def get_skewness(df, col):
    """
    Exclude outer 3% data
    :param df: a dataframe
    :param col: column name, must be numerical
    :return: skewness
    """
    q_015, q_985 = df[col].quantile([0.015, 0.985])
    return df[col][(col >= q_015) & (col <= q_985)].skew()