python合并排序实现错误:超过最大递归深度

def merge_sort(arr):
    if len(arr) <= 1:
        return arr
    
    # 将待排序序列划分成较小的子序列
    sublists = [[x] for x in arr]
    
    # 逐步合并子序列
    while len(sublists) > 1:
        new_sublists = []
        for i in range(0, len(sublists)-1, 2):
            merged = merge(sublists[i], sublists[i+1])
            new_sublists.append(merged)
        if len(sublists) % 2 == 1:
            new_sublists.append(sublists[-1])
        sublists = new_sublists
    
    return sublists[0]

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