>  Dictionaries are only pairs of data.  I assume a list can be one of 
>  those elements, but I couldn't figure out how to make it work in the 
>  structure I presented.

Yes, the object that is stored can be anything. Thus

> >> numList = [1,2,3]
> >> chrList = ['1','2','3']
> >> numDict = {}
> >> numDict['asNum'] = numList
> >> numDict['asChr'] = chrList
> >> for item in numDict['asNum']: print item,
...
1 2 3
> >>

shows two lists being stored in a dictionary.
You can also store instances of classes or functions 
or even the classes themselves!

>  I wanted to make the methods flexible enough that I wouldn't have to 
>  edit every method if the module list ever changed.  I guess I don't 
>  understand how a dictionary works in this situation.

I don;t understand what you don;t understand here. Can you 
expand on why you don't think a dictionary would work?

> > Why not write constructors that take a list as a parameter.
> > The constructor can manage its own list and the higher
> > level constructor just passes in the appropriate list. That way
> > each class only needs to know about the data at the level
> > it is responsible for. So the Module class might look a bit like:
> >
> > class Module:
> >    def __init__(self, name, componentlist):
> >         self.components = {}
> >         self.name = name
> >         for component in componentlist:
> >             self.components[component[0]] = Component(component)
> >
> > This implies that the component list is structured as a list of tuples.
>  
>  I originally had tuples, but you can't access individual elements.  

What makes you think so?

> >> t = (1,2,3)
> >> print t[0]
1
> >>

The only thing you can't do is alter the data in the tuple - which is 
exactly the behaviour you want if reading the tuple from a config file!

> >> I have object "db.mb".  I have iterator "shortmod" with a value of  
> >> "mb". Why can't I call "db.shortmod"?
> >
> > You can use db.getattr(shortmod)
>  
>  That doesn't work.  It tells me "Database instance has no attribute 
>  'getattr'".

Its actually a special method so needs the underscores __getattr__
and accessed via a function. I got my syntax muddled:

getattr(db, shortmod)

is how it should be written.

> > but I think its easier and clearer in this case to use:
> >
> > db.Modules[shortmod]
>  
>  If Modules is a class name, how am I able to call it like that?  

Modules is a dictionary of Modules in the db object. I 
should probably have used the example from my Module 
class above:

myModule.components[compname]

>  "AttributeError: Database instance has no attribute 'Modules'"

You will need to modify the definition of the database class 
to have the Modules dictionary first! :-)

Alan G
Author of the learn to program web tutor
http://www.freenetpages.co.uk/hp/alan.gauld


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