Some project have strict dependencies, and requires additional python 3.x versions to manage the dependencies.
This describes a walkthrough of a build of python 3.5.6 from a source tarball.
Just go to python.org Download section and copy the download link to a python version of your need:
tar xvf Python-3.5.6.tgz
./configure --enable-optimizations --with-ensurepip=install
make -j 8
As you see, the steps are straight forward.
The only one dependencies you have to install, are the build essential tools aka. C compiler.