[{'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:def null_percentage(column):\n    df_name = column.name\n    nans = np.count_nonzero(column.isnull().values)\n    total = column.size\n    frac = nans / total\n    perc = int(frac * 100)\n    print('%d%% of values or %d missing from %s column.' % (perc, nans, df_name))\n\ndef check_null(df, columns):\n    for col in columns:\n        null_percentage(df[col])\n        \ncheck_null(df, df.columns)"}, {'role': 'assistant', 'content': 'data_exploration'}]