New Features in Python 1.6

Fredrik Lundh effbot at telia.com
Tue Apr 4 22:05:47 CEST 2000


Philip Newton wrote:
> >why not just use two different compression algorithms repeatedly,
> >until you've squeezed the file down to a suitable size?  it takes a
> >little work, but you can design them so that one of them can always
>                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> >strip away at least one bit from the input stream.
>  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> Yes? I challenge you to provide any algorithm that will strip away one
> bit from the four sequences 11, 10, 01, and 00, while still being able
> to restore the previous state.

okay, okay, I shouldn't have posted that several days after
april 1st...  but hey, this group is (indirectly) named after a
infamous comedy troupe, so what did you expect?

anyway, here's the code:

    n = number_of_bits
    while n > minsize:
        if skip_false_bit():
            print "used algorithm 1"
        elif skip_true_bit():
            print "used algorithm 2"
        else:
            raise IOError, "deranged data"
        n = n - 1

where skip_false_bit() and skip_true_bit() returns true if
the succeed to actually compress the data.

to decode, just call insert_false_bit() and insert_true_bit()
repeatedly, in the *right* order ;-)

</F>





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