The file Python-3.6.0a2.tgz contains paths that start with "..", e.g., 

$ tar tf Python-3.6.0a2.tgz | head
../Python-3.6.0a2/
../Python-3.6.0a2/Doc/
../Python-3.6.0a2/Grammar/
../Python-3.6.0a2/Include/
../Python-3.6.0a2/LICENSE
../Python-3.6.0a2/Lib/
../Python-3.6.0a2/Mac/
../Python-3.6.0a2/Makefile.pre.in
../Python-3.6.0a2/Misc/
../Python-3.6.0a2/Modules/

This causes tar to error out when unpacking the file.

This was not the case in previous tarballs and also not in Python-3.6.0a2.tar.xz.

That's unfortunate and my fault, basically, the .tgz tarball was built with a BSD-ish tar while the .xz one was built with a GNU tar, as intended.  I hate to do a stealth update, unless absolutely necessary, and I don't get see any errors unpacking the .tgz one with a recent GNU tar.  Can you say with which version of tar and on what platform you see the tar failure?  I'll make sure it doesn't happen in subsequent releases.

The affected tar is indeed a BSD-ish tar (OS X).  With GNU tar I can proceed.  It says "gtar: Removing leading `../' from member names".

So with that I agree that it's not worth rerolling this release.

OK, thanks for the info.  I'm going to close this issue as "won't fix" and try real hard not to do it again.

Just as another datapoint: This also breaks installing a2 with pythonz.

In pyenv this was "fixed" by pointing to the .tar.xz archive instead of the .tgz https://github.com/yyuu/pyenv/pull/652, maybe you could implement that for Pythonz?