breaking up is hard to do

Charles Hartman charles.hartman at conncoll.edu
Fri Mar 25 23:44:59 CET 2005


On Mar 25, 2005, at 5:16 PM, python-list-request at python.org wrote:

>
> For example I have a class named Indicators. If I cut it out and put it
> in a file call Ind.py then "from Ind import Indicators" the class can
> no longer see my globals. This is true even when the import occurs
> after the config file has been read and parsed.

I'm new enough at this myself so that (a) I understand how you get into 
this problematic situation and (b) you should take what I say with a 
spoon or two of salt.

I find it most useful to think of the problem as *getting rid of global 
variables*. (Compared with some other languages Python practically has 
no globals; module is the most global scope there is.) That means (1) 
designing some kind of clear and efficient package for data that you 
can pass back and forth between classes and modules; and (2) 
redesigning the classes themselves. The redesign is aimed at narrowing 
down how everything gets and sends data -- no more grabbing into the 
global air, but referring to some specific data package (which may be 
an instance of a special class).

The nice thing about this is that by implementing it, you're 
automatically greatly increasing the "object oriented" qualities of the 
program, with the consequent gains: modularity, clarity of interface . 
. . It tends to make the whole program's design clearer and clearer. So 
the rigors you go through in the redesign really pay off in your own 
understanding of your own program -- especially six months later.

I'm sure people who know a lot better what they're talking about will 
have more thorough answers for you.

Charles Hartman




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