On Wed, 09 May 2007 23:10:19 -0500, Robert Kern wrote: > Steven D'Aprano wrote: >> On Wed, 09 May 2007 21:18:25 -0500, Robert Kern wrote: >> >>> Actually, the root cause of Peter's specific example is the fact that the >>> default implementation of __hash__() and __eq__() rely on identity >>> comparisons. >>> Two separate invocations of the same script give different objects by >>> identity >>> and thus the "history of insertions and deletions" is different. >> >> The history is the same. The objects inserted are the same (by equality). > > No, they *were* different by equality (identity being the default > implementation > equality that was not overridden in either Peter's code nor Alan's).
Ah yes, you are right in the sense that Python's notion of equality for class instances is to fall back on identity by default. But in the vernacular human sense, an instance X with the same state as an instance Y is "equal", despite being at another memory address. I was using equality in the sense that two copies of the same edition of a book are the same, despite being in different places. For the record, and for the avoidance of all confusion, I'm not suggesting that Python's default behaviour is "wrong" or even "bad", merely pointing out to all those wise in hindsight that the behaviour was extremely puzzling for the reasons I've given. But you can be sure that I'll never forget this lesson :) -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
