s = 'abcabcabc'
 i = 0
 j = 1
 longestSubString = ''
 realString = ''
 while (j < len(s)):
    if i == 0:
        longestSubString = s[i]
    if (s[j] >= s[i]):
        longestSubString = longestSubString + s[i]
        if len(longestSubString) > len (realString):
            realString = longestSubString
        i += 1
        j += 1
    else:
        longestSubString = ''
        i += 1
        j += 1
print ("Longest SubString is: " + realString)

import string

s = 'azcbobobegghakl'
i = 0
currentSubString = ''
longestSubString = ''

while (i < len(s)):

    positionCurrent = string.ascii_lowercase.index(s[i])
    positionPrevious = string.ascii_lowercase.index(s[i-1])
    currentCharacter = s[i]
    i += 1

    if (positionCurrent != positionPrevious + 1):
        currentSubString = ''

    currentSubString += currentCharacter

    if len(longestSubString) < len(currentSubString):
        longestSubString = currentSubString

print("Longest SubString is: " + longestSubString)

s = 'azcbobobegghakl'
res = ''
tmp = ''

for i in range(len(s)):
    tmp += s[i]
    if len(tmp) > len(res):
        res = tmp
    if i > len(s)-2:
        break
    if s[i] > s[i+1]:
        tmp = ''

print("Longest substring in alphabetical order is: {}".format(res))