df_test = pd.DataFrame(
    data=np.array([
        np.repeat(['class' + str(i+1) for i in range(2)], 10),
        list(range(10, 0, -1)) * 2,
        list(range(1, 11)) * 2
    ]).T,
    columns=['class'] + ['x'+str(i+1) for i in range(2)]
)  # np.array强制内部元素格式统一

df_test[df_test.columns.drop(['class'])] = df_test[df_test.columns.drop(['class'])].astype('int32')

df_test['y'] = df_test.apply(
    func=lambda x: 10 + np.exp(x['x1']) + np.exp(2 * x['x2']) + 10
        if x['class'] == 'class1'
        else (
            20 + np.exp(10 * x['x1']) + np.exp(-2 * x['x2']) - 10
            if x['class'] == 'class2'
            else np.nan
        ),
    axis=1
)

df_test