I cannot import the cross_validation from sklearn library; I use sklearn version 0.20.0
from sklearn import cross_validation
later in the c
This happens because there is no cross_validation object in sklearn. You're likely looking for something more like the cross_validate function. You can access that through
from sklearn.model_selection import cross_validate
However, you don't need to import any cross-validation software to perform the train-test split, since that will just randomly sample from the data. Try
from sklearn.model_selection import train_test_split
followed by
features_train, features_test, labels_train, labels_test = train_test_split(word_data, authors, test_size=0.1, random_state=42)