How to fix absent Python autocompletion on object instances in Vim?

I had to use the following line to get ctrl+space working

imap <Nul> <C-R>=RopeCodeAssistInsertMode()<CR>

Even though it does not use Vim’s omnicompletion plugin, by using rope, ropemode and ropevim it is possible to get autocompletion in methods:

Even though not really exactly what I wanted it works pretty well.

I got it working like so: I installed the ropevim distribution from here and added the following lines to my .vimrc file:

" Rope AutoComplete
let ropevim_vim_completion = 1
let ropevim_extended_complete = 1
let g:ropevim_autoimport_modules = ["os.*", "traceback", "django.*",  "xml.etree"]
imap <c-space> <C-R>=RopeCodeAssistInsertMode()<CR>

Now pressing Ctrl+Space will bring up the rope completion menu.