Python list updating itself

Question

Well this is kind of an elementary question, but here it goes:

Consider the following code:

listA = ['a','b','c']
listB = listA
listB.pop(0)
print listB
print listA

The output comes as:

['b','c']
['b','c']

However, shouldn't the output be:

['b','c']
['a','b','c']

What exactly is happening here? And how could I get the expected output? Thanks in advance :)

Answer 1

The variable listB is nothing but a reference to listA. If you want a copy of listA you can issue

listB = listA[:] 

for a shallow copy or

import copy
listB = copy.deepcopy(listA)

for a deep copy. Here is a good read on the topic.