def flatmap(f, items):
        return itertools.chain(*map(f, items))

1. in Python 2 `map` is eager which — as with the previous `even` filter — may lead to unnecessary work if you only need part of the list (or a dead process if the input is infinite...). itertools.imap (or a generator comprehension) would be better. This is "fixed" in Python 3 (where the `map` builtin has become lazy and `itertools.imap` has been removed) but

2. it's being eagerly unpacked through *, itertools.chain also provides a from_iterable method which doesn't have that issue (and can be used to flatten infinite streams), introduced in 2.6

So `flatmap` would probably be better as:

    def flatmap(f, items):
        return itertools.chain.from_iterable(
            itertools.imap(
                f, items))