Make use of vim's "conceal" feature to replace certain language keywords with unicode characters. Just for pure eyecandy. This does not replace your source code at any point.
Use of a plugin manager like Pathogen, Vundle or NeoBundle is recommeded for installation. Or you can just simply copy the repesctive syntax file (e.g. python.vim) in ~/.vim/after/syntax folder.
Plugin is inspired by http://github.com/Twinside/vim-haskellConceal