En Mon, 14 May 2007 12:35:16 -0300, elventear <[EMAIL PROTECTED]> escribió:
> Since I am defining a hash for my object, it makes sense that I should > be able to define equality. But I am not sure about inequality, in my > specific case. The paragraph above mentions that __cmp__ should be > defined if I define a __hash__, but in the default behaviour of > __cmp__ inequality is included. So what should I do? Also why is > equality necessary to be defined? Do dicts only use __hash__ or do > they use equality as well? Dicts and sets use the key's hash value to determine the "bucket" where the key will be placed, and == to distingish between different objects with the same hash value. That is, you should define __hash__ and one of (__cmp__ or __eq__). __neq__ (inequality) isn't required nor used by dict/set implementation. (Anyway, Python will transform a!=b into not(a==b), if __neq__ isn't defined). Neither <, <=, >, >= are used. The important thing is that, if two objects compare equal, they must have the same hash value. That is: (a==b) => (hash(a)==hash(b)) (the reciprocal is not true). -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
