title: Python stops working when using weight class in fitting of XGBoost
body: <p>I'm dealing with hight imbalanced data in a classification problem, so I use a weighted class in order to deal with this issue,
  but Python stops working when I just run this Jupyter notebook cell (the fitting cell). </p>
  
  <p>My code:</p>
  
  <pre><code>xg = XGBClassifier(objective ='reg:logistic', colsample_bytree = 0.3, learning_rate = 0.01,
              max_depth = 5, alpha = 10, n_estimators = 100)
  
  class_weight = {0: 1,
              1: 9}
  
  xg.fit(X_train,y_train,sample_weight=class_weight)
  </code></pre>