"Ben C" wrote:
> I used to think it assigned with things like integers, because if you
> write:
>
> a = 5
> b = a
> b += 1
> print a
>
> a is still 5. So it looked like a and b stored values and b got a "copy"
> of a's value. But this is the wrong interpretation,
>
> b += 1
>
> is really b = b + 1, and rebinds b.
almost: "b += obj" is really "b = b.__iadd__(obj)" with "b = b + obj"
as a fallback if __iadd__ isn't supported by "b".
> If it weren't for the id() function I think the difference between
> "variable stores value", "variable stores immutable reference" and
> "variable stores copy-on-write reference" would be implementation
> detail and never visible to the programmer.
except when they are:
>>> a = [1, 2, 3]
>>> b = a
>>> b += [4]
>>> a
[1, 2, 3, 4]
>>> b
[1, 2, 3, 4]
</F>
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