This actually turns out to be a bug in pybuild (dh-python).
In zope.interface's d/control file we have:
Build-Depends: debhelper (>= 9),
dh-python,
dpkg-dev (>= 1.16.1~),
libpython-all-dbg,
libpython-all-dev,
libpython3-all-dbg,
libpython3-all-dev,
python-all-dbg:any,
python-all-dev:any,
python-setuptools,
python-zope.event,
python3-all-dbg:any,
python3-all-dev:any,
python3-setuptools,
python3-zope.event
Note the ':any' specifier on the interpreter packages. pybuild didn't
recognize these.
I reported this to Piotr who fixed it in dh-python git, which I tested and
verified fixes the problem, so I reassigned this bug to that package.
