[{'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:true_sigma = 2.0 # The true (unknown) value of the standard deviation, sigma\nnum_samples = 500\ndata = np.random.normal(scale=true_sigma, size=num_samples)\nsigma = pm.Exponential("sigma", beta=0.01)\n@pm.deterministic\ndef tau(sigma=sigma):\nreturn 1.0 / sigma**2\nobservations = pm.Normal("obs", 0, tau, value=data, observed=True)\nmodel = pm.Model([sigma, observations])'}, {'role': 'assistant', 'content': "['modelling']"}]