Taken from daily iso build 20140312 live session:
elementary@elementary:~$ software-properties-gtk
Traceback (most recent call last):
File "/usr/bin/software-properties-gtk", line 101, in <module>
app = SoftwarePropertiesGtk(datadir=options.data_dir, options=options, file=file)
File "/usr/lib/python3/dist-packages/softwareproperties/gtk/SoftwarePropertiesGtk.py", line 98, in __init__
SoftwareProperties.__init__(self, options=options, datadir=datadir)
File "/usr/lib/python3/dist-packages/softwareproperties/SoftwareProperties.py", line 109, in __init__
self.reload_sourceslist()
File "/usr/lib/python3/dist-packages/softwareproperties/SoftwareProperties.py", line 599, in reload_sourceslist
self.distro.get_sources(self.sourceslist)
File "/usr/lib/python3/dist-packages/aptsources/distro.py", line 89, in get_sources
(self.id, self.codename))
aptsources.distro.NoDistroTemplateException: Error: could not find a distribution template for elementary OS/isis
Looks like we'll have to port our Luna patch to Isis, both to python-apt and python3-apt. That should fix it.