sequence typesthe listtupleand str classes the listtupleand str classes are sequence types in pythonrepresenting collection of values in which the order is significant the list class is the most generalrepresenting sequence of arbitrary objects (akin to an "arrayin other languagesthe tuple class is an immutable version of the list classbenefiting from streamlined internal representation the str class is specially designed for representing an immutable sequence of text characters we note that python does not have separate class for charactersthey are just strings with length one the list class list instance stores sequence of objects list is referential structureas it technically stores sequence of references to its elements (see figure elements of list may be arbitrary objects (including the none objectlists are array-based sequences and are zero-indexedthus list of length has elements indexed from to inclusive lists are perhaps the most used container type in python and they will be extremely central to our study of data structures and algorithms they have many valuable behaviorsincluding the ability to dynamically expand and contract their capacities as needed in this we will discuss only the most basic properties of lists we revisit the inner working of all of python' sequence types as the focus of python uses the characters as delimiters for list literalwith itself being an empty list as another examplered green blue is list containing three string instances the contents of list literal need not be expressed as literalsif identifiers and have been establishedthen syntax [abis legitimate the listconstructor produces an empty list by default howeverthe constructor will accept any parameter that is of an iterable type we will discuss iteration further in section but examples of iterable types include all of the standard container types ( stringslisttuplessetsdictionariesfor examplethe syntax listhello produces list of individual charactersh because an existing list is itself iterablethe syntax backup list(datacan be used to construct new list instance referencing the same contents as the original primes figure python' internal representation of list of integersinstantiated as prime [ the implicit indices of the elements are shown below each entry