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bpo-43224: Draft implementation of PEP 646 #30398

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64abc0a
PEP 646: Grammar and compiler changes
mrahtz Dec 3, 2021
b725671
PEP 646: Add tests for syntax changes
mrahtz Jan 3, 2022
ea329b9
PEP 646: Add AST tests for *args annotations
mrahtz Dec 7, 2021
681dc4e
PEP 646: Add AST tests for return types with unpacking
mrahtz Dec 7, 2021
69f575f
PEP 646: Add AST tests for variable annotations with unpacking
mrahtz Dec 7, 2021
095a620
PEP 646: Add support for starring tuple types
mrahtz Jan 2, 2022
6713748
PEP 646: Add tests for starring tuple types
mrahtz Jan 2, 2022
038b8f0
PEP 646: Implement support in typing.py
mrahtz Jan 2, 2022
f028339
PEP 646: Add tests for everything in typing.py
mrahtz Jan 2, 2022
38c17d3
PEP 646: Add tests for typing.get_{origin,args}
mrahtz Jan 4, 2022
9991937
PEP 646: Various fixes to genericaliasobject.c
mrahtz Jan 15, 2022
9017d22
PEP 646: Fix test_pep646_syntax import
mrahtz Jan 15, 2022
07ed599
PEP 646: Add docstring for TypeVarTuple
mrahtz Jan 17, 2022
74e5252
PEP 646: Swap a Py_INCREF with a Py_NewRef
mrahtz Jan 20, 2022
6cb3aa5
PEP 646: Add test for assigning to a slice containing a star
mrahtz Jan 20, 2022
daef59b
📜🤖 Added by blurb_it.
blurb-it[bot] Jan 20, 2022
3c2a7e7
PEP 646: Add line to Doc/whatsnew
mrahtz Jan 20, 2022
456156a
PEP 646: Use stdbool.h; separate test cases
mrahtz Jan 25, 2022
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PEP 646: Various fixes to genericaliasobject.c 
Based on Fidget-Spinner's feedback:
1. Remove the explicit flag for 'exhausted', instead using 'gi->obj == NULL' to tell whether the iterator is exhausted.
2. Construct `starred_tuple` using the `Py_GenericAlias` constructor instead of constructing it manually.
3. Fix reference counting.
4. Make `Py_GenericAliasIterType` static.
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@mrahtz
mrahtz committed Jan 15, 2022
commit 9991937e5472a9d98868d1426bff09578a4b0c0f
30 changes: 7 additions & 23 deletions Objects/genericaliasobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,6 @@ typedef struct {
typedef struct {
PyObject_HEAD
PyObject *obj; /* Set to NULL when iterator is exhausted */
int exhausted;
} gaiterobject;

static void
Expand Down Expand Up @@ -642,37 +641,23 @@ static PyNumberMethods ga_as_number = {

static PyObject *
ga_iternext(gaiterobject *gi) {
gaobject *alias = (gaobject *) gi->obj;

if (gi->exhausted) {
gi->obj = NULL;
if (gi->obj == NULL) {
return NULL;

@Fidget-Spinner Fidget-Spinner Jan 10, 2022

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I feel like you could potentially be missing a decref here for gi->obj since I see it being increfed in gi_iter. If so,

Suggested change
return NULL;
Py_SETREF(gi->obj, NULL);
return NULL;

If I'm just shooting my mouth off, then just please ignore what I said :).

One way to test for refleaks is to run the tests with the refleak hunter (requires a debug build):

python_d.exe -m test test_typing -R 3:3

@mrahtz mrahtz Jan 15, 2022

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Oh, super nice about the refleak hunter - I had no idea that was a thing!

And good catch about the decref too. One thing I'm unsure about is where we should do it, though. Reading https://docs.python.org/3/c-api/gcsupport.html, am I right in thinking that the iterator object gi counts as a container type, because it contains references to another object? If so, that same page says "Before fields which refer to other containers are invalidated, PyObject_GC_UnTrack() must be called". That would imply we should be setting gi->obj to NULL in the deallocator, in which case we'd also call the setref there?

@mrahtz mrahtz Jan 25, 2022

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Friendly poke :)

}
gi->exhausted = 1;

gaobject *starred_tuple = PyObject_GC_New(gaobject, &Py_GenericAliasType);
starred_tuple->origin = alias->origin;
starred_tuple->args = alias->args;
starred_tuple->parameters = alias->parameters;
starred_tuple->weakreflist = alias->weakreflist;
starred_tuple->starred = 1;
Py_INCREF(alias->args);
// We may not have any parameters to deal with - e.g. `*tuple[int]`
if (alias->parameters != NULL) {
Py_INCREF(alias->parameters);
}
_PyObject_GC_TRACK(starred_tuple);
return (PyObject *) starred_tuple;
gaobject *alias = (gaobject *) gi->obj;
PyObject *starred_tuple = Py_GenericAlias(alias->origin, alias->args);
((gaobject * ) starred_tuple)->starred = 1;
Py_SETREF(gi->obj, NULL);
return starred_tuple;
}

static void
ga_iter_dealloc(gaiterobject *gi) {
_PyObject_GC_UNTRACK(gi);
Py_XDECREF(gi->obj);
PyObject_GC_Del(gi);
}

PyTypeObject Py_GenericAliasIterType = {
static PyTypeObject Py_GenericAliasIterType = {
PyVarObject_HEAD_INIT(&PyType_Type, 0)
.tp_name = "generic_alias_iter",
.tp_basicsize = sizeof(gaiterobject),
Expand All @@ -693,7 +678,6 @@ ga_iter(PyObject *self) {
if (gi == NULL)
return NULL;
gi->obj = self;
gi->exhausted = 0;
Py_INCREF(self);
_PyObject_GC_TRACK(gi);
return (PyObject *) gi;
Expand Down