2.5.ASSIGNMENTSTATEMENTS 17
print
print
print
print
Ina nutshell,thesetemplatesshow thataprintstatementconsistsofthekeywordprintfollowedbyzero
ormoreexpressions,whichareseparatedbycommas.Theanglebracket notation( ) is usedtoindicate
“slots”thatarefilledinbyotherfragmentsofPythoncode.Thenameinsidethebracketsindicatewhatis
missing;exprstandsforanexpression. Theellipses(“...”) indicateanindefiniteseries(ofexpressions,
inthiscase).Youdon’t actuallytypethedots.Thefourthversionshowsthataprintstatementmaybe
optionallyendedwitha comma.Thatis allthereis toknow aboutthesyntaxofprint.
Asfarassemantics,aprintstatementdisplaysinformationintextualform.Any suppliedexpressions
areevaluatedlefttoright,andtheresultingvaluesaredisplayedona singlelineofoutputina left-to-right
fashion.A singleblankspacecharacteris placedbetweenthedisplayedvalues.
Normally, successiveprintstatementswilldisplayonseparatelinesofthescreen.A bareprint(first
versionabove)canbeusedtogeta blanklineofoutput.If aprintstatementendswitha comma(fourth
version),a finalspaceis appendedtotheline,buttheoutputdoesnotadvancetothenextline.Usingthis
method,multipleprintstatementscanbeusedtogeneratea singlelineofoutput.
Puttingit alltogether, thissequenceofprintstatements
print 3+4
print 3, 4, 3 + 4
print
print 3, 4,
print 3+4
print "The answer is",3 + 4
producesthisoutput
7
3 4 7
3 4 7
The answer is 7
Thatlastprintstatementmaybea bitconfusing.Accordingtothesyntaxtemplatesabove,print
requiresa sequenceofexpressions.Thatmeans"The answer is"mustbeanexpression.Infact,itis
anexpression,butit doesn’t producea number. Instead,it producesanotherkindofdatacalledastring.
Asequenceofcharactersenclosedinquotesis a stringliteral.Stringswillbediscussedindetailina later
chapter. Fornow, considerthisa convenientwayoflabelingoutput.
2.5 AssignmentStatements.
2.5.1 SimpleAssignment.
OneofthemostimportantkindsofstatementsinPythonis theassignmentstatement.We’ve alreadyseena
numberoftheseinourpreviousexamples.Thebasicassignmentstatementhasthisform:
Herevariableis anidentifierandexprisanexpression.Thesemanticsoftheassignmentisthatthe
expressionontherightsideis evaluatedtoproducea value,whichis thenassociatedwiththevariablenamed
ontheleftside.
Herearesomeoftheassignmentswe’ve alreadyseen.
x = 3.9 x (1 - x)
fahrenheit = 9.0 / 5.0* celsius + 32
x = 5