insert()是Python中的内置函数，可将给定元素插入列表中的给定索引。
用法:
list_name.insert(index， element)
参数：
index - the index at which the element has to be inserted.
element - the element to be inserted in the list.
返回值：
This method does not return any value but
it inserts the given element at the given index.
