How to solve Python Memory Error ?. While loop does not stop running

this code is to find a subset of a string, which has unique characters.
make k parts of the string and t then print these parts while not includeing the same character in the string

    def merge_the_tools(string, k):
        l = len(string)
        start = 0
        t = []
        ans = []
        while True:
            put=''

            for i in range(start,start+k):
                put += string[i]

            start = k
            t.append(put)
            if start + k == l:
                break

        for i in t:
            ss = set(i)
            s = ''
            for j in ss:
                s += j 

            ans.append(s)
            for i  in s:
                print(I)
   merge_the_tools('AABBAACC',2)

I think there is a problem with ,while loop which I’m not able to find.