you can' do with list on the other handlists let you append new itemswhich is something string doesn' support collections are simply another kind of sequencealbeit more complex sequence than you find in either string or list no matter which sequence you usethey all support two functionsindex(and count(the index(function always returns the position of specified item in the sequence for exampleyou can return the position of character in string or the position of an object in list the count(function returns the number of times specific item appears in the list againthe kind of specific item depends upon the kind of sequence you can use collections to create database-like structures using python each collection type has different purposeand you use the various types in specific ways the important idea to remember is that collections are simply another kind of sequence as with every other kind of sequencecollections always support the index(and count(functions as part of their base functionality python is designed to be extensible howeverit does rely on base set of collections that you can use to create most application types this describes the most common collectionstuplea tuple is collection used to create complex list-like sequences an advantage of tuples is that you can nest the content of tuple this feature lets you create structures that can hold employee records or - coordinate pairs dictionaryas with the real dictionariesyou create key/value pairs when using the dictionary collection (think of word and its associated definitiona dictionary provides incredibly fast search times and makes ordering data significantly easier stackmost programming languages support stacks directly howeverpython doesn' support the stackalthough there' work-around for that stack is first in/first out (fifosequence think of pile of pancakesyou can add new pancakes to the top and also take them off of the top stack is an important collection that you can simulate in python using listwhich is precisely what this does queuea queue is last in/first out (lifocollection you use it to track items that need to be processed in some way think of queue as line at the bank you go into the linewait your turnand are eventually called to talk with teller dequea double-ended queue (dequeis queue-like structure that lets you add or remove items from either endbut not from the middle you can use deque as queue or stack or any other kind of collection to which you're adding and from which you're removing items in an orderly manner (in contrast to liststuplesand dictionarieswhich allow randomized access and management