[Tutor] Python structure advice ?

Dave S pythontut at pusspaws.net
Thu Dec 16 19:43:52 CET 2004

Dave S wrote:

> Im sorry to bang on about Python structure, but I do struggle with it, 
> having in the past got into very bad habits with loads of BASIC where 
> everything was global, and Forth, and hand coded 8031, 8051, 6502 .... 
> I cant get my head round how you guys handle a modern structured 
> language :-)
> (PS before anyone flames me - I think Python is great and am 
> determined to learn it ;-) )
> I have ended up with my application in several separate directories.
> I have 'live_datad' a demon that extracts web data, at preset times 
> and archives it, this will be run as a thread, and possible using a 
> queue ... (still digesting info from query about IPCing)
> I have a 'data_core' which accepts data from either live_datad real 
> time or the archive for testing, it builds up a large multi 
> dimensional array with various pointers into the array.
> I have a statistical module 'data_stats' which analises the array 
> pulling various stats.
> And finally I have an analytical module 'data_predict' which using the 
> output from 'data_stats' & data directly from the 'data_core' outputs 
> statistical predictions of future data.
> I have written my 'live_datad', I have written my 'data_core' & have a 
> fairly good idea how to write the rest.
> My problem is that pretty much all the modules need to fix where they 
> are when they exit and pick up from that point later on, ie more data 
> comes from live_datad, it is passed to 'data_core' which updates the 
> matrix, then 'data_stats' then 'data_predict'  all called form the 
> main script.  This OK till the main script realizes that more data is 
> avalible from 'live_datad', passes it to 'data_core' which must 
> remember where it was and move on, and the same for the rest of the 
> modules. To make the problem more acute the modules may not be called 
> in exactly the same order depending on what I am trying to achieve.
> The 'remembering where is was' seems a continuous stumbling block for 
> me. I have though of coding each module as a class but this seems like 
> a cheat. I could declare copious globals, this seems messy, I could 
> define each module as a thread & get them talking via queues, given 
> this serious thought but heeded warning in previous posts. I have 
> thought about returning an list of saved 'pointers' which would be 
> re-submitted when the function is called. I don't know which way to turn.
> With my code now running to a few hundred lines (Don't laugh this is 
> BIG for me :-D ) I am going to have to make a structure decision and 
> any suggestions would be appreciated.
> How would you approach it ?
> Dave
> _______________________________________________
> Tutor maillist  -  Tutor at python.org
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Having written this email, it has put my thoughts in order, though it 
seems a bit cheaty, wouldn't defining all modules that have to remember 
their internal state as classes be the best bet ?


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