Yeah, that looks like a pretty decent summary to me. I wonder if this would be worth posting on the Wiki somewhere? Maybe:
http://www.python.org/moin/DictionaryKeys
That makes it easy to point to when this issue comes up again.
The page may also want to mention an extant bug with new-style classes.
The behaviour is *meant* to be:
1. Class defines none of __cmp__, __eq__ or __hash__:
Default behaviour allows the class to be used as an identity-based dictionary key.
2. Class defines __hash__ and __cmp__ (or __eq__):
Class is usable as a dictionary key, with semantics governed by developer supplied methods.
3. Class defines __cmp__ or __eq__, but NOT __hash__:
Class cannot be used as a dictionary key, as the default hash may not be valid for the developer supplied comparison operation.
For classic classes, this works as expected. For new-style classes, case 3 doesn't work properly - the default hash is inherited from object anyway.
This *is* a bug (since Guido called it such), but one not yet fixed as the obvious solution (removing object.__hash__) causes problems for Jython, and a non-obvious solution has not been identified.
Cheers, Nick.
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Nick Coghlan | [EMAIL PROTECTED] | Brisbane, Australia
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http://boredomandlaziness.skystorm.net
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