Convert to binary and convert back to strings

[Paul Rubin]

Steven D'Aprano <steve at REMOVEME.cybersource.com.au> writes:
> For a short string like "Python", using an array is a tiny bit slower, at
> the cost of more complex code.... if you're converting a long string,
> using array is faster. If it is a short string, it doesn't make much
> difference.

I modified your array version slightly:

    def flip3(text):
        n = len(text)
        mask = ord('U')
        text = array('b', text)
        for i in xrange(n):
            text[i] ^= mask
        return text.tostring()

and I got flip3("Python") a little faster than the listcomp version,
but yeah, I was concerned mostly about long strings.

For fixed-sized short strings, using array('l') and unrolling the loop
makes a big difference:

    text = "Pythonic"
    mask = array('l','UUUU')[0]

    def flip4(text):
        text = array('l', text)
        text[0] ^= mask
        text[1] ^= mask
        return text.tostring()

>>> timeit.Timer('flip1(text)', setup).repeat()   # your version
[35.932021141052246, 36.262560844421387, 40.019834041595459]
>>> timeit.Timer('flip3(text)', setup).repeat()   # flip3 above
[33.44039511680603, 31.375681161880493, 31.374078035354614]
>>> timeit.Timer('flip4(text)', setup).repeat()   # flip4 above
[15.349261045455933, 15.526498794555664, 15.351589202880859]

See http://www.nightsong.com/phr/crypto/p3.py for an encryption
routine written this way.