Python sort() prints correct value but array isn't sorted

Question

input is

[1,2,3,0,0,0]
3
[2,5,6]
3

Code is

def merge(self, nums1: List[int], m: int, nums2: List[int], n: int) -> None:
    nums1 = nums1[0:m] + nums2[0:n]
    nums1.sort()
    print(nums1)

stdout is

[1, 2, 2, 3, 5, 6]

But, array is

[1,2,3,0,0,0]

Why is this the case?

I thought the array would be [1, 2, 2, 3, 5, 6] as well