There were no new changes
in version 3.5.9; 3.5.9 was released only because of a CDN caching
problem, which resulted in some users downloading a prerelease version
of the 3.5.8 .xz source tarball. Apart from the version number, 3.5.9 is
identical to the proper 3.5.8 release.
You can download Python 3.5.9 here.
Python core development news and information.