the tuple class the tuple class provides an immutable version of sequenceand therefore its instances have an internal representation that may be more streamlined than that of list while python uses the characters to delimit listparentheses delimit tuplewith being an empty tuple there is one important subtlety to express tuple of length one as literala comma must be placed after the elementbut within the parentheses for example( ,is one-element tuple the reason for this requirement is thatwithout the trailing commathe expression ( is viewed as simple parenthesized numeric expression the str class python' str class is specifically designed to efficiently represent an immutable sequence of charactersbased upon the unicode international character set strings have more compact internal representation than the referential lists and tuplesas portrayed in figure figure python stringwhich is an indexed sequence of characters string literals can be enclosed in single quotesas in hello or double quotesas in "hellothis choice is convenientespecially when using another of the quotation characters as an actual character in the sequenceas in "don worryalternativelythe quote delimiter can be designated using backslash as so-called escape characteras in dont worry because the backslash has this purposethe backslash must itself be escaped to occur as natural character of the string literalas in :\\python\for string that would be displayed as :\pythonother commonly escaped characters are \ for newline and \ for tab unicode characters can be includedsuch as \ ac for the string or ""to begin and end string python also supports using the delimiter literal the advantage of such triple-quoted strings is that newline characters can be embedded naturally (rather than escaped as \nthis can greatly improve the readability of longmultiline strings in source code for exampleat the beginning of code fragment rather than use separate print statements for each line of introductory outputwe can use single print statementas followsprint("""welcome to the gpa calculator please enter all your letter gradesone per line enter blank line to designate the end """