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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def excel_key(index):
 """create a key for index by converting index into a base-26 number, using A-Z as the characters."""

    X = lambda n: ~n and X((n // 26)-1) + chr(65 + (n % 26)) or ''
    return X(int(index))