install anaconda python 2.7 and 3.6

                                    As suggested here, with an installation of the last anaconda you can create an environment just like Cleb explained or downgrade python :

conda install python=3.6.0
With this second solution, you may encounter some incompatibility issues with other packages. I tested it myself and did not encounter any issue but I guess it depends on the packages you installed.

If you don't want to handle environments or face incompatibilities issues, you can download any Anaconda version here: https://repo.continuum.io/archive/. For example, Anaconda3-5.1.0-XXX or Anaconda3-5.2.0-XXX provides python 3.6 (the suffix XXX depends on your OS).

To know which python is provided in an anaconda package, you can visit the Release notes page. It provides the updates for the all anaconda versions. Find yours and look for the line

python A.B.C -> X.Y.Z

where A.B.C is the previous version and X.Y.Z is the updated python version.

                                    conda create --name py27python=2.7
conda create --name py36 python=3.6