[Python-Dev] Arbitrary attributes on funcs and methods

[bwarsaw@python.org]

> Below is a very raw set of patches to add an attribute dictionary to
> funcs and methods.  It's only been minimally tested, but if y'all like
> the idea,

>>>>> "GS" == Greg Stein <gstein@lyra.org> writes:

    GS> +1 on concept, -1 on the patch :-)

Well, that's good, because I /knew/ the patch was a quick hack (which
is why I posted it to python-dev and not patches :).  Since there's
been generally positive feedback on the idea, I think I'll flesh it
out a bit.

    GS> And note that the getattro/setattro is preferred. It is easy
    GS> to extract the char* from them; the other direction requires
    GS> construction of an object.

Good point.

>...
> + 	rtn = PyMember_Get((char *)im, instancemethod_memberlist, name);
> + 	if (rtn == NULL) {
> + 		PyErr_Clear();
> + 		rtn = PyObject_GetAttrString(im->im_func, name);
> + 		if (rtn == NULL)
> + 			PyErr_SetString(PyExc_AttributeError, name);

    GS> Why do you mask this second error with the AttributeError?
    GS> Seems that you should just leave whatever is there (typically
    GS> an AttributeError, but maybe not!).

Good point here, but...

> + 	rtn = PyMember_Get((char *)op, func_memberlist, name);
> + 	if (rtn == NULL) {
> + 		PyErr_Clear();
> + 		rtn = PyDict_GetItemString(op->func_dict, name);
> + 		if (rtn == NULL)
> + 			PyErr_SetString(PyExc_AttributeError, name);

    GS> Again, with the masking...

...here I don't want the KeyError to leak through the getattr() call.
If you do "print func.non_existent_attr" wouldn't you want an
AttributeError instead of a KeyError?  Maybe it should explicitly test
for KeyError rather than masking any error coming back from
PyDict_GetItemString()?  Or better yet (based on your suggestion
below), it should do a PyMapping_HasKey() test, raise an
AttributeError if not, then just return PyMapping_GetItemString().

>...
> + 	else if (strcmp(name, "func_dict") == 0) {
> + 		if (value == NULL || !PyDict_Check(value)) {
> + 			PyErr_SetString(
> + 				PyExc_TypeError,
> + 				"func_dict must be set to a dict object");

    GS> This raises an interesting thought. Why not just require the
    GS> mapping protocol?

Good point again.

-Barry