On PyDev the auto-assist is turned on by default (with the current structure).
It mostly does what Daniel said, adding all characters to the auto activation, but after trying to use that on JDT, I didn't find it really fluid to use. My issues were:
1. Highly tune completions for speed (if it's slow to compute, it becomes annoying to use -- async can help, but it has to be tested, it may end up being annoying to use anyways).
2. Don't apply the completion on '.' (rather, put a dot at that point and request a new completion -- maybe there's a way to do this, but I didn't really search much due to point 1.)
As a note, on PyDev, all completions are required to implement ICompletionProposalExtension (so, after a first invocation it's mostly filtering -- I had to do some workarounds related to sorting to resort whenever a new char is entered in this case, as the PyDev sorting takes into account many things such as if it starts with the exact qualifier, which changes as the user keeps typing as the completion engine can match some completions by substrings), but this means that even if PyDev slows down a bit sometimes to compute the initial set of completions -- which should be rare -- it'll stay fast afterwards (I think this is probably required for any plugin that wants to provide auto-assist on any char).
The only downside is that users need to know that <Shift+Enter> should be used to enter a new line as <Enter> will apply the current completion -- that's the first tip I always give to users:
http://www.pydev.org/manual_101_tips.html ;)
Best Regards,
Fabio