Is Python list variable not passing by reference?

Question

I'm confused with the pass-by-ref and pass-by-value in Python. In the following code, when listB = listA, listB should being assigned the pointer (reference) to the list in ListA variable. Any changes to listB should be reflected on listA. However, that is not the case in my test. Am I doing something wrong with the code? I'm running Python 3.4.3

>>> listA = [1,2,3]
>>> listB = listA
>>> listA = [4,5,6]
>>> print(listA, listB)
[4, 5, 6] [1, 2, 3]
>>> listB[0] ='new'
>>> print(listA, listB)
[4, 5, 6] ['new', 2, 3]

Answer 1

You're reassigning listA altogether, so there is no relation between it and listB.

For example:

listA = [2,2,3]

listB = listA

id(listA)
Out[6]: 90404936

id(listB)
Out[7]: 90404936

listA[0]=2

id(listA)
Out[9]: 90404936

listB
Out[10]: [2, 2, 3]

But then when you reassign listA you lose that id:

listA = [3,3,3]

id(listA)
Out[12]: 92762056

But listB stays at the same id:

id(listB)
Out[13]: 90404936