python习题Word格式.docx

python习题Word格式.docx

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hello"

anddescribeyourresult.Makenoteofwhenyouseethequotationmarksandwhenyoudon’t.

8.Typeprintcheesewithoutthequotationmarks.Theoutputwilllooksomethinglikethis:

9.Traceback（mostrecentcalllast）:

10.File"

line1,in?

NameError:

name'

cheese'

isnotdefined

Thisisarun-timeerror;

specifically,itisaNameError,andevenmorespecifically,itisanerrorbecausethenamecheeseisnotdefined.Ifyoudon’tknowwhatthatmeansyet,youwillsoon.

11.Type'

Thisisatest...'

atthePythonpromptandhitenter.Recordwhathappens.

Nowcreateapythonscriptnamedtest1.pywiththefollowingcontents（besuretosaveitbeforeyoutrytorunit）:

'

Whathappenswhenyourunthisscript?

Nowchangethecontentsto:

print'

andrunitagain.

Whathappenedthistime?

WheneveranexpressionistypedatthePythonprompt,itisevaluatedandtheresultisprintedonthelinebelow.'

isanexpression,whichevaluatesto'

（justliketheexpression42evaluatesto42）.Inascript,however,evaluationsofexpressionsarenotsenttotheprogramoutput,soitisnecessarytoexplicitlyprintthem.

2.13.Exercises¶

1.Recordwhathappenswhenyouprintanassignmentstatement:

2.>

>

printn=7

Howaboutthis?

print7+5

Orthis?

print5.2,"

this"

4-2,"

that"

5/2.0

Canyouthinkageneralruleforwhatcanfollowtheprintstatement?

Whatdoestheprintstatementreturn?

3.Takethesentence:

AllworkandnoplaymakesJackadullboy.Storeeachwordinaseparatevariable,thenprintoutthesentenceononelineusingprint.

4.Addparenthesistotheexpression6*1-2tochangeitsvaluefrom4to-6.

5.Placeacommentbeforealineofcodethatpreviouslyworked,andrecordwhathappenswhenyoureruntheprogram.

6.Thedifferencebetweeninputandraw_inputisthatinputevaluatestheinputstringandraw_inputdoesnot.Trythefollowingintheinterpreterandrecordwhathappens:

7.>

x=input（）

8.3.14

9.>

type（x）

10.>

x=raw_input（）

11.3.14

12.>

13.>

14.'

Theknightswhosay"

ni!

15.>

x

Whathappensifyoutrytheexampleabovewithoutthequotationmarks?

Describeandexplaineachresult.

16.StartthePythoninterpreterandenterbruce+4attheprompt.Thiswillgiveyouanerror:

bruce'

Assignavaluetobrucesothatbruce+4evaluatesto10.

17.Writeaprogram（Pythonscript）namedmadlib.py,whichaskstheusertoenteraseriesofnouns,verbs,adjectives,adverbs,pluralnouns,pasttenseverbs,etc.,andthengeneratesaparagraphwhichissyntacticallycorrectbutsemanticallyridiculous（seehttp:

//madlibs.orgforexamples）.

3.8.Exercises¶

1.Usingatexteditor,createaPythonscriptnamedtryme3.py.Writeafunctioninthisfilecallednine_linesthatusesthree_linestoprintnineblanklines.Nowaddafunctionnamedclear_screenthatprintsouttwenty-fiveblanklines.Thelastlineofyourprogramshouldbeacalltoclear_screen.

2.Movethelastlineoftryme3.pytothetopoftheprogram,sothefunctioncalltoclear_screenappearsbeforethefunctiondefinition.Runtheprogramandrecordwhaterrormessageyouget.Canyoustatearuleaboutfunctiondefinitionsandfunctioncallswhichdescribeswheretheycanappearrelativetoeachotherinaprogram?

3.Startingwithaworkingversionoftryme3.py,movethedefinitionofnew_lineafterthedefinitionofthree_lines.Recordwhathappenswhenyourunthisprogram.Nowmovethedefinitionofnew_linebelowacalltothree_lines（）.Explainhowthisisanexampleoftheruleyoustatedinthepreviousexercise.

4.Fillinthebodyofthefunctiondefinitionforcat_n_timessothatitwillprintthestring,s,ntimes:

5.defcat_n_times（s,n）:

<

fillinyourcodehere>

Savethisfunctioninascriptnamedimport_test.py.Nowataunixprompt,makesureyouareinthesamedirectorywheretheimport_test.pyislocated（lsshouldshowimport_test.py）.StartaPythonshellandtrythefollowing:

fromimport_testimport*

cat_n_times（'

Spam'

7）

SpamSpamSpamSpamSpamSpamSpam

Ifalliswell,yoursessionshouldworkthesameasthisone.Experimentwithothercallstocat_n_timesuntilyoufeelcomfortablewithhowitworks.

4.13.Exercises¶

1.Trytoevaluatethefollowingnumericalexpressionsinyourhead,thenusethePythoninterpretertocheckyourresults:

1.>

5%2

9%5

3.>

15%12

4.>

12%15

5.>

6%6

6.>

0%7

7%0

Whathappenedwiththelastexample?

Why?

Ifyouwereabletocorrectlyanticipatethecomputer’sresponseinallbutthelastone,itistimetomoveon.Ifnot,taketimenowtomakeupexamplesofyourown.Explorethemodulusoperatoruntilyouareconfidentyouunderstandhowitworks.

2.ifx<

y:

3.printx,"

islessthan"

y

4.elifx>

5.printx,"

isgreaterthan"

6.else:

7.printx,"

and"

y,"

areequal"

8.Wrapthiscodeinafunctioncalledcompare（x,y）.Callcomparethreetimes:

oneeachwherethefirstargumentislessthan,greaterthan,andequaltothesecondargument.

9.Tobetterunderstandbooleanexpressions,itishelpfultoconstructtruthtables.Twobooleanexpressionsarelogicallyequivalentifandonlyiftheyhavethesametruthtable.

ThefollowingPythonscriptprintsoutthetruthtableforanybooleanexpressionintwovariables:

pandq:

expression=raw_input（"

Enterabooleanexpressionintwovariables,pandq:

"

）

print"

pq%s"

%expression

length=len（"

%expression）

printlength*"

="

forpinTrue,False:

forqinTrue,False:

print"

%-7s%-7s%-7s"

%（p,q,eval（expression））

Youwilllearnhowthisscriptworksinlaterchapters.Fornow,youwilluseittolearnaboutbooleanexpressions.Copythisprogramtoafilenamedp_and_q.py,thenrunitfromthecommandlineandgiveit:

porq,whenpromptedforabooleanexpression.Youshouldgetthefollowingoutput:

pqporq

=====================

TrueTrueTrue

TrueFalseTrue

FalseTrueTrue

FalseFalseFalse

Nowthatweseehowitworks,let’swrapitinafunctiontomakeiteasiertouse:

deftruth_table（expression）:

length=len（"

printlength*"

forpinTrue,False:

WecanimportitintoaPythonshellandcalltruth_tablewithastringcontainingourbooleanexpressioninpandqasanargument:

fromp_and_qimport*

truth_table（"

porq"

pqporq

Usethetruth_tablefunctionswiththefollowingbooleanexpressions,recordingthetruthtableproducedeachtime:

1.not（porq）

2.pandq

3.not（pandq）

4.not（p）ornot（q）

5.not（p）andnot（q）

Whichofthesearelogicallyequivalent?

10.EnterthefollowingexpressionsintothePythonshell:

11.TrueorFalse

12.TrueandFalse

13.not（False）andTrue

14.Trueor7

15.Falseor7

16.Trueand0

17.Falseor8

18."

happy"

and"

sad"

19."

or"

20."

21."

Analyzetheseresults.Whatobservationscanyoumakeaboutvaluesofdifferenttypesandlogicaloperators?

Canyouwritetheseobservationsintheformofsimplerulesaboutandandorexpressions?

22.ifchoice=='

a'

:

23.function_a（）

24.elifchoice=='

b'

25.function_b（）

26.elifchoice=='

c'

27.function_c（）

28.else:

29.print"

Invalidchoice."

30.Wrapthiscodeinafunctioncalleddispatch（choice）.Thendefinefunction_a,function_b,andfunction_csothattheyprintoutamessagesayingtheywerecalled.Forexample:

31.deffunction_a（）:

32.print"

function_awascalled..."

Putthefourfunctions（dispatch,function_a,function_b,andfunction_cintoascriptnamedch04e05.py.Atthebottomofthisscriptaddacalltodispatch（'

）.Youroutputshouldbe:

function_bwascalled...

Finally,modifythescriptsothatusercanenter‘a’,‘b’,or‘