SCons release 3.1.1 now available from the download page at SourceForge. This release should be used instead of 3.1.0. This release fixes several issues. This release supports Python versions 2.7.* as well as 3.5+. You can view ChangeLog

Note that due to many changes needed to support both 2.7 and 3.5+ switching python between 2.7 and 3.5+ will cause rebuilds of some targets.