list vs tuple

[Chris Tavares]

"deadmeat" <root@[127.0.0.1]> wrote in message
news:uGqx6.1052$p5.3997 at news1.rivrw1.nsw.optushome.com.au...
> > - There is an difference between "copy" and "deep copy". What happens if
> > you make copy a structure that contains pointers in it?
>
> then you got a problem :)
>
> but thats not the point - which when the statement a = b copies the data
> across for one type it's expected to do it for others.  It doesn't, so
it's
> inconsistant, contrary to the original claim.
>

Here's the root of your problem. a = b does NOT, I repeat, does NOT do any
data copying!!!!!

When you do this:

a = 5

You've now got a name, a, that points to an integer object out on the heap.
Similarly, when you do:

b = 9

b now points to an integer object out on the heap. And then, when you do:

a = b

a and b now point to the same integer object 9, and the integer 5 gets
garbage collected at some unknown point in the future.

So, when you do this with lists:

a = [ 1, 2, 3 ]  <--- we'll call this list1. It lives on the heap.

b = a             <- b now also points to list1.

b[1] = 5        <- This is a method call on the thing b points to, which of
course is the same thing as what a points to!

>>> a
[ 5, 2, 3]

Did this help?

-Chris