(continued from previous pagea [del can also be used to delete entire variablesdel referencing the name hereafter is an error (at least until another value is assigned to itwe'll find other uses for del later tuples and sequences we saw that lists and strings have many common propertiessuch as indexing and slicing operations they are two examples of sequence data types (see typesseqsince python is an evolving languageother sequence data types may be added there is also another standard sequence data typethe tuple tuple consists of number of values separated by commasfor instancet 'hello! [ ( 'hello!'tuples may be nestedu ( (( 'hello!')( )tuples are immutablet[ traceback (most recent call last)file ""line in typeerror'tupleobject does not support item assignment but they can contain mutable objectsv ([ ][ ] ([ ][ ]as you seeon output tuples are always enclosed in parenthesesso that nested tuples are interpreted correctlythey may be input with or without surrounding parenthesesalthough often parentheses are necessary anyway (if the tuple is part of larger expressionit is not possible to assign to the individual items of tuplehowever it is possible to create tuples which contain mutable objectssuch as lists though tuples may seem similar to liststhey are often used in different situations and for different purposes tuples are immutableand usually contain heterogeneous sequence of elements that are accessed via unpacking (see later in this sectionor indexing (or even by attribute in the case of namedtupleslists are mutableand their elements are usually homogeneous and are accessed by iterating over the list special problem is the construction of tuples containing or itemsthe syntax has some extra quirks to accommodate these empty tuples are constructed by an empty pair of parenthesesa tuple with one item is constructed by following value with comma (it is not sufficient to enclose single value in parenthesesuglybut effective for exampleempty (singleton 'hello'len(empty<-note trailing comma (continues on next page data structures