getattr hack not failing graciously on descriptors / tab completion broken in emacs

[nthiery]

The getattr hack of #7921 to let extension types "inherit" from category does not fail graciously on descriptors.

Visible effect: tab completion is broken under emacs:

   sage: n=1
   sage: n.<tab>  # gives nothing

This is a variant of #8223. Emacs does not use dir straight away, but instead calls _ip.IP.magic_psearch which is conservative and does not trust dir. So it actually tries to get all advertised attributes, and in particular the descriptor __weakref__ which failed on 1 and confused getattr.

The attached patch makes the getattr fail graciously in such situations. It probably would be better for __weakref__ to not appear in dir in the first place, but at least this should fix the bug and variants thereof.

Again, better implementations of the getattr hack are most welcome. See comments in the code.

CC: @sagetrac-sage-combinat

Component: misc

Keywords: tab completion, dir, getattr

Author: Nicolas M. Thiéry

Reviewer: Mike Hansen

Merged: sage-4.3.4.alpha1

Issue created by migration from https://trac.sagemath.org/ticket/8296

[nthiery]

Attachment: trac_8296-fix-tab-completion-emacs-nt.patch.gz

[mwhansen]

comment:5

Looks good to me.

[mwhansen]

Reviewer: Mike Hansen

[mwhansen]

Merged: sage-4.3.4.alpha1