[{'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:weather = weather.replace('M', np.NaN)\nweather = weather.replace('-', np.NaN)\nweather = weather.replace('T', 0.005) # very small amounts of rain can impact mosquito hatches\nweather.Tmax = weather.Tmax.fillna(method = 'ffill')\nweather.Tmin = weather.Tmin.fillna(method = 'ffill')\nweather.Depart = weather.Depart.fillna(method = 'ffill')\nweather.Heat = weather.Heat.fillna(method = 'ffill')\nweather.Cool = weather.Cool.fillna(method = 'ffill')\nweather.PrecipTotal = weather.PrecipTotal.fillna(method = 'ffill')"}, {'role': 'assistant', 'content': 'data_preprocessing'}]