title: GridSearchCV' object has no attribute 'best_score_'
body: <pre><code># create a grid of parameters to search (and specify the pipeline step along with the parameter)
  param_grid = {}
  param_grid['countvectorizer__token_pattern'] = [r"\b\w\w+\b", r"'([a-z ]+)'"]
  param_grid['multinomialnb__alpha'] = [0.5, 1]
  param_grid
  
  # pass the pipeline (instead of the model) to GridSearchCV and measuring the accuracy of the model
  from sklearn.model_selection import GridSearchCV
  grid = GridSearchCV(pipe, param_grid, cv=5, scoring='accuracy')
  
  # time the grid search
  %time grid.fit(X, y)
  
  # print the single best score and parameters that produced that score
  print(grid.best_score_)
  print(grid.best_params_)
  </code></pre>
  
  <p>this is the error: </p>
  
  <p><em>GridSearchCV' object has no attribute 'best_score_'</em></p>
  
  <p>How I can address it?</p>