SolutionsChapter 10.docx

SolutionsChapter 10.docx

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SolutionsChapter10

Solutions-Chapter10

10-1:

LearningPython

Openablankfileinyourtexteditorandwriteafewlinessummarizingwhatyou’velearnedaboutPythonsofar.Starteachlinewiththephrase InPythonyoucan… Savethefileaslearning_python.txt inthesamedirectoryasyourexercisesfromthischapter.Writeaprogramthatreadsthefileandprintswhatyouwrotethreetimes.Printthecontentsoncebyreadingintheentirefile,oncebyloopingoverthefileobject,andoncebystoringthelinesinalistandthenworkingwiththemoutsidethe with block.

learning_python.txt:

InPythonyoucanstoreasmuchinformationasyouwant.

InPythonyoucanconnectpiecesofinformation.

InPythonyoucanmodelreal-worldsituations.

learning_python.py:

filename='learning_python.txt'

print（"---Readingintheentirefile:

"）

withopen（filename）asf:

contents=f.read（）

print（contents）

print（"\n---Loopingoverthelines:

"）

withopen（filename）asf:

forlineinf:

print（line.rstrip（））

print（"\n---Storingthelinesinalist:

"）

withopen（filename）asf:

lines=f.readlines（）

forlineinlines:

print（line.rstrip（））

Output:

---Readingintheentirefile:

InPythonyoucanstoreasmuchinformationasyouwant.

InPythonyoucanconnectpiecesofinformation.

InPythonyoucanmodelreal-worldsituations.

---Loopingoverthelines:

InPythonyoucanstoreasmuchinformationasyouwant.

InPythonyoucanconnectpiecesofinformation.

InPythonyoucanmodelreal-worldsituations.

---Storingthelinesinalist:

InPythonyoucanstoreasmuchinformationasyouwant.

InPythonyoucanconnectpiecesofinformation.

InPythonyoucanmodelreal-worldsituations.

10-2:

LearningC

Youcanusethe replace（） methodtoreplaceanywordinastringwithadifferentword.Here’saquickexampleshowinghowtoreplace 'dog' with 'cat' inasentence:

>>>message="Ireallylikedogs."

>>>message.replace（'dog','cat'）

'Ireallylikecats.'

Readineachlinefromthefileyoujustcreated, learning_python.txt,andreplacetheword Pythonwiththenameofanotherlanguage,suchas C.Printeachmodifiedlinetothescreen.

filename='learning_python.txt'

withopen（filename）asf:

lines=f.readlines（）

forlineinlines:

#Getridofnewline,thenreplacePythonwithC.

line=line.rstrip（）

print（line.replace（'Python','C'））

Output:

InCyoucanstoreasmuchinformationasyouwant.

InCyoucanconnectpiecesofinformation.

InCyoucanmodelreal-worldsituations.

Youcanuse rstrip（） and replace（） onthesameline.Thisiscalled chaining methods.Inthefollowingcodethenewlineisstrippedfromtheendofthelineandthen Python isreplacedby C.Theoutputisidenticaltothecodeshownabove.

filename='learning_python.txt'

withopen（filename）asf:

lines=f.readlines（）

forlineinlines:

#Getridofnewline,thenreplacePythonwithC.

print（line.rstrip（）.replace（'Python','C'））

10-3:

Guest

Writeaprogramthatpromptstheuserfortheirname.Whentheyrespond,writetheirnametoafilecalled guest.txt.

name=input（"What'syourname?

"）

filename='guest.txt'

withopen（filename,'w'）asf:

f.write（name）

Output:

What'syourname?

eric

guest.txt:

eric

10-4:

GuestBook

Writea while loopthatpromptsusersfortheirname.Whentheyentertheirname,printagreetingtothescreenandaddalinerecordingtheirvisitinafilecalled guest_book.txt.Makesureeachentryappearsonanewlineinthefile.

filename='guest_book.txt'

print（"Enter'quit'whenyouarefinished."）

whileTrue:

name=input（"\nWhat'syourname?

"）

ifname=='quit':

break

else:

withopen（filename,'a'）asf:

f.write（name+"\n"）

print（"Hi"+name+",you'vebeenaddedtotheguestbook."）

Output:

Enter'quit'whenyouarefinished.

What'syourname?

eric

Hieric,you'vebeenaddedtotheguestbook.

What'syourname?

willie

Hiwillie,you'vebeenaddedtotheguestbook.

What'syourname?

ever

Hiever,you'vebeenaddedtotheguestbook.

What'syourname?

erin

Hierin,you'vebeenaddedtotheguestbook.

What'syourname?

quit

guest_book.txt:

eric

willie

ever

erin

10-5:

ProgrammingPoll

Writea while loopthataskspeoplewhytheylikeprogramming.Eachtimesomeoneentersareason,addtheirreasontoafilethatstoresalltheresponses.

filename='programming_poll.txt'

responses=[]

whileTrue:

response=input（"\nWhydoyoulikeprogramming?

"）

responses.append（response）

continue_poll=input（"Wouldyouliketoletsomeoneelserespond?

（y/n）"）

ifcontinue_poll!

='y':

break

withopen（filename,'a'）asf:

forresponseinresponses:

f.write（response+"\n"）

Output:

Whydoyoulikeprogramming?

Programmerscanbuildalmostanythingtheycanimagine.

Wouldyouliketoletsomeoneelserespond?

（y/n）y

Whydoyoulikeprogramming?

It'sreallyfun,andreallysatisfying.

Wouldyouliketoletsomeoneelserespond?

（y/n）y

Whydoyoulikeprogramming?

Itjustnevergetsold.

Wouldyouliketoletsomeoneelserespond?

（y/n）n

programming_poll.txt:

Programmerscanbuildalmostanythingtheycanimagine.

It'sreallyfun,andreallysatisfying.

Itjustnevergetsold.

10-6:

Addition

Onecommonproblemwhenpromptingfornumericalinputoccurswhenpeopleprovidetextinsteadofnumbers.Whenyoutrytoconverttheinputtoan int,you’llgeta ValueError.Writeaprogramthatpromptsfortwonumbers.Addthemtogetherandprinttheresult.CatchtheTypeError ifeitherinputvalueisnotanumber,andprintafriendlyerrormessage.Testyourprogrambyenteringtwonumbersandthenbyenteringsometextinsteadofanumber.

try:

x=input（"Givemeanumber:

"）

x=int（x）

y=input（"Givemeanothernumber:

"）

y=int（y）

exceptValueError:

print（"Sorry,Ireallyneededanumber."）

else:

sum=x+y

print（"Thesumof"+str（x）+"and"+str（y）+"is"+str（sum）+"."）

Outputwithtwointegers:

Givemeanumber:

23

Givemeanothernumber:

47

Thesumof23and47is70.

Outputwithnon-numericalinput:

Givemeanumber:

23

Givemeanothernumber:

fred

Sorry,Ireallyneededanumber.

10-7:

AdditionCalculator

WrapyourcodefromExercise10-6ina while loopsotheusercancontinueenteringnumberseveniftheymakeamistakeandentertextinsteadofanumber.

print（"Enter'q'atanytimetoquit.\n"）

whileTrue:

try:

x=input（"\nGivemeanumber:

"）

ifx=='q':

break

x=int（x）

y=input（"Givemeanothernumber:

"）

ify=='q':

break

y=int（y）

exceptValueError:

print（"Sorry,Ireallyneededanumber."）

else:

sum=x+y

print（"Thesumof"+str（x）+"and"+str（y）+"is"+str（sum）+"."）

Output:

Enter'q'atanytimetoquit.

Givemeanumber:

23

Givemeanothernumber:

47

Thesumof23and47is70.

Givemeanumber:

three

Sorry,Ireallyneededanumber.

Givemeanumber:

3

Givemeanothernumber:

five

Sorry,Ireallyneededanumber.

Givemeanumber:

-12

Givemeanothernumber:

20

Thesumof-12and20is8.

Givemeanumber:

q

10-8:

CatsandDogs

Maketwofiles, cats.txt and dogs.txt.Storeatleastthreenamesofcatsinthefirstfileandthreenamesofdogsinthesecondfile.Writeaprogramthattriestoreadthesefilesandprintthecontentsofthefiletothescreen.Wrapyourcodeina try-except blocktocatchthe FileNotFounderror,andprintafriendlymessageifafileismissing.Moveoneofthefilestoadifferentlocationonyoursystem,andmakesurethecodeinthe except blockexecutesproperly.

cats.txt:

henry

clarence

mildred

dogs.txt:

willie

annahootz

summit

cats_and_dogs.py:

filenames=['cats.txt','dogs.txt']

forfilenameinfilenames:

print（"\nReadingfile:

"+filename）

try:

withopen（filename）asf:

contents=f.read（）

print（contents）

exceptFileNotFoundError:

print（"Sorry,Ican'tfindthatfile."）

Outputwithbothfiles:

Readingfile:

cats.txt

henry

clarence

mildred

Readingfile:

dogs.txt

willie

annahootz

summit

Outputaftermoving cats.txt:

Readingfile:

cats.txt

Sorry,Ican'tfindthatfile.

Readingfile:

dogs.txt

willie

annahootz

summit

10-9:

SilentCatsandDogs

Modifyyour except blockinExercise10-8tofailsilentlyifeitherfileismissing.

filenames=['cats.txt','dogs.txt']

forfilenameinfilenames:

try:

withopen（filename）asf:

contents=f.read（）

exceptFileNotFoundError:

pass

else:

print（"\nReadingfile:

"+filename）

print（contents）

Outputwhenbothfilesexist:

Readingfile:

cats.txt

henry

clarence

mildred

Readingfile:

dogs.txt

willie

annahootz

summit

Outputwhen cats.txt hasbeenmoved:

Readingfile:

dogs.txt

willie

annahootz

summit

10-11:

FavoriteNumber

Writeaprogramthatpromptsfortheuser’sfavoritenumber.Use json.dump（） tostorethisnumberinafile.Writeaseparateprogramthatreadsinthisvalueandprintsthemessage,“Iknowyourfavoritenumber!

It’s_____.”

favorite_number_write.py:

importjson

number=input（"What'syourfavoritenumber?

"）

withopen（'favorite_number.json','w'）asf:

json.dump（number,f）

print（"Thanks!

I'llrememberthat."）

Output:

What'syourfavoritenumber?

42

Thanks!

I'llrememberthat.

favorite_number_read.py:

importjson

withopen（'favorite_number.json'）asf:

number=json.load（f）

print（"Iknowyourfavoritenumber!

It's"+str（number）+"."）

Output:

Iknowyourfavoritenumber!

It's42.

10-12:

FavoriteNumberRemembered

CombinethetwoprogramsfromExercise10-11intoonefile.Ifthenumberisalreadystored,reportthefavoritenumbertotheuser.Ifnot,promptfortheuser’sfavoritenumberandstoreitinafile.Runtheprogramtwicetoseethatitworks.

importjson

try:

withopen（'favorite_number.json'）asf:

number=json.load（f）

exceptFileNotFoundError:

n