An interesting exercise from __Rapid GUI Programming with Python and Qt__

incrementString.py

# vim: set fileencoding=utf-8:

def incrementString(char):
  if char.isalpha():
    char = char.upper()
  else:
    raise ValueError

  char_len = len(char)
  ord_list = [ord(s) for s in reversed(char)]

  for i in range(char_len):
    o = ord_list[i]
    if (o + 1) <= 90:
      ord_list[i] += 1
      break
    else:
      ord_list[i] = 65
      if (i + 1) == char_len:
        ord_list.append(65)
        break

  char = ''.join([chr(s) for s in reversed(ord_list)])
  return char


if __name__ == '__main__':
  print(incrementString('A'))
  print(incrementString('Z'))
  print(incrementString('AM'))
  print(incrementString('AZ'))
  print(incrementString('BA'))
  print(incrementString('BZ'))
  print(incrementString('ZZA'))
  print(incrementString('ZZZ'))
  print(incrementString('AAAA'))
  print(incrementString('AAAZ'))
  print(incrementString('ABC2'))