Simple del[] list question

[Matthew Hirsch]

Hi All,

What is going on here?

This leaves a intact.

>>> a=[[1,2,3],[4,5,6]]
>>> b=a[:]
>>> del b[0]
>>> b
[[4, 5, 6]]
>>> a
[[1, 2, 3], [4, 5, 6]]


This also changes a.

>>> a=[[1,2,3],[4,5,6]]
>>> b=a[:]
>>> del b[0][0]
>>> b
[[2, 3], [4, 5, 6]]
>>> a
[[2, 3], [4, 5, 6]]

Why did a change?  Why suddenly when you go to two dimensions does the 
behavior change?

Thanks,
Matt