def GetExcelStyleColumnLabel(ColNum):
    """Return Excel style column label for a colum number.
    
    Arguments:
        ColNum (int): Column number

    Returns:
        str : Excel style column label.

    """
    Letters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
    
    ColLabelList = []
    while ColNum:
        ColNum, SubColNum = divmod(ColNum - 1, 26)
        ColLabelList[:0] = Letters[SubColNum]
    
    return ''.join(ColLabelList)