Some times we need specific python version for specific project.There are some easy way to install specific python version through virtualenv. In below I try to give two example to install python2.7 and python3.5

Example one:
If you are already install virtualenv then write the code for make a virtualenv that will have python version 2.7

mkvirtualenv --python=python2.7 virtualenvname

Example two:
Now we will create a virtualenv that will base on python3.5

mkvirtualenv --python=python3.5 virtualenvname