Solution Exercise 19

Define a function reverse() that computes the reversal of a string. For example, reverse("I am testing") should return the string "gnitset ma I".

def reverse(inStr):
    newStr = ""
    #As we want to use the index operator [] to
    #pick a character from the original str (inStr)
    #we want the range to move backwards from the 
    #last character to the first.
    #The last character in inStr has the index value of len(inStr) -1
    #We need -1 as len returns the number of characters found in inStr
    #but the index starts at 0.
    #The secons -1 in the range is there because we want to end the range at the value
    #before -1, that is 0, the index value of the first character in inStr.
    #The last -1 is so the range will decreese its values by one each time.
    for i in range(len(inStr)-1,-1,-1):
        #Append this character into newStr
        newStr += inStr[i]
    return newStr

def main():
    print(reverse("I am testing"))
    
if __name__ == '__main__':
    main()

Note! There are simpler ways to reverse a string but as this is an easy exercise this solution is sufficient.