From: michael libby <x@...>
Date: 2002-09-19T22:02:24+09:00
Subject: Re: Is better to subclass or to add methods to an existing class?

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On Thursday 19 September 2002 07:20, Vincent Foley wrote:
[example modification of existing class snipped]

> But my friend told me that Python didn't have that because it was not a
> good thing and it was not the proper way to do it.  He said that the
> true way of doing it, is to subclass (since Python 2.2 can now subclass
> builtin types) the base class:

[python code removed... washing hands...]

> His main argument was just that, "It's the Wrong Way (TM) to do it".  To
> me, it just seems like extra code and added complexity.

It is the Right Way To Do It if your code passes all its unit and 
acceptance tests. It is the Wrong Way To Do It if your code fails to 
perform as expected. Beyond that, who cares?

You might perform some trivial benchmark to compare the two on a variety of 
base classes and a variety of common "extensions" and reach some overall 
efficiency conclusion, though.

> Can you enligthen me and tell me if it's really that bad an idea to add
> methods to an existing class, or if he's just being a Python zealot?

Nope, can't say. ;)

Personally if I have a function that takes a string and only a string (like 
the example Rot13) then I would extend the String class. Otherwise, while 
programming, I have to remember if my strings (lowercase) are Strings or 
MyStrings in order to remember which methods they have access to.

But it depends on the application. Maybe in some cases I want two separate 
kinds of strings.... kind of like how we have lots of separate kinds of 
numbers. 

 -michael

++++++++++++++++++++++++++++++++++++++++++
Michael C. Libby <x@ichimunki.com>
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