full_name = (scope_module ? ((std::string) pybind11::str(scope_module) + "." + rec->name)
-                                              : std::string(rec->name));
-#else
-        std::string full_name = std::string(rec->name);
-#endif
-
-        size_t num_bases = rec->bases.size();
-        auto bases = tuple(rec->bases);
-
-        char *tp_doc = nullptr;
-        if (rec->doc && options::show_user_defined_docstrings()) {
-            /* Allocate memory for docstring (using PyObject_MALLOC, since
-               Python will free this later on) */
-            size_t size = strlen(rec->doc) + 1;
-            tp_doc = (char *) PyObject_MALLOC(size);
-            memcpy((void *) tp_doc, rec->doc, size);
-        }
-
-        /* Danger zone: from now (and until PyType_Ready), make sure to
-           issue no Python C API calls which could potentially invoke the
-           garbage collector (the GC will call type_traverse(), which will in
-           turn find the newly constructed type in an invalid state) */
-
-        auto type_holder = reinterpret_steal<object>(PyType_Type.tp_alloc(&PyType_Type, 0));
-        auto type = (PyHeapTypeObject*) type_holder.ptr();
-
-        if (!type_holder || !name)
-            pybind11_fail(std::string(rec->name) + ": Unable to create type object!");
 
         /* Register supplemental type information in C++ dict */
-        detail::type_info *tinfo = new detail::type_info();
+        auto *tinfo = new detail::type_info();
-        tinfo->type = (PyTypeObject *) type;
+        tinfo->type = (PyTypeObject *) m_ptr;
-        tinfo->type_size = rec->type_size;
+        tinfo->type_size = rec.type_size;
-        tinfo->init_holder = rec->init_holder;
+        tinfo->init_holder = rec.init_holder;
+        tinfo->dealloc = rec.dealloc;
+
+        auto &internals = get_internals();
+        auto tindex = std::type_index(*rec.type);
         tinfo->direct_conversions = &internals.direct_conversions[tindex];
-        tinfo->default_holder = rec->default_holder;
+        tinfo->default_holder = rec.default_holder;
         internals.registered_types_cpp[tindex] = tinfo;
-        internals.registered_types_py[type] = tinfo;
+        internals.registered_types_py[m_ptr] = tinfo;
 
-        /* Basic type attributes */
+        if (rec.bases.size() > 1 || rec.multiple_inheritance)
-        type->ht_type.tp_name = strdup(full_name.c_str());
+            mark_parents_nonsimple(tinfo->type);
-        type->ht_type.tp_basicsize = (ssize_t) rec->instance_size;
-
-        if (num_bases > 0) {
-            type->ht_type.tp_base = (PyTypeObject *) ((object) bases[0]).inc_ref().ptr();
-            type->ht_type.tp_bases = bases.release().ptr();
-            rec->multiple_inheritance |= num_bases > 1;
-        }
-
-        type->ht_name = name.release().ptr();
-
-#if PY_MAJOR_VERSION >= 3 && PY_MINOR_VERSION >= 3
-        type->ht_qualname = ht_qualname.release().ptr();
-#endif
-
-        /* Custom metaclass if requested (used for static properties) */
-        if (rec->metaclass)
-            PYBIND11_OB_TYPE(type->ht_type) = internals.default_metaclass;
-
-        /* Supported protocols */
-        type->ht_type.tp_as_number = &type->as_number;
-        type->ht_type.tp_as_sequence = &type->as_sequence;
-        type->ht_type.tp_as_mapping = &type->as_mapping;
-
-        /* Supported elementary operations */
-        type->ht_type.tp_init = (initproc) init;
-        type->ht_type.tp_new = (newfunc) new_instance;
-        type->ht_type.tp_dealloc = rec->dealloc;
-
-        /* Support weak references (needed for the keep_alive feature) */
-        type->ht_type.tp_weaklistoffset = offsetof(instance_essentials<void>, weakrefs);
-
-        /* Flags */
-        type->ht_type.tp_flags |= Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HEAPTYPE;
-#if PY_MAJOR_VERSION < 3
-        type->ht_type.tp_flags |= Py_TPFLAGS_CHECKTYPES;
-#endif
-        type->ht_type.tp_flags &= ~Py_TPFLAGS_HAVE_GC;
-
-        /* Support dynamic attributes */
-        if (rec->dynamic_attr) {
-            #if defined(PYPY_VERSION)
-                pybind11_fail(std::string(rec->name) + ": dynamic attributes are "
-                                                       "currently not supported in "
-                                                       "conunction with PyPy!");
-            #endif
-            type->ht_type.tp_flags |= Py_TPFLAGS_HAVE_GC;
-            type->ht_type.tp_dictoffset = type->ht_type.tp_basicsize; // place the dict at the end
-            type->ht_type.tp_basicsize += sizeof(PyObject *); // and allocate enough space for it
-            type->ht_type.tp_getset = generic_getset;
-            type->ht_type.tp_traverse = traverse;
-            type->ht_type.tp_clear = clear;
-        }
-
-        if (rec->buffer_protocol) {
-            type->ht_type.tp_as_buffer = &type->as_buffer;
-#if PY_MAJOR_VERSION < 3
-            type->ht_type.tp_flags |= Py_TPFLAGS_HAVE_NEWBUFFER;
-#endif
-            type->as_buffer.bf_getbuffer = getbuffer;
-            type->as_buffer.bf_releasebuffer = releasebuffer;
-        }
-
-        type->ht_type.tp_doc = tp_doc;
-
-        m_ptr = type_holder.ptr();
-
-        if (PyType_Ready(&type->ht_type) < 0)
-            pybind11_fail(std::string(rec->name) + ": PyType_Ready failed (" +
-                          detail::error_string() + ")!");
-
-        if (scope_module) // Needed by pydoc
-            attr("__module__") = scope_module;
-
-        /* Register type with the parent scope */
-        if (rec->scope)
-            rec->scope.attr(handle(type->ht_name)) = *this;
-
-        if (rec->multiple_inheritance)
-            mark_parents_nonsimple(&type->ht_type);
-
-        type_holder.release();
     }
 
     /// Helper function which tags all parents of a type using mult. inheritance
@@ -963,66 +806,6 @@ protected:
         }
     }
 
-    static int init(void *self, PyObject *, PyObject *) {
-        PyTypeObject *type = Py_TYPE(self);
-        std::string msg;
-#if defined(PYPY_VERSION)
-        msg += handle((PyObject *) type).attr("__module__").cast<std::string>() + ".";
-#endif
-        msg += type->tp_name;
-        msg += ": No constructor defined!";
-        PyErr_SetString(PyExc_TypeError, msg.c_str());
-        return -1;
-    }
-
-    static PyObject *new_instance(PyTypeObject *type, PyObject *, PyObject *) {
-        instance<void> *self = (instance<void> *) PyType_GenericAlloc((PyTypeObject *) type, 0);
-        auto tinfo = detail::get_type_info(type);
-        self->value = ::operator new(tinfo->type_size);
-        self->owned = true;
-        self->holder_constructed = false;
-        detail::get_internals().registered_instances.emplace(self->value, (PyObject *) self);
-        return (PyObject *) self;
-    }
-
-    static void dealloc(instance<void> *self) {
-        if (self->value) {
-            auto instance_type = Py_TYPE(self);
-            auto &registered_instances = detail::get_internals().registered_instances;
-            auto range = registered_instances.equal_range(self->value);
-            bool found = false;
-            for (auto it = range.first; it != range.second; ++it) {
-                if (instance_type == Py_TYPE(it->second)) {
-                    registered_instances.erase(it);
-                    found = true;
-                    break;
-                }
-            }
-            if (!found)
-                pybind11_fail("generic_type::dealloc(): Tried to deallocate unregistered instance!");
-
-            if (self->weakrefs)
-                PyObject_ClearWeakRefs((PyObject *) self);
-
-            PyObject **dict_ptr = _PyObject_GetDictPtr((PyObject *) self);
-            if (dict_ptr)
-                Py_CLEAR(*dict_ptr);
-        }
-        Py_TYPE(self)->tp_free((PyObject*) self);
-    }
-
-    static int traverse(PyObject *op, visitproc visit, void *arg) {
-        PyObject *&dict = *_PyObject_GetDictPtr(op);
-        Py_VISIT(dict);
-        return 0;
-    }
-
-    static int clear(PyObject *op) {
-        PyObject *&dict = *_PyObject_GetDictPtr(op);
-        Py_CLEAR(dict);
-        return 0;
-    }
-
     void install_buffer_funcs(
             buffer_info *(*get_buffer)(PyObject *, void *),
             void *get_buffer_data) {
@@ -1040,37 +823,6 @@ protected:
         tinfo->get_buffer_data = get_buffer_data;
     }
 
-    static int getbuffer(PyObject *obj, Py_buffer *view, int flags) {
-        auto tinfo = detail::get_type_info(Py_TYPE(obj));
-        if (view == nullptr || obj == nullptr || !tinfo || !tinfo->get_buffer) {
-            if (view)
-                view->obj = nullptr;
-            PyErr_SetString(PyExc_BufferError, "generic_type::getbuffer(): Internal error");
-            return -1;
-        }
-        memset(view, 0, sizeof(Py_buffer));
-        buffer_info *info = tinfo->get_buffer(obj, tinfo->get_buffer_data);
-        view->obj = obj;
-        view->ndim = 1;
-        view->internal = info;
-        view->buf = info->ptr;
-        view->itemsize = (ssize_t) info->itemsize;
-        view->len = view->itemsize;
-        for (auto s : info->shape)
-            view->len *= s;
-        if ((flags & PyBUF_FORMAT) == PyBUF_FORMAT)
-            view->format = const_cast<char *>(info->format.c_str());
-        if ((flags & PyBUF_STRIDES) == PyBUF_STRIDES) {
-            view->ndim = (int) info->ndim;
-            view->strides = (ssize_t *) &info->strides[0];
-            view->shape = (ssize_t *) &info->shape[0];
-        }
-        Py_INCREF(view->obj);
-        return 0;
-    }
-
-    static void releasebuffer(PyObject *, Py_buffer *view) { delete (buffer_info *) view->internal; }
-
     void def_property_static_impl(const char *name,
                                   handle fget, handle fset,
                                   detail::function_record *rec_fget) {
@@ -1078,7 +830,7 @@ protected:
         const auto has_doc = rec_fget->doc && pybind11::options::show_user_defined_docstrings();
 
         if (is_static) {
-            auto mclass = handle((PyObject *) PYBIND11_OB_TYPE(*((PyTypeObject *) m_ptr)));
+            auto mclass = handle((PyObject *) Py_TYPE(m_ptr));
 
             if ((PyTypeObject *) mclass.ptr() == &PyType_Type)
                 pybind11_fail(
@@ -1140,7 +892,7 @@ public:
         /* Process optional arguments, if any */
         detail::process_attributes<Extra...>::init(extra..., &record);
 
-        detail::generic_type::initialize(&record);
+        detail::generic_type::initialize(record);
 
         if (has_alias) {
             auto &instances = pybind11::detail::get_internals().registered_types_cpp;
@@ -1352,8 +1104,6 @@ private:
             inst->holder.~holder_type();
         else if (inst->owned)
             ::operator delete(inst->value);
-
-        generic_type::dealloc((detail::instance<void> *) inst);
     }
 
     static detail::function_record *get_function_record(handle h) {

tests/test_inheritance.cpp

@@ -36,6 +36,10 @@ public:
     Hamster(const std::string &name) : Pet(name, "rodent") {}
 };
 
+class Chimera : public Pet {
+    Chimera() : Pet("Kimmy", "chimera") {}
+};
+
 std::string pet_name_species(const Pet &pet) {
     return pet.name() + " is a " + pet.species();
 }
@@ -74,6 +78,8 @@ test_initializer inheritance([](py::module &m) {
     py::class_<Hamster, Pet>(m, "Hamster")
         .def(py::init<std::string>());
 
+    py::class_<Chimera, Pet>(m, "Chimera");
+
     m.def("pet_name_species", pet_name_species);
     m.def("dog_bark", dog_bark);
 

tests/test_inheritance.py

@@ -2,7 +2,7 @@ import pytest
 
 
 def test_inheritance(msg):
-    from pybind11_tests import Pet, Dog, Rabbit, Hamster, dog_bark, pet_name_species
+    from pybind11_tests import Pet, Dog, Rabbit, Hamster, Chimera, dog_bark, pet_name_species
 
     roger = Rabbit('Rabbit')
     assert roger.name() + " is a " + roger.species() == "Rabbit is a parrot"
@@ -30,6 +30,10 @@ def test_inheritance(msg):
         Invoked with: <m.Pet object at 0>
     """
 
+    with pytest.raises(TypeError) as excinfo:
+        Chimera("lion", "goat")
+    assert "No constructor defined!" in str(excinfo.value)
+
 
 def test_automatic_upcasting():
     from pybind11_tests import return_class_1, return_class_2, return_class_n, return_none

tests/test_multiple_inheritance.cpp

@@ -81,3 +81,73 @@ test_initializer multiple_inheritance_nonexplicit([](py::module &m) {
     m.def("bar_base2a", [](Base2a *b) { return b->bar(); });
     m.def("bar_base2a_sharedptr", [](std::shared_ptr<Base2a> b) { return b->bar(); });
 });
+
+struct Vanilla {
+    std::string vanilla() { return "Vanilla"; };
+};
+
+struct WithStatic1 {
+    static std::string static_func1() { return "WithStatic1"; };
+    static int static_value1;
+};
+
+struct WithStatic2 {
+    static std::string static_func2() { return "WithStatic2"; };
+    static int static_value2;
+};
+
+struct WithDict { };
+
+struct VanillaStaticMix1 : Vanilla, WithStatic1, WithStatic2 {
+    static std::string static_func() { return "VanillaStaticMix1"; }
+    static int static_value;
+};
+
+struct VanillaStaticMix2 : WithStatic1, Vanilla, WithStatic2 {
+    static std::string static_func() { return "VanillaStaticMix2"; }
+    static int static_value;
+};
+
+struct VanillaDictMix1 : Vanilla, WithDict { };
+struct VanillaDictMix2 : WithDict, Vanilla { };
+
+int WithStatic1::static_value1 = 1;
+int WithStatic2::static_value2 = 2;
+int VanillaStaticMix1::static_value = 12;
+int VanillaStaticMix2::static_value = 12;
+
+test_initializer mi_static_properties([](py::module &pm) {
+    auto m = pm.def_submodule("mi");
+
+    py::class_<Vanilla>(m, "Vanilla")
+        .def(py::init<>())
+        .def("vanilla", &Vanilla::vanilla);
+
+    py::class_<WithStatic1>(m, "WithStatic1", py::metaclass())
+        .def(py::init<>())
+        .def_static("static_func1", &WithStatic1::static_func1)
+        .def_readwrite_static("static_value1", &WithStatic1::static_value1);
+
+    py::class_<WithStatic2>(m, "WithStatic2", py::metaclass())
+        .def(py::init<>())
+        .def_static("static_func2", &WithStatic2::static_func2)
+        .def_readwrite_static("static_value2", &WithStatic2::static_value2);
+
+    py::class_<VanillaStaticMix1, Vanilla, WithStatic1, WithStatic2>(
+        m, "VanillaStaticMix1", py::metaclass())
+        .def(py::init<>())
+        .def_static("static_func", &VanillaStaticMix1::static_func)
+        .def_readwrite_static("static_value", &VanillaStaticMix1::static_value);
+
+    py::class_<VanillaStaticMix2, WithStatic1, Vanilla, WithStatic2>(
+        m, "VanillaStaticMix2", py::metaclass())
+        .def(py::init<>())
+        .def_static("static_func", &VanillaStaticMix2::static_func)
+        .def_readwrite_static("static_value", &VanillaStaticMix2::static_value);
+
+#if !defined(PYPY_VERSION)
+    py::class_<WithDict>(m, "WithDict", py::dynamic_attr()).def(py::init<>());
+    py::class_<VanillaDictMix1, Vanilla, WithDict>(m, "VanillaDictMix1").def(py::init<>());
+    py::class_<VanillaDictMix2, WithDict, Vanilla>(m, "VanillaDictMix2").def(py::init<>());
+#endif
+});

tests/test_multiple_inheritance.py

@@ -1,3 +1,6 @@
+import pytest
+
+
 def test_multiple_inheritance_cpp():
     from pybind11_tests import MIType
 
@@ -49,6 +52,17 @@ def test_multiple_inheritance_mix2():
     assert mt.bar() == 4
 
 
+def test_multiple_inheritance_error():
+    """Inheriting from multiple C++ bases in Python is not supported"""
+    from pybind11_tests import Base1, Base2
+
+    with pytest.raises(TypeError) as excinfo:
+        # noinspection PyUnusedLocal
+        class MI(Base1, Base2):
+            pass
+    assert "Can't inherit from multiple C++ classes in Python" in str(excinfo.value)
+
+
 def test_multiple_inheritance_virtbase():
     from pybind11_tests import Base12a, bar_base2a, bar_base2a_sharedptr
 
@@ -60,3 +74,38 @@ def test_multiple_inheritance_virtbase():
     assert mt.bar() == 4
     assert bar_base2a(mt) == 4
     assert bar_base2a_sharedptr(mt) == 4
+
+
+def test_mi_static_properties():
+    """Mixing bases with and without static properties should be possible
+     and the result should be independent of base definition order"""
+    from pybind11_tests import mi
+
+    for d in (mi.VanillaStaticMix1(), mi.VanillaStaticMix2()):
+        assert d.vanilla() == "Vanilla"
+        assert d.static_func1() == "WithStatic1"
+        assert d.static_func2() == "WithStatic2"
+        assert d.static_func() == d.__class__.__name__
+
+        mi.WithStatic1.static_value1 = 1
+        mi.WithStatic2.static_value2 = 2
+        assert d.static_value1 == 1
+        assert d.static_value2 == 2
+        assert d.static_value == 12
+
+        d.static_value1 = 0
+        assert d.static_value1 == 0
+        d.static_value2 = 0
+        assert d.static_value2 == 0
+        d.static_value = 0
+        assert d.static_value == 0
+
+
+@pytest.unsupported_on_pypy
+def test_mi_dynamic_attributes():
+    """Mixing bases with and without dynamic attribute support"""
+    from pybind11_tests import mi
+
+    for d in (mi.VanillaDictMix1(), mi.VanillaDictMix2()):
+        d.dynamic = 1
+        assert d.dynamic == 1