New submission from STINNER Victor:
Currently, PyTypeObject fields are set in order in the C code. Typical example:
PyTypeObject PyMethod_Type = {
PyVarObject_HEAD_INIT(&PyType_Type, 0)
"method",
sizeof(PyMethodObject),
0,
(destructor)method_dealloc, /* tp_dealloc */
0, /* tp_print */
0, /* tp_getattr */
0, /* tp_setattr */
0, /* tp_reserved */
(reprfunc)method_repr, /* tp_repr */
0, /* tp_as_number */
0, /* tp_as_sequence */
0, /* tp_as_mapping */
(hashfunc)method_hash, /* tp_hash */
method_call, /* tp_call */
0, /* tp_str */
method_getattro, /* tp_getattro */
PyObject_GenericSetAttr, /* tp_setattro */
0, /* tp_as_buffer */
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC, /* tp_flags */
method_doc, /* tp_doc */
(traverseproc)method_traverse, /* tp_traverse */
0, /* tp_clear */
method_richcompare, /* tp_richcompare */
offsetof(PyMethodObject, im_weakreflist), /* tp_weaklistoffset */
0, /* tp_iter */
0, /* tp_iternext */
method_methods, /* tp_methods */
method_memberlist, /* tp_members */
method_getset, /* tp_getset */
0, /* tp_base */
0, /* tp_dict */
method_descr_get, /* tp_descr_get */
0, /* tp_descr_set */
0, /* tp_dictoffset */
0, /* tp_init */
0, /* tp_alloc */
method_new, /* tp_new */
};
The aligned comment is an old practice required to be able to see to which
field correspond a line.
This syntax usually produces a lot of zeros.
The C standard (C99?) allows to use a more readable syntax:
PyTypeObject PyMethod_Type = {
PyVarObject_HEAD_INIT(&PyType_Type, 0)
.tp_name = "method",
.tp_basicsize = sizeof(PyMethodObject),
.tp_dealloc = (destructor)method_dealloc,
.tp_repr = (reprfunc)method_repr,
.tp_hash = (hashfunc)method_hash,
.tp_call = method_call,
.tp_getattro = method_getattro,
...
};
It seems like it's possible to start with positional fields and then switch to
named fields, so PyVarObject_HEAD_INIT() still works. Maybe maybe
PyVarObject_HEAD_INIT() should also evolve? Or maybe we need a new macro using
the ".tp_xxx=...," syntax?
INADA Naoki proposed to use this syntax in my pull request which adds a new
tp_fastcall field which requires to add many zeros:
https://github.com/python/cpython/pull/65#pullrequestreview-16566423
Example of change:
@@ -370,6 +370,17 @@ PyTypeObject PyMethod_Type = {
0, /* tp_init */
0, /* tp_alloc */
method_new, /* tp_new */
+ 0, /* tp_free */
+ 0, /* tp_is_gc */
+ 0, /* tp_bases */
+ 0, /* tp_mro */
+ 0, /* tp_cache */
+ 0, /* tp_subclasses */
+ 0, /* tp_weaklist */
+ 0, /* tp_del */
+ 0, /* tp_version_tag */
+ 0, /* tp_finalize */
+ (fastternaryfunc)method_fastcall, /* tp_fastcall */
};
----------
messages: 285399
nosy: haypo, inada.naoki
priority: normal
severity: normal
status: open
title: Use designated initializers to define PyTypeObject types
versions: Python 3.7
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue29260>
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