GeezerVison is showing github.com — Remove check for float subclasses with nb_float == NULL in PyNumber_Float() ? · Issue #112636 · python/cpython
Remove check for float subclasses with nb_float == NULL in PyNumber_Float() ? #112636DescriptionSimilar check for int subclasses without nb_int was removed in 31a6554 from PyNumber_Long().
// transformed to a separate issue per @serhiy-storchaka suggestion in #112145
Linked PRs
Activityserhiy-storchaka commented on Mar 22, 2024 I still not sure what is more correct. Should we remove the check for float subclasses without nb_float? Did I make a mistake when I deleted the check for int subclasses without nb_int? Both cases are pretty hypothetical now, but we can't change the code without reason, and I don't remember my reasoning.
cc @mdickinson skirpichev commented on Mar 23, 2024 Simple question: when it could be NULL? Clearly, this won't work for simple static types with tp_base set to PyFloat_Type (or it's subtype). Multiple inheritance? serhiy-storchaka commented on Mar 26, 2024 You can create a float subclass in C and explicitly set nb_float to NULL. skirpichev commented on May 14, 2024
You can create a float subclass in C and explicitly set nb_float to NULL
@serhiy-storchaka, I think in this way we could break anything:)
Here is a minimal example, when nb_float == NULL condition could be triggered. (Let me know if you had in mind something simpler.) Should we support such scenario? I doubt.
Subclass code:
static PyNumberMethods xxx_as_number = {
.nb_float = NULL, /* nb_float will be inherited anyway */
};
static PyObject*
fun(PyObject *o, PyObject *Py_UNUSED(ignored))
{
PyNumberMethods *m = Py_TYPE(o)->tp_as_number;
m->nb_float = NULL;
Py_RETURN_NONE;
}
static PyMethodDef xxx_methods[] = {
{"break_it", (PyCFunction) fun, METH_NOARGS, NULL},
{NULL},
};
PyTypeObject XXX_Type = {
PyVarObject_HEAD_INIT(NULL, 0)
.tp_name = "xxx",
.tp_basicsize = sizeof(PyFloatObject),
.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
.tp_base = &PyFloat_Type,
.tp_as_number = &xxx_as_number,
.tp_methods = xxx_methods,
};Session example:
>>> a = xxx(3.14)
>>> float(a) # nb_float == NULL is not triggered, due to inheritance
3.14
>>> a.break_it()
>>> float(a) # and only NOW this branch will work...
XXX
3.14 Edit: pr description was updated with this example. skirpichev commented on Nov 2, 2024 @serhiy-storchaka, I'm closing issue as well. Let me know if we should add a test for this.
PS: As noted in the pr #112637 (comment), the integer workaround shouldn't be restored.
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