a simple example: >>> basket = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana'] >>> fruits = set(basket) # create a set without duplicates a error raise: >>> basket = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana'] >>> fruits = set(basket) IronPython.Objects.PythonNameError: name 'set' is not defined at input_6.Run(Frame frame)