Hi Nils, On 2013-02-17, Nils Bruin <nbr...@sfu.ca> wrote: > Wouldn't it be possible to accomplish this by assigning hash_by_id to > tp_hash in, for instance, unique_representation_c.__cinit__?
> Given the > order in which python executes __alloc__ on extension types, I think > that would still offer subclasses to set tp_hash to another value if > they want. Question: Do we *want* that subclasses can override it? After all, if they are sub-class of UniqueRepresentation, then they are supposed to show the unique representation behaviour---which includes that comparison is by identity. That's why I suggest to separate the two features of UniqueRepresentation: Cache on the one hand, comparison by identity on the other hand. If one wants another hash or another comparison, then one should inherit from the to-be-created CachedRepresentation, and not from UniqueRepresentation. > In fact, if you simply *don't* define hash on unique_representation_c, > wouldn't you get this hash anyway? (equality on "object" is by > identity). I think yes. But what happens if you want "a < b" work in a specific way? You would probably override __cmp__ (at least this is what many classes do), and if one overrides __cmp__ without providing __hash__, then you can't use it in a dictionary. Cheers, Simon -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at http://groups.google.com/group/sage-devel?hl=en. For more options, visit https://groups.google.com/groups/opt_out.
