Newbie question: how to determine "is-a" relationship

[Jake Baker]

Gosh. I've been using Python since 96 and I don't know this! Wow!

Say I have a class heirarchy that looks like A, B <- A, C <- A, etc....

I have a list of objects (which I know arbitrarily are all A or sublasses of A) and want to filter them based on which subclass they are.

How do I go about doing this? You help is greatly appreciated!

Thanks,
 - Jake Baker