str = ‘Amit Upadhyay’
It requires calling a string method
str.join on another called function, which canbe rather slow.
def reverseString (str): newStr = "" index = len(str) while index: index -= 1 newStr += str[index] return newStr; print reverseString("Amit Upadhyay")
This is bad because strings are immutable. So every time you are appending a new character, which is creating a new string. So it is better to collect your substring in a list and join them later. This moves us to the approach 4.
def reverseString (str): newList =  index = len(str) while index: index -= 1 newList.append(str[index]) return "".join(newList); print reverseString("Amit Upadhyay")
Thank you 👏