Please help understand this code

Question

I don't understand the output of this code :
A = [1,2,3,[6,7,8,9]]
B = A[:]
A[1] = 4
A[3][1] = 0
print(B)
why is it [1,2,3,[6,0,8,9]] and not [1,4,3,[6,0,8,9]] ?

Answer 1

B is a copy of A. not a reference
you can make it a copy by removing the [:]

Answer 2

Ok but why the list inside A has changed ?

Answer 3

...cause you changed the values...