Peter Hansen <[EMAIL PROTECTED]> wrote: > > But the problem is still there: how do you know what > > it looks like before you treat it as a cat? isinstance(), , as Steve > > state, is too rigid. > > The argument is that you probably don't really need to know > what it looks like *before* you try to use it, even if you > think you do. The cases where you really do are probably those > Alex Martelli's recipe (mentioned near the start of the thread) > is intended to help. (Specifically, avoiding the situation > where the object implements the required protocol only partially, > but you don't find that out until you've already started using > the object, possibly corrupting it in the process.)
Exactly. The recipe's still in the CB 2nd edition (which I should be editing right now instead of doing usenet, with deadline so terribly close and lots of enhancements left to do, but hey, it IS 1:30 AM, I deserve a little break;-). The right solution is adaptation (PEP 246, Eby's PyProtocols, etc), but until we can convince Guido of that, so that adaptation becomes widespread, duck typing, and occasionally (when needed) "accurate LBYL" remain the best approach. And don't forget unit-tests -- see Robert Martin's now-famous article at http://www.artima.com/weblogs/viewpost.jsp?thread=4639 . Alex -- http://mail.python.org/mailman/listinfo/python-list
