python how to reassign dupilcate string values to a new string

• I take in a string aabullc

• newstring should be assigned aall after the loop since a and l are duplicates

• strings with more then 1 dupe like aaabullc should return aaall

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  def rearrangeLetters(S):
    print(len(S))
    start = 0
    newstring = ""
  
    for i in range(start+1, len(S)):
        if(S[start] == S[i]):
            newstring+=S[i]
            print(newstring)
            start +=1
  

issue:

print(newstring) is never running

>Solution :

Try this:

def rearrangeLetters(S):
    s = [S[i] for i in range(len(S))]
    newstring = ""
    for t in s:
        if s.count(t) > 1:
            
            newstring += t
    return newstring

call function:

output = rearrangeLetters("aabullc")
print(output)

output:

aall