Graceful no DistRDF

[ellert]

This Pull request:

Missing experimental add-on module ROOT.RDF.Experimental.Distributed (DistRDF) should not fail the loading of the rest of the ROOT.RDF namespace.

Also addresses a mismatch in the minimum Python version check in the code vs. cmake.

Checklist:

• tested changes locally
• updated the docs (if necessary)

This PR fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2173518

[phsft-bot]

Starting build on ROOT-debian10-i386/soversion, ROOT-performance-centos8-multicore/cxx17, ROOT-ubuntu18.04/nortcxxmod, ROOT-ubuntu2004/python3, mac12/noimt, mac11/cxx14, windows10/cxx14
How to customize builds

[phsft-bot]

Build failed on ROOT-ubuntu2004/python3.
Running on root-ubuntu-2004-1.cern.ch:/home/sftnight/build/workspace/root-pullrequests-build
See console output.

Failing tests:

• projectroot.roottest.root.hist.roottest_root_hist_h2root

[vepadulano]

Thanks @ellert ! Although I'm curious about what scenario reproduced your error. AFAIK given a ROOT build with Python 3.8, RDataFrame and PyROOT active, the DistRDF module is always available. Maybe the error was triggered by the wrong if sys.version_info >= (3, 7) in your build? I saw your comments on the linked bug report, all clear, thanks again for catching this!

[ellert]

This is an RPM packaged root. It is split into several packages in order to be flexible so that users can install the parts they need. So someone who installs the pyroot package does not necessarily install also the distrdf package, so it can be missing in their user installation. They should still be able to use the non-distrdf part of ROOT.RDF namespace.