How to install specific python version on virtualenv

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