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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 _col_name(index):
 """ Converts a column index to a column name. 'A' 'AA' """

    for exp in itertools.count(1):
        limit = 26 ** exp
        if index < limit:
            return ''.join(chr(ord('A') + index // (26 ** i) % 26) for i in range(exp-1, -1, -1))
        index -= limit