Thanks for the report.  After looking into this a bit, the URLs you are using are those from the daily docs build, the latest doc changes checked into each branch.  As best I can tell, the part of the daily build that makes the downloadable files has been broken, probably for some time and most likely due to trying to use an older version of TeX Live.  Until we can get the server upgraded, you can download the docs that reflect the source as of the 3.6.2 release.  You can find these linked to on the docs download page:

https://www.python.org/doc/versions/

I've reopened the original pythondotorg issue since it turns out to be a server issue.