hi Tal and Terry,
  
I hadn't noticed that continuing to type does go to the appropriate spot.  However, I see what I think are two or three bugs (not sure is 'a)' is a bug) in the behavior:

  a) on my system it does not visibly filter the list. EG, if I type 'os.', wait for the popup, then type ge (so, 'os.ge') it scrolls down to, and selects, "get_blocking", but the rest of the list is still there.  
  This is still useful but, Tal, I'm just pointing out that I don't see any options disappear (as I think you're saying they should).  Should the list really be visibly filtered?

  b) say I want os.get_terminal_size.  I type "os." and wait for the popup to appear (see 'c)' for why this is necessary); then I type 'get_t".   Now  "get_terminal_size" is visible and selected but autocompletion doesn't occur.  I.E., I still have 'os.get_t" below the popup.  To get the full word I have to arrow *away* from the correct answer and then arrow back to it.  Now "get_terminal_size" appears below the popup.  This is obviously less serious, and less mysterious, than the original hang issue, but it's still a usability issue.

  c) Terry: regarding "Box comes up after cntl-space or time delay after key char." On my IDLE, the box *never* appears if I initially type beyond the ".".  E.G.
   import os
   type "os.g" and wait.
      RESULT: the popup never appears.  It will appear if I then do "cntl-space" but not from a time delay.  This seems like another biggish usability bug.  The time delay should work (as I think you're saying) and obviously "cntl-space" isn't something a newbie is likely to know to try.