I think letsencrypt client needs python 2.7 at least if @schoen can confirm
For myself, i have my own Centmin Mod LEMP web stack which can install 3rd party YUM repos for missing packages. One of those is for Rackspace backed IUS Community YUM repo https://iuscommunity.org/pages/Repos.html which supports RHEL/CentOS 5, 6, 7 and has python 2.7, 3.2, 3.3, 3.4 available as side packages which don’t interfere with existing default OS python versions.
Once IUS Community YUM repo is installed you can install Python 2.7 via yum
We’ve been discussing whether or not to continue support for Python 2.6, but in the current development tree we do still officially have Python 2.6 support. So as you found, if there are compatibility problems with CentOS 6, they’re probably a result of another problem.
Hi. I have many sites running on CentOS 6.7 and Drupal. I got letsencrypt working with cron in a non-disruptive way. I created a script and instructions here: https://github.com/mfgering/letsencrypt-lw