indexon the other handjust stores reference to the empty list object in the specified slotrather than deleting an iteml ['already''got''one' [ :[ ['already' [ [ [[]although all the operations just discussed are typicalthere may be additional list methods and operations not illustrated here the method setfor examplemay change over timeand in fact has in python --its new copy(method makes top-level copy of the listmuch like [:and list( )but is symmetric with copy in sets and dictionaries for comprehensive and up-to-date list of type toolsyou should always consult python' manualspython' dir and help functions (which we first met in )or one of the reference texts mentioned in the preface and because it' such common hurdlei' also like to remind you again that all the in-place change operations discussed here work only for mutable objectsthey won' work on strings (or tuplesdiscussed in )no matter how hard you try mutability is an inherent property of each object type dictionaries along with listsdictionaries are one of the most flexible built-in data types in python if you think of lists as ordered collections of objectsyou can think of dictionaries as unordered collectionsthe chief distinction is that in dictionariesitems are stored and fetched by keyinstead of by positional offset while lists can serve roles similar to arrays in other languagesdictionaries take the place of recordssearch tablesand any other sort of aggregation where item names are more meaningful than item positions for exampledictionaries can replace many of the searching algorithms and data structures you might have to implement manually in lower-level languages--as highly optimized built-in typeindexing dictionary is very fast search operation dictionaries also sometimes do the work of recordsstructsand symbol tables used in other languagescan be used to represent sparse (mostly emptydata structuresand much more here' rundown of their main properties python dictionaries areaccessed by keynot offset position dictionaries are sometimes called associative arrays or hashes (especially by users of other scripting languagesthey associate set of values with keysso you can fetch an item out of dictionary using the key under which you originally stored it you use the same indexing operation to get components in dictionary as you do in listbut the index takes the form of keynot relative offset lists and dictionaries