Incorrect error message for vectors

[Starbuck5]

I was digging through the math.c source and found this:

>>> import pygame
pygame-ce 2.5.2.dev1 (SDL 2.30.6, Python 3.9.5)
>>> a = pygame.Vector2(30,40)
>>> del a.y
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: Cannot delete the x attribute

I didn't try to delete the x attribute, I tried to delete the y attribute!

Implementation code (unchanged for 8 years):

static int
vector_set_component(pgVector *self, PyObject *value, int component)
{
    if (value == NULL) {
        PyErr_SetString(PyExc_TypeError, "Cannot delete the x attribute");
        return -1;
    }
    if (component >= self->dim) {
        PyErr_BadInternalCall();
        return -1;
    }

    self->coords[component] = PyFloat_AsDouble(value);
    if (PyErr_Occurred())
        return -1;
    return 0;
}

[damusss]

This is probably related to the CPython API (but finding an answer online is hard because google doesn't understand the difference between python and cpython), but why is the function for setting the component also handling deletion?

[aatle]

Hmm, so vector x, y, z, and w all call vector_set_component from their setter function, which only has one hard-coded error message.

Also I am no C or CPython expert, but why is there seemingly unused w coordinate stuff in the code?

---

@damusss I did a bit of research and found the relevant C-API stuff:

pygame Vector2 properties:

pygame-ce/src_c/math.c

Lines 2605 to 2609 in 3183d16

	static PyGetSetDef vector2_getsets[] = {
	{"x", (getter)vector_getx, (setter)vector_setx, NULL, NULL},
	{"y", (getter)vector_gety, (setter)vector_sety, NULL, NULL},
	{NULL, 0, NULL, NULL, NULL} /* Sentinel */
	};

PyGetSetDef docs state:

setter set
Optional C function to set or delete the attribute. If NULL, the attribute is read-only.

[oddbookworm]

Also I am no C or CPython expert, but why is there seemingly unused w coordinate stuff in the code?

Because it looks like someone at some point started implementing a Vector4 class, which doesn't fully exist

why is the function for setting the component also handling deletion?

https://docs.python.org/3/c-api/object.html#c.PyObject_SetAttr
Because that's a special-case for it, but it's deprecated behavior. I suggest moving to PyObject_DelAttr or PyObject_DelAttrString (which are both stable ABI as of 3.13 and both exist in all of our supported python versions)

[oddbookworm]

In fact, looks like it might emit an error in the future as we have it python/cpython#106572 (comment)

[Starbuck5]

It handles deletion because that’s how the Python C API works.

This is not about pyobject_setattr.

[oddbookworm]

It handles deletion because that’s how the Python C API works.

This is not about pyobject_setattr.

It actually is. The docs and that cpython comment indicate that the behavior is deprecated and you shouldn't have PyObject_SetAttr do your deleting anymore

[oddbookworm]

Hold on, I'm dumb

[damusss]

Thanks @aatle and @Starbuck5 for the info :)