@classmethod
def _get_sma(cls, df, column, windows):
    """ get simple moving average

        :param df: data
        :param column: column to calculate
        :param windows: collection of window of simple moving average
        :return: None
        """
    window = cls.get_only_one_positive_int(windows)
    column_name = '{}_{}_sma'.format(column, window)
    df[column_name] = df[column].rolling(min_periods=1, window=window,
        center=False).mean()
