Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail
From: Vincent Davis <vincent@vincentdavis.net>
Newsgroups: comp.lang.python
Subject: Re: shorten "compress" long integer to short ascii.
Date: Fri, 20 Nov 2015 07:18:55 -0700
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On Thu, Nov 19, 2015 at 9:27 PM, Paul Rubin <no.email@nospam.invalid> wrote=
:

> You can't improve much.  A decimal digit carries log(10,2)=3D3.32 bits
> of information.  A reasonable character set for Twitter-style links
> might have 80 or so characters (upper/lower alphabetic, digits, and
> a dozen or so punctuation characters), or log(80,2)=3D
>

=E2=80=8BWhere do I find out more about the how to calculate information pe=
r digit?
=E2=80=8B
Lots of nice little tricks you used below. Thanks for sharing.


> Here is my shortened version:
>
>   import string
>
>   # alphabet here is 83 chars
>   alphabet =3D string.ascii_lowercase + \
>        string.ascii_uppercase +'!"#$%&\'()*+,-./:;<=3D>?@[]^_`{|}~'
>   alphabet_size =3D len(alphabet)
>
>   decoderdict =3D dict((b,a) for a,b in enumerate(alphabet))
>
>   def encoder(integer):
>       a,b =3D divmod(integer, alphabet_size)
>       if a =3D=3D 0: return alphabet[b]
>       return encoder(a) + alphabet[b]
>
>   def decoder(code):
>     return reduce(lambda n,d: n*alphabet_size + decoderdict[d], code, 0)
>
>   def test():
>       n =3D 92928729379271
>       short =3D encoder(n)
>       backagain =3D decoder(short)
>       nlen =3D len(str(n))
>       print (nlen, len(short), float(len(short))/nlen)
>       assert n=3D=3Dbackagain, (n,short,b)
>
>   test()
>




Vincent Davis
720-301-3003