Thank you all very much for your responses. It's especially reassuring to hear about other Python GA's as I have had some scepticism about Python's speed (or lack of it) being too big a problem for such an application.
With regard to using numeric, arrays or integer lists -- I didn't mention that these strings can also contain wild cards (so I suppose it's not really binary -- sorry). This is traditionally done using a '#' symbol, but I was imagining using a value of None in a boolean list to represent this. Also there is currently a fair bit of research going into other representations (floating-point values, paired values etc) so I was hoping to be able to keep my framework extensible for the future. Many thanks again for your help. I will ``take the plunge'' and give the boolean list a go I think! -- http://mail.python.org/mailman/listinfo/python-list