The problem here is not one with gnome-keyring specifically but with the python script
/opt/local/bin/gtk-builder-convert
which is provided by port gtk2.
gtk-builder-convert starts with
#!/usr/bin/env python
which should be patched/reinplaced (in gtk2) to directly specify a particular safe python binary.
Most current gtk/gnome ports use python25 although a few gnome ports (alacarte, gnome-menus) now require python26. So using python25 as the currently most prevalently used python port
#!/usr/bin/env ${prefix)/bin/python2.5
where ${prefix} of course is replaced by the installed MacPorts prefix
This will make the choice of python for the script independent of the current python selection.