Designing questions

[Gordon McMillan]

Pierrette writes:

> I'm writing  a application wich contains abouth 50 inputscreen
> linked to db-tables. Each inputscreen has 2 classes - 1 GUI class
> wich  construct the screen. - 1 db class wich  do the db acces.

I remember you!
 
> All the gui-classes are done at the moment, so i have the prototype
> of the application. And here's my problem : The source code becomes
> realy long, wich gives a long time to load it. I was thinking of
> spliting it in modules (1 module for each screen wich contains the
> gui-class and the db-class) and then importing it when i needed it,
> this is when the user makes the choice in the main-menu. The
> question i have is how to 'unload' a module when i don't need it
> anymore ? If i don't unload a module i would  have as many modules
> in memory as the user has made choises in the main menu. I think
> this could become a memory problem especailly since i'm using gadfly
> as db, wich allso holds the tables in memory.

Well, you don't unload modules in general, and I bet it won't be a 
problem. You will gain a lot of speed, because for imported modules, 
Python will create a .pyc the first time it's imported, and use that 
(if the .py file hasn't changed) on subsequent imports.

In other words, one way to speed up loading is to create a very small 
main script:
-----------------------------
import myrealstuff
myrealstuff.run()
-----------------------------

This script will be interpreted each time, but "myrealstuff" will get 
pre-compiled.
 
Breaking up your script is a good idea for maintainability, too. But 
rather than just chop it in pieces, I'd look carefully to see if all 
those GUI classes don't have some things in common that can be 
factored into a base class. Then each GUI class can inherit from 
that, and just add the stuff that's particular to that screen. 

You could use the same idea on the db classes, too, but I'd guess 
that most of your code is GUI code. With gadfly, make sure you use 
the form of SQL that uses "?"s to mark the variables. That will let 
gadfly precompile the SQL statements.

> I really would appreciate some hints and comments here from
> experienced guys who allready wrote BIG real world applications in
> PYTHON.

That's me. Big guy, big Python <2.0 wink>

- Gordon