Reverse-replacing the first letter of each word with the letter of the previous word

Question

I've written a function that takes a message (string) as an input and replaces the first letter of each word with the first letter of the previous word (for the very first word, I take the first letter of the last word):

def changeFirst(message):
    msg_list=list(message)
    j=0
    pre=msg_list[j]
    for i in range(len(msg_list)):
        if msg_list[i]==' ':
            nextpre=msg_list[i+1]
            msg_list[i+1]=pre
            pre=nextpre
    msg_list[0]=pre
    msg_list=''.join(msg_list)
    return msg_list

changeFirst("now you are in love with me")
mow nou yre an iove lith we

I want to write a funtion UnchangeFirst() which reverses this function, for example it should work like this:

UnchangeFirst("mow nou yre an iove lith we")
now you are in love with me

How can I reverse this function?

Answer 1

Here it is!

def changedAgain(message2):
    msg_list = list(message2)
    j = 0
    first=msg_list[0]
    for i in range(len(msg_list)):
        if msg_list[i]==' ':
            msg_list[j]=msg_list[i+1]
            msg_list[i+1]=msg_list[j]
            j=i+1

    msg_list[j]=first
    return(''.join(msg_list))

message2="mow nou yre an iove lith we"

print(changedAgain(message2))
>>> "now you are in love with me"