[{'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 random_portfolio(returns):\n'''\nReturns the means and std of returns for a random portfolio\n'''\np = np.asmatrix(np.mean(returns, axis=1))\nw = np.asmatrix(rand_weights(returns.shape[0]))\nC = np.asmatrix(np.cov(returns))\nmu = w*p.T\nsigma = np.sqrt(w*C*w.T)\nif sigma > 2:\nreturn random_portfolio(returns)\nreturn mu, sigma"}, {'role': 'assistant', 'content': 'modelling'}]