Can someone explain this to me

Question

https://code.sololearn.com/cVBN3xITcwcp/?ref=app

Answer 1

For ex:
str = "a", i = "b'
1) str += I => str = str + i = "a" + "b" = "ab"; #its appending , but later one is prepending,
2) str = i + str => "b" + "a" = "ba"