From my understanding, the any() version is faster is primarily because it avoids looking up .update() method each iteration. The usual Python way of optimizing such cases is:

    # the original slow version
    # 2.87753200531 sec
    def run():
        _md5 = hashlib.md5()
        for i in itertools.repeat("foo", 10000000):
            _md5.update(i)


    # slight change
    # 1.82029104233 sec
    def run():
        _md5 = hashlib.md5()
        update = _md5.update

        for i in itertools.repeat("foo", 10000000):
            update(i)


    # using any()
    # 1.50683498383 sec
    def run():
        _md5 = hashlib.md5()
        any(itertools.imap(_md5.update, itertools.repeat("foo", 10000000)))

- imap returns an iterator, any is used to "force" the iterator run through all elements.

- the loop runs on C because of any. Instead of a for loop where jump and body are repeatedly evaluated by the interpreter, any consumes the iterator through a loop implemented in C.