Use Python function to change string "oalalaeah" to "hello"

Question

Hi I am learning python I was just trying to resolve the above example.That is make a function to change the string "oalalaeah" to "hello". Notice that 'hello' is the alternate letter starting from the back. I can do both individually. Important: I want to do it using only python functions()

`def rev_str(str1):
    new_str = ''
    index = len(str1)
    while index > 0:
        new_str += str1[index-1]
        index = index - 1
    return new_str`
print(rev_str('oalalaeah'))

to reverse the string to "haealalao"

later use:

def rev_alt(str2):
    fin_str = ''
    index = -2
    while index < len(str2)-1:
        fin_str += str2[index+2]
        index = index + 2
    return fin_str

print(rev_alt('haealalao'))

This gives me "hello" but these are 2 separate operations. I want to have 1 function that that will turn "oalalaeah" to "hello". I am sorry if this is too easy. Its driving me crazy

Why don't you create a third function rev_both() calling first rev_str() and then rev_alt()? — MEE, Feb 22 '18 at 16:28
i was going to comment you know he doesn't want the easy way lol — L_Church, Feb 22 '18 at 16:31
The only thing you need to change about your first function is to take every *second* letter instead of every letter… — deceze, Feb 22 '18 at 16:33
thanks +MEE I have been trying to do that. but it keeps giving me errors — Samir Tendulkar, Feb 22 '18 at 16:35
What exactly did you try and what errors is it giving you? Literally the only change needed is `1` → `2` in `index = index - 1`. — deceze, Feb 22 '18 at 16:36
@deceze It does not work I tried it. from the front counting starts from 0 from the back it starts from -1 not from 0 — Samir Tendulkar, Feb 22 '18 at 16:37

score 2 · Accepted Answer · answered Feb 22 '18 at 16:41

def rev_str(str1):
    new_str = ''
    index = len(str1)
    while index > 0:
        new_str += str1[index-1]
        index = index - 1
    return new_str

This is taking each letter in the string from the end to the beginning by decreasing the index by one on each iteration. Literally the only change needed to take every second letter is to decrease the index by two on each iteration:

def rev_str(str1):
    new_str = ''
    index = len(str1)
    while index > 0:
        new_str += str1[index-1]
        index = index - 2  #  here
    return new_str

print(rev_str('oalalaeah'))  # hello

The pythonic version of this is the built-in slice syntax:

print('oalalaeah'[::-2])  # hello

Thank you so thats what you do -1 the 1st time and -2 from the counter. Thanks — Samir Tendulkar, Feb 22 '18 at 16:45

Use Python function to change string "oalalaeah" to "hello"

1 Answers1