[{'role': 'system', 'content': "You are an expert in machine learning and your task is to classify code snippets into one of the following categories: ['helper_functions', 'load_data', 'data_exploration', 'data_preprocessing', 'evaluation', 'modelling', 'prediction', 'result_visualization', 'save_results', 'comment_only']."}, {'role': 'user', 'content': 'Identify the single most appropriate category to which the provided code belongs. Provide your response as a single category label without any additional information, commentary, or personal opinions.\\nPython Code:hide_code\nfrom sklearn.model_selection import ShuffleSplit\ndef fit_model(X, y):\n""" Performs grid search over the \'max_depth\' parameter for a\ndecision tree regressor trained on the input data [X, y]. """\ncv_sets = ShuffleSplit(n_splits = 10, test_size = 0.20, random_state = 0)\nregressor = DecisionTreeRegressor()\nparameters = {\'max_depth\': [1,2,3,4,5,6,7,8,9,10]}\nscoring_function = make_scorer(performance_metric)\ngrid = grid_search.GridSearchCV(regressor, parameters, scoring_function)\ngrid = grid.fit(X, y)\nreturn grid.best_estimator_'}, {'role': 'assistant', 'content': 'modelling'}]