HackerRank Python Solution - Strings - Mutations

  • 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.
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
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, 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
Solution:

def mutate_string(string, position, character):
    
    string_list = list(string)
    string_list[position]=character
    return ''.join(string_list)

if __name__ == '__main__':
    s = input()
    i, c = input().split()
    s_new = mutate_string(s, int(i), c)
    print(s_new)
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