if you want spam and cheese to store two different listsyou have to create two different lists instead of copying referencespam [ cheese [ in the above examplespam and cheese have two different lists stored in them (even though these lists are identical in contentnow if you modify one of the listsit won' affect the other because spam and cheese have references to two different listsspam [ cheese [ cheese[ 'hello!spam [ cheese [ 'hello!' figure - shows how the two references point to two different lists figure - two variables each storing references to two different lists dictionaries also work the same way variables don' store dictionariesthey store references to dictionaries