def fill_na(df):
    for col in df.columns:
        if (('_lag_' in col) & df[col].isnull().any()):
            if ('item_cnt' in col):
                df[col].fillna(0, inplace=True)
            if ('shop_mean' in col):
                df[col].fillna(0, inplace=True)
            if ('average_item_price' in col):
                df[col].fillna(0, inplace=True)
    return df
def fill_na(df):
    for col in df.columns:
        if (('_lag_' in col) & df[col].isnull().any()):
            if ('item_cnt' in col):
                df[col].fillna(0, inplace=True)
            if ('shop_mean' in col):
                df[col].fillna(0, inplace=True)
            if ('average_item_price' in col):
                df[col].fillna(0, inplace=True)
    return df