This function is called from only one place. Maybe there are special
conditions that the one call site already ensures?
I tried to see if there are situations where obj==NULL arises, and there
are. I'm a little unclear on where -- I've narrowed down one case to any
class inheriting from Protocol, so that makes me wonder if
`__init_subclass__` is involved.
On Fri, Aug 14, 2020 at 9:52 AM Skip Montanaro <skip.montan...@gmail.com>
wrote:
> (I'm far from certain this is the correct place for this message. Maybe I
> should have opened a case on bpo instead?)
>
> I got far behind on my register instruction set stuff and in the interim
> the ground shifted underneath me. I'm still working to try and get the test
> suite to pass (modulo test_ssl, which I expect to fail on Ubuntu 20.04 for
> the time being).
>
> In trying to track down where my code differs from the main/3.10 branch, I
> was looking at the super_init_without_args() function in typeobject.c.
> I'm puzzled by this chunk of code near the top:
>
> PyObject *obj = f->f_localsplus[0];
> Py_ssize_t i, n;
> if (obj == NULL && co->co_cell2arg) {
> /* The first argument might be a cell. */
> n = PyTuple_GET_SIZE(co->co_cellvars);
> for (i = 0; i < n; i++) {
> if (co->co_cell2arg[i] == 0) {
> PyObject *cell = f->f_localsplus[co->co_nlocals + i];
> assert(PyCell_Check(cell));
> obj = PyCell_GET(cell);
> break;
> }
> }
> }
>
> More specifically, the test for f->f_localsplus[0] being NULL seems odd.
> I can understand that there might not be any local variables, but there is
> no test for co->co_nlocals == 0. Since we don't know how many locals
> there might be, if there were none, wouldn't a reference to a cell variable
> or free variable occupy the first slot (assuming there are any)? I guess
> I'm confused about what the obj == NULL term in the if statement's
> expression is doing for us.
>
> On a (maybe not) related note, there is a comment further down in
> super_init():
>
> /* Call super(), without args -- fill in from __class__
> and first local variable on the stack. */
>
> I'm not seeing where the first local variable on the stack is used to fill
> anything in, certainly not within the block guarded by the type == NULL
> expression.
>
> Skip
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--
--Guido van Rossum (python.org/~guido)
*Pronouns: he/him **(why is my pronoun here?)*
<http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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