Short vim script that maps CTRL+j in normal and insert mode to add a new import (and sort the imports) in a Python file.

python_import.vim

function! PythonAddImportInsertLeave(insert_mode)
	execute "normal! V/import.*$\\n\\s*\\n\<CR>"
	execute "normal! !sort\<CR>"
	execute "normal! `mzz"

	" remove import auto-cmd
	autocmd! PythonAddImport *

	if a:insert_mode
		call feedkeys("a")
	endif
endfunction

function! PythonAddImport(insert_mode)
	if &filetype != "python"
		return
	endif

	execute "normal! mmgg/import\<CR>Oimport\<space>"

	augroup PythonAddImport
		execute "autocmd InsertLeave <buffer> :call PythonAddImportInsertLeave(". a:insert_mode .")"
	augroup end

	startinsert!
endfunction
nnoremap <C-j> :call PythonAddImport(0)<CR>
inoremap <C-j> <ESC>:call PythonAddImport(1)<CR>