문장에서 old를 new 로 바꾸는건데
풀긴 풀었는데 이해가 안가서..
i=len(sentence)-len(old) 이부분을 원래 i=sentence - old로 썼다가
에러나서 이것저것 고치다가 len넣으니까 되서 일단 저렇게 바꿨는데
len은 몇글자인지 나타내는거잖아
근데 이게 왜 돼?


The replace_ending function replaces the old string in a sentence with the new string, but only if the sentence ends with the old string. If there is more than one occurrence of the old string in the sentence, only the one at the end is replaced, not all of them. For example, replace_ending("abcabc", "abc", "xyz") should return abcxyz, not xyzxyz or xyzabc. The string comparison is case-sensitive, so replace_ending("abcabc", "ABC", "xyz") should return abcabc (no changes made).

def replace_ending(sentence, old, new):
    # Check if the old string is at the end of the sentence 
    if sentence.endswith(old):
        # Using i as the slicing index, combine the part
        # of the sentence up to the matched string at the 
        # end with the new string
        i=len(sentence)-len(old)
        new_sentence = sentence[:i]+new
        return new_sentence

    # Return the original sentence if there is no match 
    return sentence
    
print(replace_ending("It's raining cats and cats", "cats", "dogs")) 
# Should display "It's raining cats and dogs"
print(replace_ending("She sells seashells by the seashore", "seashells", "donuts")) 
# Should display "She sells seashells by the seashore"
print(replace_ending("The weather is nice in May", "may", "april")) 
# Should display "The weather is nice in May"
print(replace_ending("The weather is nice in May", "May", "April")) 
# Should display "The weather is nice in April"