http://stackoverflow.com/questions/104420/how-to-generate-all-permutations-of-a-list-in-python

permutations.vim

function! Permutations(list)
  let len = len(a:list)
  if len == 0
    return [[]]
  elseif len == 1
    return [a:list]
  endif
  let list = []
  for perm in Permutations(a:list[1:])
    let list = s:push(list, [a:list[0]] + perm)
    for i in range(len - 1)
      let list = s:push(list, perm[:i] + [a:list[0]] + perm[(i + 1):])
    endfor
  endfor
  return list
endfunction