It seems to me that both Mike's and Fuzzyman's objections were that sometimes you want the current behaviour, of saying that two objects are equal if they are: 1. the same object or 2. have the same value (when it's meaningful). In both cases this can be accomplished pretty easily: You can do it with a try..except block, and you can write the try...except block inside the __contains__ method. (It's really pretty simple: try: return a == b except TypeError: return a is b ) Also, Mike said that you'll need an idlist object too - and I think he's right and that there's nothing wrong with it. Note that while you can easily define the current == behaviour using the proposed behaviour, you can't define the proposed behaviour using the current behaviour. Also note that using the current behaviour, you can't easily treat objects that do define a meaningful value comparison, by identity. Also note that in the cases that you do want identity-based behaviour, defining it explicitly can result in a more efficient program: explicit identity-based dict doesn't have to call any __hash__ and __eq__ protocols - it can compare the pointers themselves. The same if you want to locate a specific object in a list - use the proposed idlist and save yourself O(n) value-based comparisons, which might be heavy. Noam
-- http://mail.python.org/mailman/listinfo/python-list
