一、题目

We have seen that lists are mutable (they can be changed), and tuples are immutable (they cannot be changed).

Let's try to understand this with an example.

You are given an immutable string, and you want to make chaneges to it.

Example

>>> sting = "abracadabra"

You can access an index by :

>>> print string[5]

a

What if you would like to assign a value?

>>> sting[5] = 'k'

Traceback (most recent call last):

  File "", line 1, in

TypeError: 'str' object does not support item assigment

How would you approach this?

* One solution is to convert the string to a list and then change the value.

Example

>>> stirng = "abracadabra"

>>> a = list(string)

>>> a[5] = 'k'

>>> string = ''.join(a)

abrackdabra

* Aanother approach is to slice the string and join it back.

Example

>>> string = string[:5] + "k" + string[6:]

>>> print string

abrackdabra

Task

Read a given string, change the character at a given index and then print the modified string.

Function Description

Complete the mutate_string function in the editor below.

mutate_string has the following parameters:
* string string : the string to change

* int position: the index to insert the character at 

* string character: the character to insert

Returns

* string: the altered string

Input Format

The first line contains a string.

The next line contains an integer position, the index location and a string character, separated by a space.

Sample Input

STDIN                Function

------                    -----------

abracadabra       s = 'abracadabra'

5  k                      position = 5 , character = 'k'

Sample Output

abrackdabra

二、代码

def mutate_string(string, position, character):     a = list(string)     a[position] = character     string = ''.join(a)     return string  if __name__ == '__main__':     s = input()     i, c = input().split()     s_new = mutate_string(s, int(i), c)     print(s_new)

三、解读

元组（tuple）在Python中是不可变数据类型，这意味着一旦创建，就不能更改其内容，包括不能添加、删除或修改元组中的元素。

元组的不可变特性

• 不能更改元素：你不能给元组的某个元素赋新的值。
• 不能添加或删除元素：你不能在元组中添加新元素或删除现有元素。

直接赋值

虽然不能修改元组中的元素，但你可以通过以下方式“重新赋值”：

1. 重新创建：创建一个新的元组，并赋予相同的变量名。
2. 切片和连接：通过组合现有元组的部分元素和新元素来创建新元组。

示例：

# 创建一个元组 t = (1, 2, 3)  # 尝试修改元组中的元素（这将引发TypeError） try:     t[1] = 20 except TypeError as e:     print(e)  # 输出错误信息  # 创建一个新的元组，并赋予相同的变量名 t = (1, 20 ,3) print(t)  # 输出：（1, 20, 3）  # 使用切片和连接创建一个新元组 t = t[:1] + (20,) + t[2:] print(t) # 输出：(1, 20, 3) 

• 尝试修改元组的操作会引发一个TypeError，因为元组是不可变的。
• 通过重新创建一个新的元组并赋予相同的变量名，可以“替换”原来的元组。
• 使用切片和连接的方式也可以创建一个新的元组，这种方式在处理大量数据时更为高效。

总之，虽然元组不可变，但可以通过创建新元组的方式来实现“赋新值”的效果。