=====Problem Statement=====
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 changes to it.
Task
Read a given string, change the character at a given index and then print the modified string. 
=====Example=====
Example
>>> string = "abracadabra"
You can access an index by:
>>> print string[5]
a
What if you would like to assign a value?
>>> string[5] = 'k' 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'str' object does not support item assignment
How would you approach this?
    One solution is to convert the string to a list and then change the value.
Example
>>> string = "abracadabra"
>>> l = list(string)
>>> l[5] = 'k'
>>> string = ''.join(l)
>>> print string
abrackdabra
    Another approach is to slice the string and join it back.
Example
>>> string = string[:5] + "k" + string[6:]
>>> print string
abrackdabra
=====Input Format=====
The first line contains a string, S.
The next line contains an integer i, denoting the index location and a character c separated by a space.
=====Output Format=====
Using any of the methods explained above, replace the character at index i with character c.
def mutate_string(string, position, character):
    out = list(string)
    out[position] = character
    return "".join(out)
def mutate_string(string, position, character):
    out = list(string)
    out[position] = character
    return "".join(out)