Starting build on ROOT-debian10-i386/cxx14, ROOT-performance-centos8-multicore/default, ROOT-fedora32/noimt, ROOT-ubuntu16/nortcxxmod, mac1014/python3, mac11.0/cxx17, windows10/cxx14
How to customize builds

Build failed on ROOT-fedora32/noimt.
Running on root-fedora32-1.cern.ch:/home/sftnight/build/workspace/root-pullrequests-build
See console output.

Warnings:

• [2021-05-27T07:28:56.649Z] math/unuran/unuran-1.8.0-root/src/methods/mvtdr_init.ch:886:17: warning: argument 1 value ‘18446744073709551608’ exceeds maximum object size 9223372036854775807 [-Walloc-size-larger-than=]

Failing tests:

• projectroot.roottest.root.io.uniquePointer.roottest_root_io_uniquePointer_simpleWriteRead
• projectroot.roottest.root.io.uniquePointer.roottest_root_io_uniquePointer_simpleRead
• projectroot.roottest.root.meta.ROOT-7462.roottest_root_meta_ROOT_7462_make

LGTM! Why some of the changes of the upstream patch rather than all of them (if relevant for the future, might be nice to add that info to the commit message)

Thanks! There's some changes in that patch that are not strictly related to Python3.9, and also I added more changes needed for our PyROOT / TPython files - at least it will stay written here!

Test failures are unrelated to these changes, merging.