After reading all your comments and thinking a little to my specific case, I think it is definetively better to go with the "isinstance()" implementation. My objects represent mathematical function defined over a numerical grid, and I hardly think of an unrelated class objects that could be compared with them in a meaningfull way.
Thanks again to all of you for helping me to better understand another piece of the Python's world. ;-) Andrea -- http://mail.python.org/mailman/listinfo/python-list
