Finding longest substring in alphabetical order

Question

EDIT: I am aware that a question with similar task was already asked in SO but I\'m interested to find out the problem in this specific piece of code. I am

Answer 1

s = 'azcbobobegghakl' 

i=1
subs=s[0]
subs2=s[0]
while(i=s[j-1]):
            subs+=s[j]
            j+=1 
        else:
            subs=subs.replace(subs[:len(subs)],s[i])   
            break

        if(len(subs)>len(subs2)):
            subs2=subs2.replace(subs2[:len(subs2)], subs[:len(subs)])
    subs=subs.replace(subs[:len(subs)],s[i])
    i+=1
print("Longest substring in alphabetical order is:",subs2)