TypeError: slice indices must be integers

[syakesaba]

 19 validation_num = x_train.shape[0] * validation_rate
 20 x_train, t_train = shuffle_dataset(x_train, t_train)

---> 21 x_val = x_train[:validation_num] 22 t_val = t_train[:validation_num] 23 x_train = x_train[validation_num:]

TypeError: slice indices must be integers or None or have an index method