PyCon 2011: How Dropbox Did It and How Python Helped

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.