join

1

def solution(my_string, index_list):
    answer = ''
    for i in index_list:
        answer += my_string[i]
    return answer

 

 

2

def solution(my_string, index_list):
    return ''.join([my_string[i] for i in index_list])

*1 대신 2 사용

 

3

def solution(my_string):
    answer = ''
    for i in my_string:
        if i.islower():
            answer += i.upper()
        else:
            answer += i.lower()

    return answer

 

4

def solution(my_string):
    return ''.join([i.lower() if i.isupper() else i.upper() for i in my_string])

*3 대신 4 사용