Fix my screwed up Python indentation in vim

fixmyindent.vim

" initially i was using 3-space (shiftwidth=3) indentation with noexpandtab, and tabstop=8, the default
" this switches it to proper 4-space indentation with expandtab

" convert tabs to spaces
set tabstop=8
set shiftwidth=3
set expandtab
retab

" convert spaces to tabs
set tabstop=3
set noexpandtab
%retab!

" final convert tabs back to spaces
set tabstop=4
set shiftwidth=4
set expandtab
retab