Supposedly Python 2.7 is included native to OSX 10.8 and above (if I remember correctly), but I recently installed Python 3.5 to use for projects while I work through UDacit
You can also use Anaconda for maintaining two versions of Python:
Download Anaconda for both Python versions
Open .bashrc
Add the path to new Anaconda you have installed for, e.g.:
export PATH="/home/paras/anaconda3/bin:$PATH"
Now there will be 2 export paths: one for Python 2 and one for Python 3. Comment the one which you don't want.