typeobject.c

/* Type object implementation */

#include "Python.h"
#include "frameobject.h"
#include "structmember.h"

#include <ctype.h>

/*[clinic input]
class type "PyTypeObject *" "&PyType_Type"
class object "PyObject *" "&PyBaseObject_Type"
[clinic start generated code]*/
/*[clinic end generated code: output=da39a3ee5e6b4b0d input=4b94608d231c434b]*/

#include "clinic/typeobject.c.h"

/* Support type attribute cache */

/* The cache can keep references to the names alive for longer than
   they normally would.  This is why the maximum size is limited to
   MCACHE_MAX_ATTR_SIZE, since it might be a problem if very large
   strings are used as attribute names. */
#define MCACHE_MAX_ATTR_SIZE    100
#define MCACHE_SIZE_EXP         12
#define MCACHE_HASH(version, name_hash)                                 \
        (((unsigned int)(version) ^ (unsigned int)(name_hash))          \
         & ((1 << MCACHE_SIZE_EXP) - 1))

#define MCACHE_HASH_METHOD(type, name)                                  \
        MCACHE_HASH((type)->tp_version_tag,                     \
                    ((PyASCIIObject *)(name))->hash)
#define MCACHE_CACHEABLE_NAME(name)                                     \
        PyUnicode_CheckExact(name) &&                            \
        PyUnicode_READY(name) != -1 &&                      \
        PyUnicode_GET_LENGTH(name) <= MCACHE_MAX_ATTR_SIZE

struct method_cache_entry {
    unsigned int version;
    PyObject *name;             /* reference to exactly a str or None */
    PyObject *value;            /* borrowed */
};

static struct method_cache_entry method_cache[1 << MCACHE_SIZE_EXP];
static unsigned int next_version_tag = 0;

#define MCACHE_STATS 0

#if MCACHE_STATS
static size_t method_cache_hits = 0;
static size_t method_cache_misses = 0;
static size_t method_cache_collisions = 0;
#endif

/* alphabetical order */
_Py_IDENTIFIER(__abstractmethods__);
_Py_IDENTIFIER(__class__);
_Py_IDENTIFIER(__delitem__);
_Py_IDENTIFIER(__dict__);
_Py_IDENTIFIER(__doc__);
_Py_IDENTIFIER(__getattribute__);
_Py_IDENTIFIER(__getitem__);
_Py_IDENTIFIER(__hash__);
_Py_IDENTIFIER(__init_subclass__);
_Py_IDENTIFIER(__len__);
_Py_IDENTIFIER(__module__);
_Py_IDENTIFIER(__name__);
_Py_IDENTIFIER(__new__);
_Py_IDENTIFIER(__set_name__);
_Py_IDENTIFIER(__setitem__);
_Py_IDENTIFIER(builtins);

static PyObject *
slot_tp_new(PyTypeObject *type, PyObject *args, PyObject *kwds);

static void
clear_slotdefs(void);

/*
 * finds the beginning of the docstring's introspection signature.
 * if present, returns a pointer pointing to the first '('.
 * otherwise returns NULL.
 *
 * doesn't guarantee that the signature is valid, only that it
 * has a valid prefix.  (the signature must also pass skip_signature.)
 */
static const char *
find_signature(const char *name, const char *doc)
{
    const char *dot;
    size_t length;

    if (!doc)
        return NULL;

    assert(name != NULL);

    /* for dotted names like classes, only use the last component */
    dot = strrchr(name, '.');
    if (dot)
        name = dot + 1;

    length = strlen(name);
    if (strncmp(doc, name, length))
        return NULL;
    doc += length;
    if (*doc != '(')
        return NULL;
    return doc;
}

#define SIGNATURE_END_MARKER         ")\n--\n\n"
#define SIGNATURE_END_MARKER_LENGTH  6
/*
 * skips past the end of the docstring's instrospection signature.
 * (assumes doc starts with a valid signature prefix.)
 */
static const char *
skip_signature(const char *doc)
{
    while (*doc) {
        if ((*doc == *SIGNATURE_END_MARKER) &&
            !strncmp(doc, SIGNATURE_END_MARKER, SIGNATURE_END_MARKER_LENGTH))
            return doc + SIGNATURE_END_MARKER_LENGTH;
        if ((*doc == '\n') && (doc[1] == '\n'))
            return NULL;
        doc++;
    }
    return NULL;
}

#ifndef NDEBUG
static int
_PyType_CheckConsistency(PyTypeObject *type)
{
    if (!(type->tp_flags & Py_TPFLAGS_READY)) {
        /* don't check types before PyType_Ready() */
        return 1;
    }

    assert(!(type->tp_flags & Py_TPFLAGS_READYING));
    assert(type->tp_mro != NULL && PyTuple_Check(type->tp_mro));
    assert(type->tp_dict != NULL);
    return 1;
}
#endif

static const char *
_PyType_DocWithoutSignature(const char *name, const char *internal_doc)
{
    const char *doc = find_signature(name, internal_doc);

    if (doc) {
        doc = skip_signature(doc);
        if (doc)
            return doc;
        }
    return internal_doc;
}

PyObject *
_PyType_GetDocFromInternalDoc(const char *name, const char *internal_doc)
{
    const char *doc = _PyType_DocWithoutSignature(name, internal_doc);

    if (!doc || *doc == '\0') {
        Py_RETURN_NONE;
    }

    return PyUnicode_FromString(doc);
}

PyObject *
_PyType_GetTextSignatureFromInternalDoc(const char *name, const char *internal_doc)
{
    const char *start = find_signature(name, internal_doc);
    const char *end;

    if (start)
        end = skip_signature(start);
    else
        end = NULL;
    if (!end) {
        Py_RETURN_NONE;
    }

    /* back "end" up until it points just past the final ')' */
    end -= SIGNATURE_END_MARKER_LENGTH - 1;
    assert((end - start) >= 2); /* should be "()" at least */
    assert(end[-1] == ')');
    assert(end[0] == '\n');
    return PyUnicode_FromStringAndSize(start, end - start);
}

unsigned int
PyType_ClearCache(void)
{
    Py_ssize_t i;
    unsigned int cur_version_tag = next_version_tag - 1;

#if MCACHE_STATS
    size_t total = method_cache_hits + method_cache_collisions + method_cache_misses;
    fprintf(stderr, "-- Method cache hits        = %zd (%d%%)\n",
            method_cache_hits, (int) (100.0 * method_cache_hits / total));
    fprintf(stderr, "-- Method cache true misses = %zd (%d%%)\n",
            method_cache_misses, (int) (100.0 * method_cache_misses / total));
    fprintf(stderr, "-- Method cache collisions  = %zd (%d%%)\n",
            method_cache_collisions, (int) (100.0 * method_cache_collisions / total));
    fprintf(stderr, "-- Method cache size        = %zd KB\n",
            sizeof(method_cache) / 1024);
#endif

    for (i = 0; i < (1 << MCACHE_SIZE_EXP); i++) {
        method_cache[i].version = 0;
        Py_CLEAR(method_cache[i].name);
        method_cache[i].value = NULL;
    }
    next_version_tag = 0;
    /* mark all version tags as invalid */
    PyType_Modified(&PyBaseObject_Type);
    return cur_version_tag;
}

void
_PyType_Fini(void)
{
    PyType_ClearCache();
    clear_slotdefs();
}

void
PyType_Modified(PyTypeObject *type)
{
    /* Invalidate any cached data for the specified type and all
       subclasses.  This function is called after the base
       classes, mro, or attributes of the type are altered.

       Invariants:

       - Py_TPFLAGS_VALID_VERSION_TAG is never set if
         Py_TPFLAGS_HAVE_VERSION_TAG is not set (e.g. on type
         objects coming from non-recompiled extension modules)

       - before Py_TPFLAGS_VALID_VERSION_TAG can be set on a type,
         it must first be set on all super types.

       This function clears the Py_TPFLAGS_VALID_VERSION_TAG of a
       type (so it must first clear it on all subclasses).  The
       tp_version_tag value is meaningless unless this flag is set.
       We don't assign new version tags eagerly, but only as
       needed.
     */
    PyObject *raw, *ref;
    Py_ssize_t i;

    if (!PyType_HasFeature(type, Py_TPFLAGS_VALID_VERSION_TAG))
        return;

    raw = type->tp_subclasses;
    if (raw != NULL) {
        assert(PyDict_CheckExact(raw));
        i = 0;
        while (PyDict_Next(raw, &i, NULL, &ref)) {
            assert(PyWeakref_CheckRef(ref));
            ref = PyWeakref_GET_OBJECT(ref);
            if (ref != Py_None) {
                PyType_Modified((PyTypeObject *)ref);
            }
        }
    }
    type->tp_flags &= ~Py_TPFLAGS_VALID_VERSION_TAG;
}

static void
type_mro_modified(PyTypeObject *type, PyObject *bases) {
    /*
       Check that all base classes or elements of the MRO of type are
       able to be cached.  This function is called after the base
       classes or mro of the type are altered.

       Unset HAVE_VERSION_TAG and VALID_VERSION_TAG if the type
       has a custom MRO that includes a type which is not officially
       super type.

       Called from mro_internal, which will subsequently be called on
       each subclass when their mro is recursively updated.
     */
    Py_ssize_t i, n;
    int clear = 0;

    if (!PyType_HasFeature(type, Py_TPFLAGS_HAVE_VERSION_TAG))
        return;

    n = PyTuple_GET_SIZE(bases);
    for (i = 0; i < n; i++) {
        PyObject *b = PyTuple_GET_ITEM(bases, i);
        PyTypeObject *cls;

        assert(PyType_Check(b));
        cls = (PyTypeObject *)b;

        if (!PyType_HasFeature(cls, Py_TPFLAGS_HAVE_VERSION_TAG) ||
            !PyType_IsSubtype(type, cls)) {
            clear = 1;
            break;
        }
    }

    if (clear)
        type->tp_flags &= ~(Py_TPFLAGS_HAVE_VERSION_TAG|
                            Py_TPFLAGS_VALID_VERSION_TAG);
}

static int
assign_version_tag(PyTypeObject *type)
{
    /* Ensure that the tp_version_tag is valid and set
       Py_TPFLAGS_VALID_VERSION_TAG.  To respect the invariant, this
       must first be done on all super classes.  Return 0 if this
       cannot be done, 1 if Py_TPFLAGS_VALID_VERSION_TAG.
    */
    Py_ssize_t i, n;
    PyObject *bases;

    if (PyType_HasFeature(type, Py_TPFLAGS_VALID_VERSION_TAG))
        return 1;
    if (!PyType_HasFeature(type, Py_TPFLAGS_HAVE_VERSION_TAG))
        return 0;
    if (!PyType_HasFeature(type, Py_TPFLAGS_READY))
        return 0;

    type->tp_version_tag = next_version_tag++;
    /* for stress-testing: next_version_tag &= 0xFF; */

    if (type->tp_version_tag == 0) {
        /* wrap-around or just starting Python - clear the whole
           cache by filling names with references to Py_None.
           Values are also set to NULL for added protection, as they
           are borrowed reference */
        for (i = 0; i < (1 << MCACHE_SIZE_EXP); i++) {
            method_cache[i].value = NULL;
            Py_INCREF(Py_None);
            Py_XSETREF(method_cache[i].name, Py_None);
        }
        /* mark all version tags as invalid */
        PyType_Modified(&PyBaseObject_Type);
        return 1;
    }
    bases = type->tp_bases;
    n = PyTuple_GET_SIZE(bases);
    for (i = 0; i < n; i++) {
        PyObject *b = PyTuple_GET_ITEM(bases, i);
        assert(PyType_Check(b));
        if (!assign_version_tag((PyTypeObject *)b))
            return 0;
    }
    type->tp_flags |= Py_TPFLAGS_VALID_VERSION_TAG;
    return 1;
}


static PyMemberDef type_members[] = {
    {"__basicsize__", T_PYSSIZET, offsetof(PyTypeObject,tp_basicsize),READONLY},
    {"__itemsize__", T_PYSSIZET, offsetof(PyTypeObject, tp_itemsize), READONLY},
    {"__flags__", T_LONG, offsetof(PyTypeObject, tp_flags), READONLY},
    {"__weakrefoffset__", T_LONG,
     offsetof(PyTypeObject, tp_weaklistoffset), READONLY},
    {"__base__", T_OBJECT, offsetof(PyTypeObject, tp_base), READONLY},
    {"__dictoffset__", T_LONG,
     offsetof(PyTypeObject, tp_dictoffset), READONLY},
    {"__mro__", T_OBJECT, offsetof(PyTypeObject, tp_mro), READONLY},
    {0}
};

static int
check_set_special_type_attr(PyTypeObject *type, PyObject *value, const char *name)
{
    if (!(type->tp_flags & Py_TPFLAGS_HEAPTYPE)) {
        PyErr_Format(PyExc_TypeError,
                     "can't set %s.%s", type->tp_name, name);
        return 0;
    }
    if (!value) {
        PyErr_Format(PyExc_TypeError,
                     "can't delete %s.%s", type->tp_name, name);
        return 0;
    }
    return 1;
}

static PyObject *
type_name(PyTypeObject *type, void *context)
{
    const char *s;

    if (type->tp_flags & Py_TPFLAGS_HEAPTYPE) {
        PyHeapTypeObject* et = (PyHeapTypeObject*)type;

        Py_INCREF(et->ht_name);
        return et->ht_name;
    }
    else {
        s = strrchr(type->tp_name, '.');
        if (s == NULL)
            s = type->tp_name;
        else
            s++;
        return PyUnicode_FromString(s);
    }
}

static PyObject *
type_qualname(PyTypeObject *type, void *context)
{
    if (type->tp_flags & Py_TPFLAGS_HEAPTYPE) {
        PyHeapTypeObject* et = (PyHeapTypeObject*)type;
        Py_INCREF(et->ht_qualname);
        return et->ht_qualname;
    }
    else {
        return type_name(type, context);
    }
}

static int
type_set_name(PyTypeObject *type, PyObject *value, void *context)
{
    const char *tp_name;
    Py_ssize_t name_size;

    if (!check_set_special_type_attr(type, value, "__name__"))
        return -1;
    if (!PyUnicode_Check(value)) {
        PyErr_Format(PyExc_TypeError,
                     "can only assign string to %s.__name__, not '%s'",
                     type->tp_name, Py_TYPE(value)->tp_name);
        return -1;
    }

    tp_name = PyUnicode_AsUTF8AndSize(value, &name_size);
    if (tp_name == NULL)
        return -1;
    if (strlen(tp_name) != (size_t)name_size) {
        PyErr_SetString(PyExc_ValueError,
                        "type name must not contain null characters");
        return -1;
    }

    type->tp_name = tp_name;
    Py_INCREF(value);
    Py_SETREF(((PyHeapTypeObject*)type)->ht_name, value);

    return 0;
}

static int
type_set_qualname(PyTypeObject *type, PyObject *value, void *context)
{
    PyHeapTypeObject* et;

    if (!check_set_special_type_attr(type, value, "__qualname__"))
        return -1;
    if (!PyUnicode_Check(value)) {
        PyErr_Format(PyExc_TypeError,
                     "can only assign string to %s.__qualname__, not '%s'",
                     type->tp_name, Py_TYPE(value)->tp_name);
        return -1;
    }

    et = (PyHeapTypeObject*)type;
    Py_INCREF(value);
    Py_SETREF(et->ht_qualname, value);
    return 0;
}

static PyObject *
type_module(PyTypeObject *type, void *context)
{
    PyObject *mod;

    if (type->tp_flags & Py_TPFLAGS_HEAPTYPE) {
        mod = _PyDict_GetItemId(type->tp_dict, &PyId___module__);
        if (mod == NULL) {
            PyErr_Format(PyExc_AttributeError, "__module__");
            return NULL;
        }
        Py_INCREF(mod);
    }
    else {
        const char *s = strrchr(type->tp_name, '.');
        if (s != NULL) {
            mod = PyUnicode_FromStringAndSize(
                type->tp_name, (Py_ssize_t)(s - type->tp_name));
            if (mod != NULL)
                PyUnicode_InternInPlace(&mod);
        }
        else {
            mod = _PyUnicode_FromId(&PyId_builtins);
            Py_XINCREF(mod);
        }
    }
    return mod;
}

static int
type_set_module(PyTypeObject *type, PyObject *value, void *context)
{
    if (!check_set_special_type_attr(type, value, "__module__"))
        return -1;

    PyType_Modified(type);

    return _PyDict_SetItemId(type->tp_dict, &PyId___module__, value);
}

static PyObject *
type_abstractmethods(PyTypeObject *type, void *context)
{
    PyObject *mod = NULL;
    /* type itself has an __abstractmethods__ descriptor (this). Don't return
       that. */
    if (type != &PyType_Type)
        mod = _PyDict_GetItemId(type->tp_dict, &PyId___abstractmethods__);
    if (!mod) {
        PyObject *message = _PyUnicode_FromId(&PyId___abstractmethods__);
        if (message)
            PyErr_SetObject(PyExc_AttributeError, message);
        return NULL;
    }
    Py_INCREF(mod);
    return mod;
}

static int
type_set_abstractmethods(PyTypeObject *type, PyObject *value, void *context)
{
    /* __abstractmethods__ should only be set once on a type, in
       abc.ABCMeta.__new__, so this function doesn't do anything
       special to update subclasses.
    */
    int abstract, res;
    if (value != NULL) {
        abstract = PyObject_IsTrue(value);
        if (abstract < 0)
            return -1;
        res = _PyDict_SetItemId(type->tp_dict, &PyId___abstractmethods__, value);
    }
    else {
        abstract = 0;
        res = _PyDict_DelItemId(type->tp_dict, &PyId___abstractmethods__);
        if (res && PyErr_ExceptionMatches(PyExc_KeyError)) {
            PyObject *message = _PyUnicode_FromId(&PyId___abstractmethods__);
            if (message)
                PyErr_SetObject(PyExc_AttributeError, message);
            return -1;
        }
    }
    if (res == 0) {
        PyType_Modified(type);
        if (abstract)
            type->tp_flags |= Py_TPFLAGS_IS_ABSTRACT;
        else
            type->tp_flags &= ~Py_TPFLAGS_IS_ABSTRACT;
    }
    return res;
}

static PyObject *
type_get_bases(PyTypeObject *type, void *context)
{
    Py_INCREF(type->tp_bases);
    return type->tp_bases;
}

static PyTypeObject *best_base(PyObject *);
static int mro_internal(PyTypeObject *, PyObject **);
static int type_is_subtype_base_chain(PyTypeObject *, PyTypeObject *);
static int compatible_for_assignment(PyTypeObject *, PyTypeObject *, const char *);
static int add_subclass(PyTypeObject*, PyTypeObject*);
static int add_all_subclasses(PyTypeObject *type, PyObject *bases);
static void remove_subclass(PyTypeObject *, PyTypeObject *);
static void remove_all_subclasses(PyTypeObject *type, PyObject *bases);
static void update_all_slots(PyTypeObject *);

typedef int (*update_callback)(PyTypeObject *, void *);
static int update_subclasses(PyTypeObject *type, PyObject *name,
                             update_callback callback, void *data);
static int recurse_down_subclasses(PyTypeObject *type, PyObject *name,
                                   update_callback callback, void *data);

static int
mro_hierarchy(PyTypeObject *type, PyObject *temp)
{
    int res;
    PyObject *new_mro, *old_mro;
    PyObject *tuple;
    PyObject *subclasses;
    Py_ssize_t i, n;

    res = mro_internal(type, &old_mro);
    if (res <= 0)
        /* error / reentrance */
        return res;
    new_mro = type->tp_mro;

    if (old_mro != NULL)
        tuple = PyTuple_Pack(3, type, new_mro, old_mro);
    else
        tuple = PyTuple_Pack(2, type, new_mro);

    if (tuple != NULL)
        res = PyList_Append(temp, tuple);
    else
        res = -1;
    Py_XDECREF(tuple);

    if (res < 0) {
        type->tp_mro = old_mro;
        Py_DECREF(new_mro);
        return -1;
    }
    Py_XDECREF(old_mro);

    /* Obtain a copy of subclasses list to iterate over.

       Otherwise type->tp_subclasses might be altered
       in the middle of the loop, for example, through a custom mro(),
       by invoking type_set_bases on some subclass of the type
       which in turn calls remove_subclass/add_subclass on this type.

       Finally, this makes things simple avoiding the need to deal
       with dictionary iterators and weak references.
    */
    subclasses = type___subclasses___impl(type);
    if (subclasses == NULL)
        return -1;
    n = PyList_GET_SIZE(subclasses);
    for (i = 0; i < n; i++) {
        PyTypeObject *subclass;
        subclass = (PyTypeObject *)PyList_GET_ITEM(subclasses, i);
        res = mro_hierarchy(subclass, temp);
        if (res < 0)
            break;
    }
    Py_DECREF(subclasses);

    return res;
}

static int
type_set_bases(PyTypeObject *type, PyObject *new_bases, void *context)
{
    int res = 0;
    PyObject *temp;
    PyObject *old_bases;
    PyTypeObject *new_base, *old_base;
    Py_ssize_t i;

    if (!check_set_special_type_attr(type, new_bases, "__bases__"))
        return -1;
    if (!PyTuple_Check(new_bases)) {
        PyErr_Format(PyExc_TypeError,
             "can only assign tuple to %s.__bases__, not %s",
                 type->tp_name, Py_TYPE(new_bases)->tp_name);
        return -1;
    }
    if (PyTuple_GET_SIZE(new_bases) == 0) {
        PyErr_Format(PyExc_TypeError,
             "can only assign non-empty tuple to %s.__bases__, not ()",
                 type->tp_name);
        return -1;
    }
    for (i = 0; i < PyTuple_GET_SIZE(new_bases); i++) {
        PyObject *ob;
        PyTypeObject *base;

        ob = PyTuple_GET_ITEM(new_bases, i);
        if (!PyType_Check(ob)) {
            PyErr_Format(PyExc_TypeError,
                         "%s.__bases__ must be tuple of classes, not '%s'",
                         type->tp_name, Py_TYPE(ob)->tp_name);
            return -1;
        }

        base = (PyTypeObject*)ob;
        if (PyType_IsSubtype(base, type) ||
            /* In case of reentering here again through a custom mro()
               the above check is not enough since it relies on
               base->tp_mro which would gonna be updated inside
               mro_internal only upon returning from the mro().

               However, base->tp_base has already been assigned (see
               below), which in turn may cause an inheritance cycle
               through tp_base chain.  And this is definitely
               not what you want to ever happen.  */
            (base->tp_mro != NULL && type_is_subtype_base_chain(base, type))) {

            PyErr_SetString(PyExc_TypeError,
                            "a __bases__ item causes an inheritance cycle");
            return -1;
        }
    }

    new_base = best_base(new_bases);
    if (new_base == NULL)
        return -1;

    if (!compatible_for_assignment(type->tp_base, new_base, "__bases__"))
        return -1;

    Py_INCREF(new_bases);
    Py_INCREF(new_base);

    old_bases = type->tp_bases;
    old_base = type->tp_base;

    type->tp_bases = new_bases;
    type->tp_base = new_base;

    temp = PyList_New(0);
    if (temp == NULL)
        goto bail;
    if (mro_hierarchy(type, temp) < 0)
        goto undo;
    Py_DECREF(temp);

    /* Take no action in case if type->tp_bases has been replaced
       through reentrance.  */
    if (type->tp_bases == new_bases) {
        /* any base that was in __bases__ but now isn't, we
           need to remove |type| from its tp_subclasses.
           conversely, any class now in __bases__ that wasn't
           needs to have |type| added to its subclasses. */

        /* for now, sod that: just remove from all old_bases,
           add to all new_bases */
        remove_all_subclasses(type, old_bases);
        res = add_all_subclasses(type, new_bases);
        update_all_slots(type);
    }

    Py_DECREF(old_bases);
    Py_DECREF(old_base);

    assert(_PyType_CheckConsistency(type));
    return res;

  undo:
    for (i = PyList_GET_SIZE(temp) - 1; i >= 0; i--) {
        PyTypeObject *cls;
        PyObject *new_mro, *old_mro = NULL;

        PyArg_UnpackTuple(PyList_GET_ITEM(temp, i),
                          "", 2, 3, &cls, &new_mro, &old_mro);
        /* Do not rollback if cls has a newer version of MRO.  */
        if (cls->tp_mro == new_mro) {
            Py_XINCREF(old_mro);
            cls->tp_mro = old_mro;
            Py_DECREF(new_mro);
        }
    }
    Py_DECREF(temp);

  bail:
    if (type->tp_bases == new_bases) {
        assert(type->tp_base == new_base);

        type->tp_bases = old_bases;
        type->tp_base = old_base;

        Py_DECREF(new_bases);
        Py_DECREF(new_base);
    }
    else {
        Py_DECREF(old_bases);
        Py_DECREF(old_base);
    }

    assert(_PyType_CheckConsistency(type));
    return -1;
}

static PyObject *
type_dict(PyTypeObject *type, void *context)
{
    if (type->tp_dict == NULL) {
        Py_RETURN_NONE;
    }
    return PyDictProxy_New(type->tp_dict);
}

static PyObject *
type_get_doc(PyTypeObject *type, void *context)
{
    PyObject *result;
    if (!(type->tp_flags & Py_TPFLAGS_HEAPTYPE) && type->tp_doc != NULL) {
        return _PyType_GetDocFromInternalDoc(type->tp_name, type->tp_doc);
    }
    result = _PyDict_GetItemId(type->tp_dict, &PyId___doc__);
    if (result == NULL) {
        result = Py_None;
        Py_INCREF(result);
    }
    else if (Py_TYPE(result)->tp_descr_get) {
        result = Py_TYPE(result)->tp_descr_get(result, NULL,
                                               (PyObject *)type);
    }
    else {
        Py_INCREF(result);
    }
    return result;
}

static PyObject *
type_get_text_signature(PyTypeObject *type, void *context)
{
    return _PyType_GetTextSignatureFromInternalDoc(type->tp_name, type->tp_doc);
}

static int
type_set_doc(PyTypeObject *type, PyObject *value, void *context)
{
    if (!check_set_special_type_attr(type, value, "__doc__"))
        return -1;
    PyType_Modified(type);
    return _PyDict_SetItemId(type->tp_dict, &PyId___doc__, value);
}

/*[clinic input]
type.__instancecheck__ -> bool

    instance: object
    /

Check if an object is an instance.
[clinic start generated code]*/

static int
type___instancecheck___impl(PyTypeObject *self, PyObject *instance)
/*[clinic end generated code: output=08b6bf5f591c3618 input=cdbfeaee82c01a0f]*/
{
    return _PyObject_RealIsInstance(instance, (PyObject *)self);
}

/*[clinic input]
type.__subclasscheck__ -> bool

    subclass: object
    /

Check if a class is a subclass.
[clinic start generated code]*/

static int
type___subclasscheck___impl(PyTypeObject *self, PyObject *subclass)
/*[clinic end generated code: output=97a4e51694500941 input=071b2ca9e03355f4]*/
{
    return _PyObject_RealIsSubclass(subclass, (PyObject *)self);
}


static PyGetSetDef type_getsets[] = {
    {"__name__", (getter)type_name, (setter)type_set_name, NULL},
    {"__qualname__", (getter)type_qualname, (setter)type_set_qualname, NULL},
    {"__bases__", (getter)type_get_bases, (setter)type_set_bases, NULL},
    {"__module__", (getter)type_module, (setter)type_set_module, NULL},
    {"__abstractmethods__", (getter)type_abstractmethods,
     (setter)type_set_abstractmethods, NULL},
    {"__dict__",  (getter)type_dict,  NULL, NULL},
    {"__doc__", (getter)type_get_doc, (setter)type_set_doc, NULL},
    {"__text_signature__", (getter)type_get_text_signature, NULL, NULL},
    {0}
};

static PyObject *
type_repr(PyTypeObject *type)
{
    PyObject *mod, *name, *rtn;

    mod = type_module(type, NULL);
    if (mod == NULL)
        PyErr_Clear();
    else if (!PyUnicode_Check(mod)) {
        Py_DECREF(mod);
        mod = NULL;
    }
    name = type_qualname(type, NULL);
    if (name == NULL) {
        Py_XDECREF(mod);
        return NULL;
    }

    if (mod != NULL && !_PyUnicode_EqualToASCIIId(mod, &PyId_builtins))
        rtn = PyUnicode_FromFormat("<class '%U.%U'>", mod, name);
    else
        rtn = PyUnicode_FromFormat("<class '%s'>", type->tp_name);

    Py_XDECREF(mod);
    Py_DECREF(name);
    return rtn;
}

static PyObject *
type_call(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    PyObject *obj;

    if (type->tp_new == NULL) {
        PyErr_Format(PyExc_TypeError,
                     "cannot create '%.100s' instances",
                     type->tp_name);
        return NULL;
    }

#ifdef Py_DEBUG
    /* type_call() must not be called with an exception set,
       because it can clear it (directly or indirectly) and so the
       caller loses its exception */
    assert(!PyErr_Occurred());
#endif

    obj = type->tp_new(type, args, kwds);
    obj = _Py_CheckFunctionResult((PyObject*)type, obj, NULL);
    if (obj == NULL)
        return NULL;

    /* Ugly exception: when the call was type(something),
       don't call tp_init on the result. */
    if (type == &PyType_Type &&
        PyTuple_Check(args) && PyTuple_GET_SIZE(args) == 1 &&
        (kwds == NULL ||
         (PyDict_Check(kwds) && PyDict_GET_SIZE(kwds) == 0)))
        return obj;

    /* If the returned object is not an instance of type,
       it won't be initialized. */
    if (!PyType_IsSubtype(Py_TYPE(obj), type))
        return obj;

    type = Py_TYPE(obj);
    if (type->tp_init != NULL) {
        int res = type->tp_init(obj, args, kwds);
        if (res < 0) {
            assert(PyErr_Occurred());
            Py_DECREF(obj);
            obj = NULL;
        }
        else {
            assert(!PyErr_Occurred());
        }
    }
    return obj;
}

PyObject *
PyType_GenericAlloc(PyTypeObject *type, Py_ssize_t nitems)
{
    PyObject *obj;
    const size_t size = _PyObject_VAR_SIZE(type, nitems+1);
    /* note that we need to add one, for the sentinel */

    if (PyType_IS_GC(type))
        obj = _PyObject_GC_Malloc(size);
    else
        obj = (PyObject *)PyObject_MALLOC(size);

    if (obj == NULL)
        return PyErr_NoMemory();

    memset(obj, '\0', size);

    if (type->tp_flags & Py_TPFLAGS_HEAPTYPE)
        Py_INCREF(type);

    if (type->tp_itemsize == 0)
        (void)PyObject_INIT(obj, type);
    else
        (void) PyObject_INIT_VAR((PyVarObject *)obj, type, nitems);

    if (PyType_IS_GC(type))
        _PyObject_GC_TRACK(obj);
    return obj;
}

PyObject *
PyType_GenericNew(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    return type->tp_alloc(type, 0);
}

/* Helpers for subtyping */

static int
traverse_slots(PyTypeObject *type, PyObject *self, visitproc visit, void *arg)
{
    Py_ssize_t i, n;
    PyMemberDef *mp;

    n = Py_SIZE(type);
    mp = PyHeapType_GET_MEMBERS((PyHeapTypeObject *)type);
    for (i = 0; i < n; i++, mp++) {