Reference

[ast]

hello

Consider following code:

>>> A=7
>>> B=7
>>> A is B
True

I understand that there is a single object 7 somewhere in memory and
both variables A and B point toward this object 7

now do the same with a list:

>>> l1 = [1, 2]
>>> l2 = [1, 2]
>>> l1 is l2
False

It seems this time that there are 2 distincts objects [1, 2] in memory. l1 points
toward the first one and l2 points toward the second one.

if I change one, the second remains unchanged

>>> l1.append(3)
>>> l1
[1, 2, 3]
>>> l2
[1, 2]

I dont really understand why the behavior is different. 
Both integer 7 and list [1, 2] are objects. Why is it
different ?

thanks