[noob question] References and copying

[Boris Borcic]

zefciu wrote:
> Hello!
> 
> Where can I find a good explanation when does an interpreter copy the
> value, and when does it create the reference.  I thought I understand
> it, but I have just typed in following commands:
> 
>>>> a=[[1,2],[3,4]]
>>>> b=a[1]
>>>> b=[5,6]
>>>> a
> [[1, 2], [3, 4]]
>>>> b
> [5, 6]
> 
> And I don't understand it.  I thought, that b will be a reference to a,
> so changing b should change a as well.

It would if you had written "b[:]=[5,6]"

> What do I do wrong.  And a
> second question - can I create a reference to element of a list of
> floating points and use this reference to change that element?

not like that.

> 
> Greets to all PyFans
> zefciu