pure virtual functions in python

[Delaney, Timothy]

> From: polux [mailto:polux2001 at wanadoo.fr]
> 
> how to emulate them ?
> I mean, how to force a user to redifine some functions in a derivated 
> class ?

Most responses have used `NotImplementedError`. This is fine, and useful if
you want the abstract class to document what methods it defines.

The other approach is to document what attributes/methods other functions
require their parameters to have. This achieves the same effect (but throws
an `AttributeError` rather than a `NotImplementedError`), but is in many
ways more versatile.

I have never used `NotImplementedError` in my python code. Why bother?

Tim Delaney