2008/11/12 Joe Strout <[EMAIL PROTECTED]>: >> If you need to know that it walks like a duck, mates like a duck and >> tastes like a duck when roasted, you probably want it to really /be/ a >> duck and should go back to inheritance. > > I can't agree; there are times when inheritance just won't do, for example > when you don't have control over the object creation, because they come from > some factory method you can't change. In that case you may need to make a > wrapper instead of a subclass, but if you've faithfully implemented the > interface of the original class, you should be able to use it wherever the > original class could be used (within reason).
And then the original class definition changes -- new members added -- but the ones from the factory class don't change, and so are no longer compliant with the the factory class (which doesn't support the new "form_pun_relating_to_avoiding_a_high_hazard()" method) . Fine. If you checked for all the members of the class that your code uses, it makes no difference. ABCs give you a way of doing this, but in their absence it's a long list of checks. If you /can/ use inheritance then it saves having to do those checks. -- Tim Rowe -- http://mail.python.org/mailman/listinfo/python-list
