[Tutor] Subclassing vs. stand alone functions

[Kent Johnson]

chrispython at mac.com wrote:
> Hi there,
> 
> I am new to Python and trying to get my head around the OO stuff. I
> guess my question is - when do you go with subclassing vs. making a
> standalone function?

> Let's say you want to load a dictionary. Do I create a function that
> accepts some argument (say a file name) and returns a dictionary, or
> do I subclass dict and override the __init__  and __setitem__
> functions to make 'self-loading' dictionary? It seems the end result
> is the same.

I tend to reserve OOP for the cases where it provides a clear benefit 
and use a procedural style otherwise. So in this case I would make a 
separate factory function to load the dictionary because it is simpler. 
Also you are not changing the behaviour of your new dict so overriding 
seems unnecessary. (BTW Why would you override __setitem__?)

There are many cases where OOP has a clear benefit in simper code, 
encapsulation or reusability. There are times when you have to use OOP, 
for example when using a library that is specialized by subclassing, 
such as a GUI library or the cmd package.

There are also many cases where OOP just adds unneeded complication to 
your code; in these cases Python lets you write in the simpler 
procedural style.

I have written more on this topic here:
http://personalpages.tds.net/~kent37/stories/00014.html

Kent