Find the longest upsequence in a string

def longuest_upsequence(s):
        lg_start_index = 0
        lg_size = 1
        current_size = 0
        current_index = 0
        for i in range (0 , len(s) - 1):
                if s[i] < s[i+1]:
                        if current_size > lg_size:
                                lg_start_index = current_index
                                lg_size = current_size
                        curent_index = i
                        current_size = 1
                else:
                        current_size++