On 2015-01-02 13:57, Steven D'Aprano wrote:
On Fri, Jan 02, 2015 at 09:57:29AM -0800, Alex Kleider wrote:
On 2015-01-01 17:35, Alan Gauld wrote:
>Repeats replicates the reference to the object but
>does not create a new object.
This part I can understand but, as Steven has pointed out,
this behaviour changes if the object being repeated is immutable.
Why would one get a new object (rather than a new reference to it)
just because it is immutable? It's this difference in behaviour
that depends on mutability that I still don't understand even though
Steven did try to explain it to me:
"""
If the list items are immutable, like ints or strings, the difference
doesn't matter. You can't modify immutable objects in-place, so you
never notice any difference between copying them or not.
"""
No, you misunderstood what I was trying to say.
Yes, Steven, I did but you've set that straight and
I thank you for it. Here's what finally helped me figure
it out:
a = [{}, 999]
b = a*3
b
[{}, 999, {}, 999, {}, 999]
b[2] = 'hello'
b
[{}, 999, 'hello', 999, {}, 999]
b[4]["a"] = 1
b
[{'a': 1}, 999, 'hello', 999, {'a': 1}, 999]
b[4] = 1
b
[{'a': 1}, 999, 'hello', 999, 1, 999]
Again, my compliments to this list for the admirable way it
fulfils its mission!
Alex
But with immutable objects, there is nothing you can do (except check
the IDs) that will reveal the difference between having one or two
distinct objects:
a = 123
b = 123
*may or may not* set a and b to distinct objects. Because when it comes
to immutable objects, it makes no difference.
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