Stratified K-fold

# Import StratifiedKFold
from sklearn.model_selection import StratifiedKFold

# Create a StratifiedKFold object
str_kf = ____(n_splits=____, shuffle=____, random_state=123)

# Loop through each split
fold = 0
for train_index, test_index in ____.____(train, train['interest_level']):
    # Obtain training and testing folds
    cv_train, cv_test = ____.iloc[____], ____.iloc[____]
    print('Fold: {}'.format(fold))
    print('CV train shape: {}'.format(cv_train.shape))
    print('Medium interest listings in CV train: {}\n'.format(sum(cv_train.interest_level == 'medium')))
    fold += 1