Deep copy Python with integers vs arrays

Question

Given the following code:

x = y = z = 0
x = 10
print(y) // prints 0

x = y = z = [1, 2, 3, 4, 5]
x[0] = 10
print(y) // prints [10, 2, 3, 4, 5]

How come with simple integers Python does not perform a deep copy whilst with arrays it does?

Answer 1

In the first example, you have three pointers pointing to a memory location for an integer. Then you direct one of the pointers, X, to a different memory location. The other two pointers continue to point to the original integer. In the second example, you have three pointers pointing to a list. The list is mutable. Then you change one of the items in the list. The three-pointers are still pointing to the same list and checking the value of any of them will return the same answer.