What is this class representation [3 3 3 0 3 3 3 3 2 0]?

They are printing the first 10 elements of y_train, which is a vector containing the “labels” on the 100 input data samples. Since there are 4 possible label values representing the 4 different classes, all the values are 0 through 3. So the first three samples are all in the category 3, whatever that represents here. The fourth sample is of class 0. And so forth …