Think Python - Denison University

10 Chapter 2. Variables, expressions and statementsThey’re strings.Whenyoutypealargeinteger,youmightbetemptedtousecommasbetweengroupsofthreedigits,as in1,000,000. Thisis not alegal integer inPython, but itislegal:>>> print 1,000,0001 0 0Well, that’s not what we expected at all! Python interprets 1,000,000 as a comma-separated sequenceofintegers, which itprints withspaces between.Thisisthefirstexamplewehaveseenofasemanticerror: thecoderunswithoutproducinganerrormessage, but itdoesn’t do the“right” thing.2.2 VariablesOneofthemostpowerfulfeaturesofaprogramminglanguageistheabilitytomanipulatevariables.A variable isaname that referstoavalue.Anassignment statement creates new variables and gives them values:>>> message = 'And now for something completely different'>>> n = 17>>> pi = 3.1415926535897932Thisexamplemakesthreeassignments. Thefirstassignsastringtoanewvariablenamedmessage;thesecond gives the integer17ton;thethirdassigns the(approximate) value of π topi.A common way to represent variables on paper is to write the name with an arrow pointing to thevariable’s value. This kind of figure is called a state diagram because it shows what state each ofthe variables is in (think of it as the variable’s state of mind). This diagram shows the result of theprevious example:messagenpi’And now for something completely different’173.1415926535897931To display thevalue of avariable, you can useaprint statement:>>> print n17>>> print pi3.14159265359The type of avariable isthetype of thevalue itrefersto.>>> type(message)>>> type(n)>>> type(pi)