CC-ing Chris in case he is not subscribed to bugs by default.
I have attempted to update src:python-prov to the latest upstream release which depends on rdflib. I added python{,3}-rdflib to the list of b-deps and ran the build.
The build FTBFS due to a failed query on html5lib at test time. Since the prov module does not explicitly depend on the latter, it had to be missing transitively from rdflib.
Upon inspection of the packaging repository, I noticed that html5lib is listed as recommends and that automatic dependency resolution via dh-python is explicitly disabled.
This is a bad idea and should be replaced straight away by ${python:Depends} and ${python3:Depends}, plus a normal call to dh_python{,3}. Python packages rarely need recommends, since modules either have strict install dependencies (install_requires), going in the substitution variable, or optional ones (extra_require), going in Suggests.
Cheers, Ghis
