Step1:  Go to the python official download page and download the python interpreter versions you are interested in.

Step2: Install them, by ctrl-clicking on the .mpkg file and choosing to open it with the installer (required to override the fact that the python interpreters are incompatible with the new Guardian secure installation system)

Step3: as described in pip installation guide:

–  issue interpreter version-specific setup tools install:

pythonX.X ez_setup.py

– install version-specific pip installation:

 pythonX.X get-pip.py

Step4: add the pip-X.X specific directory to your path:

nano ~/.bash_profile

and

export PATH=$PATH:/Library/Frameworks/Python.framework/Versions/X.X/bin

Now that you’re done, please verify that the clang is installed and is in your system path. If this is not the case you might experience some trouble installing python modules requiring to be compiled.

Add-on: to install LAPCKs and ATLAS (very useful for Scipy, follow this tutorial )