I have a custom "go to definition" shortcut that works great in python (using ropevim) but when I'm in a coffee-script file I need to use the normal ctags lookup to navigate around. Would it be possible to make just one shortcut that did either a ropevim lookup OR a ctags lookup depending on the file type that is open in the current buffer?
You can put if/endif tests in your mappings by way of :execute but that's a bit messy.
What you should do instead is define your mappings in filetype-specific autocmds (see :h autocmd):
autocmd FileType python nnoremap this that
or, better, define them in ~/.vim/after/ftplugin/python.vim (and another file for coffeescript and so on):
nnoremap <buffer> this that