How do I retain a new strings value during a loop, continuously changing the string until the loop ends?

Question

I want to take the value of a string and loop, asking the user to choose single character replacement during each loop iteration. I want to retain the changes the user makes to the string and then make an additional replacement which is also retained until the user chooses to end the loop.

newtext = ''
ciphertext = 'qsv el arm aepm sh tzz ussx pmb as dspm as arm tex sh armel dsvbaci.'
answer = 'y'

for letter in ciphertext:
    while answer is 'y':
        print(ciphertext)
        cl = input('Which letter would you like to replace? ')
        rl = input('What is the new letter? ')
        newtext += ciphertext.replace(cl,rl)
        print(newtext)
        answer = input('Would you like to continue? (y/n) ')

Answer 1

I think you should do like this:

original = 'qsv el arm aepm sh tzz ussx pmb as dspm as arm tex sh armel dsvbaci.'
ciphertext = 'qsv el arm aepm sh tzz ussx pmb as dspm as arm tex sh armel dsvbaci.'
newtext = ''
answer = 'y'


while answer is 'y':
    print(ciphertext)
    cl = raw_input('Which letter would you like to replace? ')
    rl = raw_input('What is the new letter? ')
    newtext = ciphertext.replace(cl,rl)
    print(newtext)
    answer = raw_input('Would you like to continue? (y/n) ')
    if(answer == "y"):
        ciphertext = newtext
    else:
        ciphertext = original

I changed a little bit your code. If you need any clarification lemme know

UPDATE

original = 'qsv el arm aepm sh tzz ussx pmb as dspm as arm tex sh armel dsvbaci.'
plaintext = 'qsv el arm aepm sh tzz ussx pmb as dspm as arm tex sh armel dsvbaci.'
answer = 'y'
replacements = {}


while answer is not 'q':
    print(plaintext)
    cl = input('Which letter would you like to replace? ')
    rl = input('What is the new letter? ')
    x = [i for i, ltr in enumerate(original) if ltr == cl]
    replacements[cl] = x
    plaintext = list(plaintext)
    for i in replacements[cl]:
        plaintext[i] = rl
    plaintext = "".join(plaintext)
    print plaintext
    answer = input('Would you like to continue? (y/n) ')
    if(answer == "n"):
        plaintext = original

This should be good! Lemme know. I'm aware about the raw_input problem, i changed to input for a faster "debugging". Sorry but i didn't understand before the problem correctly :P