When I copy code in List 5.1 and run in jupyter, it always tells me this: >Can't get attribute 'square' on <module '__main__' (built-in)> According to what I have found in Google, it seems that the code needs to be titled: > if __name__ =='__main__': but this way only works in Spyder and Pycharm. So I wanna know how you guys tackle it. Grateful to hear any suggestions!