def test_tuple_resize(self, space, api):
        w_42 = space.wrap(42)
        ar = lltype.malloc(PyObjectP.TO, 1, flavor='raw')

        py_tuple = api.PyTuple_New(3)
        # inside py_tuple is an array of "PyObject *" items which each hold
        # a reference
        rffi.cast(PyTupleObject, py_tuple).c_ob_item[0] = make_ref(space, w_42)
        ar[0] = py_tuple
        api._PyTuple_Resize(ar, 2)
        w_tuple = from_ref(space, ar[0])
        assert space.int_w(space.len(w_tuple)) == 2
        assert space.int_w(space.getitem(w_tuple, space.wrap(0))) == 42
        api.Py_DecRef(ar[0])

        py_tuple = api.PyTuple_New(3)
        rffi.cast(PyTupleObject, py_tuple).c_ob_item[0] = make_ref(space, w_42)
        ar[0] = py_tuple
        api._PyTuple_Resize(ar, 10)
        w_tuple = from_ref(space, ar[0])
        assert space.int_w(space.len(w_tuple)) == 10
        assert space.int_w(space.getitem(w_tuple, space.wrap(0))) == 42
        api.Py_DecRef(ar[0])

        lltype.free(ar, flavor='raw')

def finish_type_2(space, pto, w_obj):
    """
    Sets up other attributes, when the interpreter type has been created.
    """
    pto.c_tp_mro = make_ref(space, space.newtuple(w_obj.mro_w))
    base = pto.c_tp_base
    if base:
        inherit_special(space, pto, base)
    for w_base in space.fixedview(from_ref(space, pto.c_tp_bases)):
        inherit_slots(space, pto, w_base)

    if not pto.c_tp_setattro:
        from pypy.module.cpyext.object import PyObject_GenericSetAttr
        pto.c_tp_setattro = llhelper(
            PyObject_GenericSetAttr.api_func.functype,
            PyObject_GenericSetAttr.api_func.get_wrapper(space))

    if not pto.c_tp_getattro:
        from pypy.module.cpyext.object import PyObject_GenericGetAttr
        pto.c_tp_getattro = llhelper(
            PyObject_GenericGetAttr.api_func.functype,
            PyObject_GenericGetAttr.api_func.get_wrapper(space))

    if w_obj.is_cpytype():
        Py_DecRef(space, pto.c_tp_dict)
        w_dict = w_obj.getdict(space)
        pto.c_tp_dict = make_ref(space, w_dict)

def frame_attach(space, py_obj, w_obj):
    "Fills a newly allocated PyFrameObject with a frame object"
    frame = space.interp_w(PyFrame, w_obj)
    py_frame = rffi.cast(PyFrameObject, py_obj)
    py_frame.c_f_code = rffi.cast(PyCodeObject, make_ref(space, frame.pycode))
    py_frame.c_f_globals = make_ref(space, frame.w_globals)
    rffi.setintfield(py_frame, 'c_f_lineno', frame.f_lineno)

def PyErr_GetExcInfo(space, ptype, pvalue, ptraceback):
    """---Cython extension---

    Retrieve the exception info, as known from ``sys.exc_info()``.  This
    refers to an exception that was already caught, not to an exception
    that was freshly raised.  Returns new references for the three
    objects, any of which may be *NULL*.  Does not modify the exception
    info state.

    .. note::

       This function is not normally used by code that wants to handle
       exceptions.  Rather, it can be used when code needs to save and
       restore the exception state temporarily.  Use
       :c:func:`PyErr_SetExcInfo` to restore or clear the exception
       state.
    """
    ec = space.getexecutioncontext()
    operror = ec.sys_exc_info()
    if operror:
        ptype[0] = make_ref(space, operror.w_type)
        pvalue[0] = make_ref(space, operror.get_w_value(space))
        ptraceback[0] = make_ref(space, space.wrap(operror.get_traceback()))
    else:
        ptype[0] = lltype.nullptr(PyObject.TO)
        pvalue[0] = lltype.nullptr(PyObject.TO)
        ptraceback[0] = lltype.nullptr(PyObject.TO)

    def test_setitem(self, space, api):
        py_tuple = api.PyTuple_New(2)
        api.PyTuple_SetItem(py_tuple, 0, make_ref(space, space.wrap(42)))
        api.PyTuple_SetItem(py_tuple, 1, make_ref(space, space.wrap(43)))

        w_tuple = from_ref(space, py_tuple)
        assert space.eq_w(w_tuple, space.newtuple([space.wrap(42),
                                                   space.wrap(43)]))

def PyFrame_New(space, tstate, w_code, w_globals, w_locals):
    typedescr = get_typedescr(PyFrame.typedef)
    py_obj = typedescr.allocate(space, space.gettypeobject(PyFrame.typedef))
    py_frame = rffi.cast(PyFrameObject, py_obj)
    space.interp_w(PyCode, w_code) # sanity check
    py_frame.c_f_code = rffi.cast(PyCodeObject, make_ref(space, w_code))
    py_frame.c_f_globals = make_ref(space, w_globals)
    return py_frame

def type_attach(space, py_obj, w_type):
    """
    Fills a newly allocated PyTypeObject from an existing type.
    """
    from pypy.module.cpyext.object import PyObject_Del

    assert isinstance(w_type, W_TypeObject)

    pto = rffi.cast(PyTypeObjectPtr, py_obj)

    typedescr = get_typedescr(w_type.layout.typedef)

    # dealloc
    pto.c_tp_dealloc = typedescr.get_dealloc(space)
    # buffer protocol
    if space.is_w(w_type, space.w_str):
        setup_string_buffer_procs(space, pto)
    if space.is_w(w_type, space.w_buffer):
        setup_buffer_buffer_procs(space, pto)

    pto.c_tp_free = llhelper(PyObject_Del.api_func.functype,
            PyObject_Del.api_func.get_wrapper(space))
    pto.c_tp_alloc = llhelper(PyType_GenericAlloc.api_func.functype,
            PyType_GenericAlloc.api_func.get_wrapper(space))
    if pto.c_tp_flags & Py_TPFLAGS_HEAPTYPE:
        w_typename = space.getattr(w_type, space.wrap('__name__'))
        heaptype = rffi.cast(PyHeapTypeObject, pto)
        heaptype.c_ht_name = make_ref(space, w_typename)
        from pypy.module.cpyext.bytesobject import PyString_AsString
        pto.c_tp_name = PyString_AsString(space, heaptype.c_ht_name)
    else:
        pto.c_tp_name = rffi.str2charp(w_type.name)
    # uninitialized fields:
    # c_tp_print, c_tp_getattr, c_tp_setattr
    # XXX implement
    # c_tp_compare and the following fields (see http://docs.python.org/c-api/typeobj.html )
    w_base = best_base(space, w_type.bases_w)
    pto.c_tp_base = rffi.cast(PyTypeObjectPtr, make_ref(space, w_base))

    builder = space.fromcache(StaticObjectBuilder)
    if builder.cpyext_type_init is not None:
        builder.cpyext_type_init.append((pto, w_type))
    else:
        finish_type_1(space, pto)
        finish_type_2(space, pto, w_type)

    pto.c_tp_basicsize = rffi.sizeof(typedescr.basestruct)
    if pto.c_tp_base:
        if pto.c_tp_base.c_tp_basicsize > pto.c_tp_basicsize:
            pto.c_tp_basicsize = pto.c_tp_base.c_tp_basicsize

    # will be filled later on with the correct value
    # may not be 0
    if space.is_w(w_type, space.w_object):
        pto.c_tp_new = rffi.cast(newfunc, 1)
    update_all_slots(space, w_type, pto)
    pto.c_tp_flags |= Py_TPFLAGS_READY
    return pto

def slice_attach(space, py_obj, w_obj):
    """
    Fills a newly allocated PySliceObject with the given slice object. The
    fields must not be modified.
    """
    py_slice = rffi.cast(PySliceObject, py_obj)
    assert isinstance(w_obj, W_SliceObject)
    py_slice.c_start = make_ref(space, w_obj.w_start)
    py_slice.c_stop = make_ref(space, w_obj.w_stop)
    py_slice.c_step = make_ref(space, w_obj.w_step)

def traceback_attach(space, py_obj, w_obj):
    py_traceback = rffi.cast(PyTracebackObject, py_obj)
    traceback = space.interp_w(PyTraceback, w_obj)
    if traceback.next is None:
        w_next_traceback = None
    else:
        w_next_traceback = space.wrap(traceback.next)
    py_traceback.c_tb_next = rffi.cast(PyTracebackObject, make_ref(space, w_next_traceback))
    py_traceback.c_tb_frame = rffi.cast(PyFrameObject, make_ref(space, space.wrap(traceback.frame)))
    rffi.setintfield(py_traceback, 'c_tb_lasti', traceback.lasti)
    rffi.setintfield(py_traceback, 'c_tb_lineno',traceback.get_lineno())

def code_attach(space, py_obj, w_obj):
    py_code = rffi.cast(PyCodeObject, py_obj)
    assert isinstance(w_obj, PyCode)
    py_code.c_co_name = make_ref(space, space.wrap(w_obj.co_name))
    py_code.c_co_filename = make_ref(space, space.wrap(w_obj.co_filename))
    co_flags = 0
    for name, value in ALL_CODE_FLAGS:
        if w_obj.co_flags & getattr(pycode, name):
            co_flags |= value
    rffi.setintfield(py_code, 'c_co_flags', co_flags)
    rffi.setintfield(py_code, 'c_co_argcount', w_obj.co_argcount)

def PyErr_NormalizeException(space, exc_p, val_p, tb_p):
    """Under certain circumstances, the values returned by PyErr_Fetch() below
    can be "unnormalized", meaning that *exc is a class object but *val is
    not an instance of the  same class.  This function can be used to instantiate
    the class in that case.  If the values are already normalized, nothing happens.
    The delayed normalization is implemented to improve performance."""
    operr = OperationError(from_ref(space, exc_p[0]),
                           from_ref(space, val_p[0]))
    operr.normalize_exception(space)
    Py_DecRef(space, exc_p[0])
    Py_DecRef(space, val_p[0])
    exc_p[0] = make_ref(space, operr.w_type)
    val_p[0] = make_ref(space, operr.get_w_value(space))

 def test_ConcatAndDel(self, space, api):
     ref1 = make_ref(space, space.wrap('abc'))
     ref2 = make_ref(space, space.wrap('def'))
     ptr = lltype.malloc(PyObjectP.TO, 1, flavor='raw')
     ptr[0] = ref1
     api.PyString_ConcatAndDel(ptr, ref2)
     assert space.str_w(from_ref(space, ptr[0])) == 'abcdef'
     assert ref2.c_ob_refcnt == 0
     Py_DecRef(space, ptr[0])
     ptr[0] = lltype.nullptr(PyObject.TO)
     ref2 = make_ref(space, space.wrap('foo'))
     api.PyString_ConcatAndDel(ptr, ref2) # should not crash
     assert ref2.c_ob_refcnt == 0
     lltype.free(ptr, flavor='raw')

def PyList_SET_ITEM(space, w_list, index, w_item):
    """Macro form of PyList_SetItem() without error checking. This is normally
    only used to fill in new lists where there is no previous content.

    This function "steals" a reference to item, and, unlike PyList_SetItem(),
    does not discard a reference to any item that it being replaced; any
    reference in list at position i will be leaked.
    """
    assert isinstance(w_list, W_ListObject)
    assert 0 <= index < w_list.length()
    # Deliberately leak, so that it can be safely decref'd.
    make_ref(space, w_list.getitem(index))
    Py_DecRef(space, w_item)
    w_list.setitem(index, w_item)
    return w_item

def PyObject_GetBuffer(space, w_obj, view, flags):
    """Export obj into a Py_buffer, view.  These arguments must
    never be NULL.  The flags argument is a bit field indicating what
    kind of buffer the caller is prepared to deal with and therefore what
    kind of buffer the exporter is allowed to return.  The buffer interface
    allows for complicated memory sharing possibilities, but some caller may
    not be able to handle all the complexity but may want to see if the
    exporter will let them take a simpler view to its memory.

    Some exporters may not be able to share memory in every possible way and
    may need to raise errors to signal to some consumers that something is
    just not possible. These errors should be a BufferError unless
    there is another error that is actually causing the problem. The
    exporter can use flags information to simplify how much of the
    Py_buffer structure is filled in with non-default values and/or
    raise an error if the object can't support a simpler view of its memory.

    0 is returned on success and -1 on error."""
    flags = widen(flags)
    buf = space.buffer_w(w_obj, flags)
    try:
        view.c_buf = rffi.cast(rffi.VOIDP, buf.get_raw_address())
    except ValueError:
        raise BufferError("could not create buffer from object")
    ret = fill_Py_buffer(space, buf, view)
    view.c_obj = make_ref(space, w_obj)
    return ret

 def convert_argument_libffi(self, space, w_obj, argchain, call_local):
     if hasattr(space, "fake"):
         raise NotImplementedError
     space.getbuiltinmodule("cpyext")
     from pypy.module.cpyext.pyobject import make_ref
     ref = make_ref(space, w_obj)
     argchain.arg(rffi.cast(rffi.VOIDP, ref))

def _PyTuple_Resize(space, ref, newsize):
    """Can be used to resize a tuple.  newsize will be the new length of the tuple.
    Because tuples are supposed to be immutable, this should only be used if there
    is only one reference to the object.  Do not use this if the tuple may already
    be known to some other part of the code.  The tuple will always grow or shrink
    at the end.  Think of this as destroying the old tuple and creating a new one,
    only more efficiently.  Returns 0 on success. Client code should never
    assume that the resulting value of *p will be the same as before calling
    this function. If the object referenced by *p is replaced, the original
    *p is destroyed.  On failure, returns -1 and sets *p to NULL, and
    raises MemoryError or SystemError."""
    py_tuple = from_ref(space, ref[0])
    if not PyTuple_Check(space, py_tuple):
        PyErr_BadInternalCall(space)
    py_newtuple = PyTuple_New(space, newsize)
    
    to_cp = newsize
    oldsize = space.int_w(space.len(py_tuple))
    if oldsize < newsize:
        to_cp = oldsize
    for i in range(to_cp):
        _setitem_tuple(py_newtuple, i, space.getitem(py_tuple, space.wrap(i)))
    Py_DecRef(space, ref[0])
    ref[0] = make_ref(space, py_newtuple)
    return 0

def bytes_getbuffer(space, w_str, view, flags):
    from pypy.module.cpyext.bytesobject import PyBytes_AsString

    view.c_obj = make_ref(space, w_str)
    view.c_buf = rffi.cast(rffi.VOIDP, PyBytes_AsString(space, view.c_obj))
    view.c_len = space.len_w(w_str)
    return 0

    def test_iterkeys(self, space, api):
        w_dict = space.sys.getdict(space)
        py_dict = make_ref(space, w_dict)

        ppos = lltype.malloc(Py_ssize_tP.TO, 1, flavor='raw')
        pkey = lltype.malloc(PyObjectP.TO, 1, flavor='raw')
        pvalue = lltype.malloc(PyObjectP.TO, 1, flavor='raw')

        keys_w = []
        values_w = []
        try:
            ppos[0] = 0
            while api.PyDict_Next(w_dict, ppos, pkey, None):
                w_key = from_ref(space, pkey[0])
                keys_w.append(w_key)
            ppos[0] = 0
            while api.PyDict_Next(w_dict, ppos, None, pvalue):
                w_value = from_ref(space, pvalue[0])
                values_w.append(w_value)
        finally:
            lltype.free(ppos, flavor='raw')
            lltype.free(pkey, flavor='raw')
            lltype.free(pvalue, flavor='raw')

        api.Py_DecRef(py_dict) # release borrowed references

        assert space.eq_w(space.newlist(keys_w),
                          space.call_method(w_dict, "keys"))
        assert space.eq_w(space.newlist(values_w),
                          space.call_method(w_dict, "values"))

def PyByteArray_FromObject(space, w_obj):
    """Return a new bytearray object from any object, o, that implements the
    buffer protocol.

    XXX expand about the buffer protocol, at least somewhere"""
    w_buffer = space.call_function(space.w_bytearray, w_obj)
    return make_ref(space, w_buffer)

def buffer_attach(space, py_obj, w_obj):
    """
    Fills a newly allocated PyBufferObject with the given (str) buffer object.
    """
    py_buf = rffi.cast(PyBufferObject, py_obj)
    py_buf.c_b_offset = 0
    rffi.setintfield(py_buf, 'c_b_readonly', 1)
    rffi.setintfield(py_buf, 'c_b_hash', -1)

    if isinstance(w_obj, SubBuffer):
        py_buf.c_b_offset = w_obj.offset
        w_obj = w_obj.buffer

    # If w_obj already allocated a fixed buffer, use it, and keep a
    # reference to w_obj.
    # Otherwise, b_base stays NULL, and we own the b_ptr.

    if isinstance(w_obj, StringBuffer):
        py_buf.c_b_base = lltype.nullptr(PyObject.TO)
        py_buf.c_b_ptr = rffi.cast(rffi.VOIDP, rffi.str2charp(w_obj.value))
        py_buf.c_b_size = w_obj.getlength()
    elif isinstance(w_obj, ArrayBuffer):
        w_base = w_obj.array
        py_buf.c_b_base = make_ref(space, w_base)
        py_buf.c_b_ptr = rffi.cast(rffi.VOIDP, w_obj.array._charbuf_start())
        py_buf.c_b_size = w_obj.getlength()
    else:
        raise OperationError(space.w_NotImplementedError, space.wrap(
            "buffer flavor not supported"))