sort(cmp=func)

[norseman]

Tobiah wrote:
> I have a list of objects that generate code.  Some
> of them depend on others being listed first, to 
> satisfy dependencies of others.
> 
> I wrote a cmp function something like this:
> 
> def dep_cmp(ob1, ob2):
> 	
> 	if ob1.name in ob2.deps:
> 		return -1
> 	else:
> 		return 1
> 
> I also tried returning 0 when there were no dependency
> relationships between the objects.
> 
> This failed, because every object was not compared with
> ever other.  I imagine that this is because sort assumes
> that if a > b and b > c, then a > c.  In my case, this
> isn't really true.  If a is not dependent on b, and
> b is not dependent on c, that doesn't mean that a is not
> dependent on c.
> 
> Is there a better way?
> 
> Thanks
> 
> Tobiah
> ** Posted from http://www.teranews.com **
> --
> http://mail.python.org/mailman/listinfo/python-list
> 

==================================

If you are running Linux take a look at 
/lib/modules/[kernel-ver]/modules.dep

In other words, to create a list like:
this module:              depends on these
module-a                  module-f, module-g

copy ALL modules to a scratch directory
ls -1 | sort >file.lst
(or dir /b/l | sort >file.lst)
concept:
#outer loop
get a filename from file.lst
create a list of all imports in it
compare filename, in turn, to each line in file
if it finds itself loop
#inner loop
otherwise open module and create 2nd list of all imports in this file
compare each item in list one to each item in list two and output
   one line for each match to imports1.lst, format:
      module name needing, module name wanted  (filenames not def names)

#outer loop2
get a line from dep1.lst
parse to f1=first-name, f2=second-name
create list of imports for f2
#inner loop2
check each import of f2 against name of f1
if there is a match, print  Circular conflict with: f1 and f2 to
   problems.lst

A sort on second filename on line combined with a visual inspection will 
often help point out any 3-way (or more) circulars.
(a needs b needs c needs a)  No guarantees, though.

You will have to resolve circulars yourself. Usually involves changing 
code.  If A needs output from B to run and B needs output from A to run 
you have an obvious circular. Rewrite/fix the code.

Perhaps make a lib file of all the imports for the project.  (Which is 
the preferred practice.)  Load it with the main logic. Thus none will be 
run until all are present. Then eliminate whatever circular nonsense 
still exists...

If problems.lst is empty all that needs to be done is for each import to 
check the dep1.lst and first load the second filename on the line for 
each first-name matching module wanted.  For a given first filename not 
being in a circular, manual ordering of the dep1.lst can be done if 
needed.  (Perhaps f1,a1:f1,b1:f1,c1  needs to be f1,c1:f1,a1:f1,b1 ? 
Simply because descriptive alpha name sort winds up being wrong load 
sequence.)

Just because a piece of code can be reused does not mean it is 
generically practical to do so.  The why of this is your current problem.

My first reaction to your original post is that you inherited something 
and are setting about cleaning it up so you can work on it.


Best of luck. Succeed and you get to claim another T-shirt. :)


Steve
norseman at hughes.net