
Re: list mutability (very basic question)
Posted:
Sep 23, 2013 2:44 AM


I missed the beginning of this thread, but I just wanted to note that the confusion is deepened when you contrast evaluating
{0}[[1]]
which causes an error, with evaluating each of the following two sequences of inputs:
x = {0}; x[[1]] = "Hello"' x {Hello}
{0}[[1]] 0
On Sep 22, 2013, at 2:47 AM, Alan G Isaac <alan.isaac@gmail.com> wrote:
> On 9/21/2013 10:15 AM, Bob Hanlon wrote: >> Attributes[Set] >> {HoldFirst, Protected, SequenceHold} > > > Thanks, but I'm still unclear: > why does ``{0}[[1]]=1`` raise an error? > > As a point of reference for my confusion, > Python behaves in a way I find more intuitive: > ``[0,1][1]=0`` does not raise an error. > (This becomes an interesting difference when > we get to argument passing in Mathematica, where HoldFirst > becomes useful as a way to allow "in place" modification.) > > Back to Mathematica, am I understanding correctly that after > ``Set[Part[x,1],1])`` that x still references the > same location in memory? How can I easily see that? > (E.g., in Python, I would us the ``id`` function.) > > Thanks, > Alan Isaac
 Murray Eisenberg = murray@math.umass.edu Mathematics & Statistics Dept. Lederle Graduate Research Tower University of Massachusetts 710 North Pleasant Street Amherst, MA 010039305

