User hook called when menu-complete displays a completion?

[dandavison]

Is there any way to execute user code each time menu-complete displays the next completion?

E.g. in the script below, if I hit tab repeatedly, it cycles through displaying "a" and "b". I would like some of my python code to execute when it displays "a", and when it displays "b".

import rl

def complete(text):
    return ['a', 'b']

rl.completer.parse_and_bind('tab: menu-complete')
rl.completer.completer = rl.generator(complete)
raw_input()

In the readline C code I see, e.g. a call to display_matches (which itself calls rl_completion_display_matches_hook) in rl_menu_complete, but I am not entirely sure whether what I want is possible and wanted to check.

Thanks!