I'd strongly suggest you contact the maintainer of the python3 package and request a backport. 3.5.1 is in testing, so it should be possible, and perhaps even easy to backport.
Tbh it might be as easy as recompiling it, Debian makes it very easy to recompile stuff, dpkg-buildpackage is trivial to run. Do it once on a throwaway image, keep the resulting package(s) forever - until new official ones land. This sort of approach can be a risk in production environments but for development images is fine and dandy.
toyg|9 years ago