36日目最初の重複しない文字

def first_non_repeating_letter(string):
    trans = string.lower()
    arr = []
    for i in range(0, trans.__len__()-1):
        for j in range(i+1, trans.__len__()):
            if trans[i] == trans[j]:
                arr.append(i)
                arr.append(j)
                print(i, j)
    arr = list(set(arr))
    to_result = []
    for i in range(0, len(string)):
        to_result.append(string[i])
    for i in range(0, arr.__len__()):
        to_result[arr[i]] = 'del'
    while 'del' in to_result:
        to_result.remove('del')
    if not to_result:
        result = ''
    else:
        result = to_result[0]
    return result