The following code cannot select when press OK return null
from appuifw import *
tuple = appuifw.multi_selection_list([u'aa',u'ab',u'ac'], style='checkmark')
Please note than when you use style='checkmark' the selection is done by pushing two keys together:
+ the "abc key" (sorry I'm not sure this is the proper name, it could be even with a pencile icon)
+ the mouse