如何在mergeSort中将无限表示为前哨卡片？

def mergeSort(arr, sentinel):
    if len(arr) <= 1:
        return arr
    
    mid = len(arr) // 2
    left = mergeSort(arr[:mid], sentinel)
    right = mergeSort(arr[mid:], sentinel)
    
    return merge(left, right, sentinel)

def merge(left, right, sentinel):
    result = []
    i = j = 0
    
    while i < len(left) and j < len(right):
        if left[i] <= right[j]:
            result.append(left[i])
            i += 1
        else:
            result.append(right[j])
            j += 1
    
    while i < len(left):
        result.append(left[i])
        i += 1
    
    while j < len(right):
        result.append(right[j])
        j += 1
    
    return result

arr = [5, 3, 8, 2, 1, 9, 4]
sentinel = float('inf')
sorted_arr = mergeSort(arr, sentinel)
print(sorted_arr)