Increment a String by 1 character in for loop (Python 3)

Question

Let's say I have an input string str and I want to increase it's value by 1 digit each loop so 'a'->'b' & 'm'->'n', and when it reaches 'z' it increases as shown in the example below.

str= "aaaaa"
output= "aaaab"

str="aaaaz"
output="aaaba"

str ="kbzzz"
output="kcaaa"

I hope you get the idea, it is sort of like a car's odometer. How to implement this function?

user2390182 · Accepted Answer · 2021-11-03 13:16:08Z

2

A simple approach (using a for-else loop):

def increment(s):
    for i in range(len(s)-1, -1, -1):
        if s[i] != "z":
            break
    else:
        return "a" * (len(s) + 1)
    return s[:i] + chr(ord(s[i]) + 1) + "a" * (len(s) - i - 1)

>>> increment("aaaaa")
'aaaab'
>>> increment("aaaab")
'aaaac'
>>> increment("aazz")
'abaa'

go through the string from the back
stop at the first non-"z"
if no non-"z" is found, return all "a" (increase length)
otherwise increment the non-"z" and reset the suffix to all "a"s

Some documentation:

edited Nov 3, 2021 at 13:16

answered Nov 3, 2021 at 12:48

user2390182

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