def sma(df, s, period, column):
    """Gets simple moving average

    Args:
        df (DataFrame): data
        s (slice): the slice object
        period (int): size of the moving period
        column (str): column name to calculate

    Returns:
        pandas.Series
    """
    return df[column][s].rolling(min_periods=period, window=period, center=
        False).mean(), period
