SCons 3+ supports Python 3.5+ After changing Python requirements, everything goes well.
Change Impact: All ports directly use this tool should be updated/fixed. but after this changes build scripts most likely will be compatible with both Python 2.7 and Python 3.5+
Patch for devel/jsoncpp SConstruct file is attached to the issue for this library.
I tested devel/scons on python 3.7 for a period of time and it works fine. I've requested an exp-run for scons 3.0.5 update, including relaxed python version. Please follow bug #237122 instead. Thanks!
*** This bug has been marked as a duplicate of bug 237122 ***