[{'role': 'system', 'content': "You are an expert in machine learning and your task is to classify the code snippets into categories from the provided list of categories. List of categories: ['helper_functions', 'load_data', 'data_exploration', 'data_preprocessing', 'evaluation', 'modelling', 'prediction', 'result_visualization', 'save_results', 'comment_only']"}, {'role': 'user', 'content': "Identify to which category the provided code belongs and assign the code snippet to at least 1 but up to 5 categories based on the probabilities, ignore if the probability of the category is negligible. Strictly provide your response as a list. Avoid providing any additional information, commentary, or personal opinions.\\nPython Code:sd = SingleStockDaily\ndf = pd.read_sql(session.query(sd.openingprice,sd.closingtprice,sd.avg5d,sd.avg10d,sd.avg20d,sd.avg60d,sd.tradeDate,sd.tradeVolume)\\\n.order_by(sd.tradeDate).filter(sd.stockid=='1215').statement, session.bind)\ndf['pricediff'] = np.nan\nfor i in range(len(df)-1,0,-1):\ndf.loc[i-1, 'pricediff']=df.loc[i, 'closingtprice']-df.loc[i-1, 'closingtprice']"}, {'role': 'assistant', 'content': "['data_preprocessing']"}]