On Tue, Apr 8, 2014 at 1:26 AM, Paul Kölle <pkoe...@gmail.com> wrote: > It seems a tuple's immutability is debatable, or is this another instance of > the small-integer-reuse-implementation-detail-artifact? > > Python 2.6.6 (r266:84292, Dec 26 2010, 22:31:48) > [GCC 4.4.5] on linux2 > > Type "help", "copyright", "credits" or "license" for more information. >>>> a = ([1,2],[3,4]) >>>> b = a >>>> a is b > True >>>> a == b > True >>>> c = (1,2,3) >>>> d = (1,2,3) >>>> c is d > False >>>> c == d > True
That's nothing to do with mutability or reuse. With a and b, you assigned one to be the same as the other, so they are by definition identical (and equal; tuples assume that identity implies equality, even though that may not be true of their elements). With c and d, you assigned separate tuples, so they're allowed to be separate objects. I'm not sure if they're allowed to be constant-folded, but CPython apparently isn't doing so. They are still equal, though; they contain equal elements, ergo they are equal. (Note that (1, 2, 3) and (1.0, 2.0, 3.0) are equal, but they obviously can't be identical any more than "1 is 1.0" can ever be True.) ChrisA -- https://mail.python.org/mailman/listinfo/python-list
