Iterative Merge Sort in Python

iterative_merge_sort.py

def merge(arr, i, mid, j, extra):
    x = i
    y = mid
    while x < mid and y < j:
        if arr[x] <= arr[y]:
            extra[x + y - mid] = arr[x]
            x += 1
        else:
            extra[x + y - mid] = arr[y]
            y += 1
    extra[x + y - mid : y] = arr[x : mid]
    extra[y : j] = arr[y : j]
    arr[i : j] = extra[i : j]

def sort(arr):
    n = len(arr)
    k = len("{:0b}".format(n))
    pad = pow(2, k) - n
    arr.extend([float('inf')] * pad)
    extra = [0] * (n + pad)
    l = 1
    for _ in range(k):
        for i in range(0, n + pad, 2 * l):
            merge(arr, i, i + l, i + 2 * l, extra)
        l *= 2
    del arr[-pad:]
        
arr = [5, 4, 3, 2, 1]
sort(arr)
print(arr)