python - Addition of chars adding one character in front -

what i'm trying implement function increments string 1 character, example:

'aaa' + 1 = 'aab' 'aaz' + 1 = 'aba' 'zzz' + 1 = 'aaaa' 

i've implemented function first 2 cases, can't think of solution third case.

here's code :

def new_sku(s):     s = s[::-1]     already_added = false     new_sku = str()      in s:         if not already_added:             if (i < 'z'):                 already_added = true             new_sku += chr((ord(i)+1)%65%26 + 65)         else:             new_sku +=      return new_sku[::-1] 

any suggestions ?

how ?

def new_sku(s):     s = s[::-1]     already_added = false     new_sku = str()      in s:         if not already_added:             if (i < 'z'):                 already_added = true             new_sku += chr((ord(i)+1)%65%26 + 65)         else:             new_sku +=      if not already_added: # carry still left?         new_sku += 'a'      return new_sku[::-1] 

sample run :-

$ python sku.py z aa $ python sku.py zzz aaaa $ python sku.py aaa aab $ python sku.py aaz aba