On Thu, 14 Aug 2008 20:44:32 -0700, castironpi wrote: > For > > a= 6 > b= a > > the test > > a is b > > should clearly return true.
Since Python promises not to make a copy of a when you execute "b = a", then I think that such behaviour is guaranteed by the language. > Python distinguishes what mathematics does > not, between identity and equality. Clearly 5+4 and 6+3 - evaluate- to > the same, but math doesn't define whether they are the same, and in some > sense the question isn't asked ordinarily, or isn't debated. I want to > infer that math doesn't define the 'is' relation as Python knows it. Mathematicians often *define* equality as identity. That certainly makes sense when dealing with numbers -- what would it mean to say that there are (say) three different instances of the abstract integer 42, all equal yet not identical? I suggest that this simply doesn't make sense -- it is "not even wrong". Equality-as-identity may not hold in all areas of mathematics, but I think it is safe to say it holds for ideal (abstract) numbers, as opposed to implementations of numbers as bit patterns or objects in memory. http://en.wikipedia.org/wiki/Equality_(mathematics) -- Steven -- http://mail.python.org/mailman/listinfo/python-list
