I use z3c.rml inside a Plone Installation (buildout based 6.1-latest)
I upgrade z3c.rml from 4.5 to Version 5.0 and run the buildout and restart my Plone instance. I get an error on startup:
ModuleNotFoundError: No module named 'z3c.rml'
Is there an explicit import in a zcml file needed? the startup with version 4.5 runs without errors.
The Zope maintainers have just yesterday finished updating packages in the z3c namespace to use native namespace packages instead of pkg_resources namespace packages.
The two kinds are not compatible, so you need to make sure that all packages in the z3c namespace use a version with the same kind. (At least, you do if the packages are installed into different folders, like buildout does.) So, you need to either pin z3c.rml to an older version, or update all the other z3c.* packages to a newer version.
Or, you might be able to use horse-with-no-namespace ยท PyPI which tries to make the different kinds of namespace packages compatible. Note that you cannot install horse-with-no-namespace using buildout, but must pip install it into the same virtualenv where buildout is installed.
NOTE: I see the same for other add-ons also. ( collective.collectionfilter).
This happened to an existing (developing site). Pinning versions to what I had in 6.0 did not work (so for now, my workaround is to 'auto-check it out'.