I love using this visualization tool with students who are new to programming. You can create code snippets, and share them through a url.<p>Here is a quick example demonstrating why you need to use a slice to copy a list:<p><a href="http://pythontutor.com/visualize.html#code=my_foods+%3D+%5B'pizza',+'beer',+'steak+fries'%5D%0A%0A%23+Want+to+start+with+a+copy+of+my+list%3F%0A%23++Wrong+way%3A%0Ayour_foods+%3D+my_foods%0A%0A%23+Proof+that+it's+the+wrong+way%3A%0Ayour_foods.append('ice+cream')%0A%0A%0Amy_foods.remove('ice+cream')%0A%23+Proper+way+to+copy+my+list%3A%0Ayour_foods+%3D+my_foods%5B%3A%5D%0A%0A%23+Proof+that+we+have+separate+lists%3A%0Ayour_foods.append('ice_cream')&mode=display&cumulative=false&heapPrimitives=false&drawParentPointers=false&textReferences=false&showOnlyOutputs=false&py=3&curInstr=0" rel="nofollow">http://pythontutor.com/visualize.html#code=my_foods+%3D+%5B'...</a>