filtered and non-filtered elements in a single pass

Try this, using iterators:

from itertools import tee

def partition(lst, pred):
    l1, l2 = tee((pred(e), e) for e in lst)
    return (x for cond, x in l1 if cond), (x for cond, x in l2 if not cond)

Use it like this, and remember that the values returned are iterators:

lst = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
evens, odds = partition(lst, lambda x: x%2 == 0)

If you need lists for some reason, then do this:

list(evens)
> [0, 2, 4, 6, 8]
list(odds)
> [1, 3, 5, 7, 9]

def someFunc(trueorfalsefunc, l):
    trueList = []
    falseList = []
    for item in l:
        if trueorfalsefunc(item):
            trueList.append(item)
        else:
            falseList.append(item)
    return trueList, falseList

So, for example:

>>> someFunc(bool, [1,2,0,"", "a"])
([1, 2, 'a'], [0, ''])

If you want to go for a one liner you can do this: (I'm switching from dicts to lists as Niklas B. suggested to improve readability)

>>> some_list=[True, False, True, False, False]
>>> reduce(lambda (true,false),x: (true + [x], false) if x else (true, false + [x]), some_list, ([],[]))
([True, True], [False, False, False])

You could use generator comprehensions, which should help on performance and facilitate cleaner code. I really am not sure if this will be satisfactory for the rest of your program though. It depends on how you're using these returned results.

trueList = (elem for elem in list if trueOrFalseFunc(elem) )
falseList = (elem for elem in list if elem not in trueList )