Python使用递归函数或其他方法简化嵌套for循环

nested_list = [1, [2, [3, 4], 5], 6]
flat_list = []

for item in nested_list:
    if isinstance(item, list):
        for sub_item in item:
            if isinstance(sub_item, list):
                for sub_sub_item in sub_item:
                    flat_list.append(sub_sub_item)
            else:
                flat_list.append(sub_item)
    else:
        flat_list.append(item)

print(flat_list)  # 输出: [1, 2, 3, 4, 5, 6]

def flatten(nested_list):
    flat_list = []
    for item in nested_list:
        if isinstance(item, list):
            flat_list.extend(flatten(item))
        else:
            flat_list.append(item)
    return flat_list

nested_list = [1, [2, [3, 4], 5], 6]
flat_list = flatten(nested_list)
print(flat_list)  # 输出: [1, 2, 3, 4, 5, 6]