我试图执行代码，但问题显示为“Name 'X' is not defined”“如果没有，我如何定义它以使代码运行。

from sklearn.model_selection import train_test_split

X_train, X_test, y_train, y_test = train_test_split(X, y, test_size = 0.2, random_state = 42)


todo_check([
    (X_train.shape == (413, 29), 'X_train does not have the correct shape (413, 29)'),
    (X_test.shape == (104, 29), 'X_test does not have the correct shape (104, 29)'),
    (y_train.shape == (413,), 'y_train does not have the correct shape (413,)'),
    (y_test.shape == (104,), 'y_test does not have the correct shape (104,)'),
    (np.all(np.isclose(X_train.values[-5:, -4], np.array([17.7, 18.2, 21.8, 23.8, 20.1]),rtol=.01)), 'X_train does not contain the correct values! Make sure you used `X` when splitting!'),
    (np.all(np.isclose(y_test.values[-5:], np.array([1.25561604, 1.8531681 , 1.15373159, 4.01259206, 3.56558124]),rtol=.01)), 'y_test does not have the correct values! Make sure you used `y` when splitting!')
])

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我希望代码能够完整地构造并找出X未定义的原因以及如何编译它