[BangPypers] Pythonizing an algorithm

Senthil Kumaran orsenthil at gmail.com
Thu Dec 4 10:51:50 CET 2008

On Thu, Dec 4, 2008 at 3:07 PM, Shashi <connect2shashi at gmail.com> wrote:
>        http://manpages.ubuntu.com/manpages/hardy/man5/deb-version.htm
> in the Sorting Algorithm section... I can't
> understand a little bit of it... Please help

Did not look at the code and went to algorithm to see what it is.
It seem fairly straight forward. I shall try to explain step by step
and try it out in code.


The strings are compared from left to right.

        First the initial part of each string consisting entirely of  non-digit
        characters  is determined.  These two parts (one of which may be empty)
        are compared lexically.  If a difference is found it is returned.   The
        lexical comparison is a comparison of ASCII values modified so that all
        the letters sort earlier than all the non-letters and so that  a  tilde
        sorts  before  anything, even the end of a part.  For example, the fol‐
        lowing parts are in sorted order: '~~', '~~a',  '~',  the  empty  part,

        Then  the  initial  part of the remainder of each string which consists
        entirely of digit characters is determined.  The  numerical  values  of
        these  two  parts are compared, and any difference found is returned as
        the result of the comparison.   For  these  purposes  an  empty  string
        (which  can  only occur at the end of one or both version strings being
        compared) counts as zero.

        These two steps (comparing and removing initial non-digit  strings  and
        initial digit strings) are repeated until a difference is found or both
        strings are exhausted.


1) use regex to split the strings to non-digits ( not alpha) and digits.
2) get the length of the non-digits obtained and the digits string obtained.
3) as the example says, Before doing a string compare, run through to
compare ~ and empty string. Whichever has more ~ or empty string is
4) next Do string compare.
5) come to digits portion. Set empty string as Zero and do a numeric
compare and figure out which one is greater.



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