Chapter 6

Concatenation •  Theconcatena*onoftwolistsisanewlistthatcontainstheelementsofthefirstlist,followedbytheelementsofthesecond

myFriends=["Fritz","Cindy"]yourFriends=["Lee","Pat","Phuong"]

ourFriends=myFriends+yourFriends#SetsourFriendsto["Fritz","Cindy","Lee","Pat","Phuong"]

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•  Twolistscanbeconcatenatedbyusingtheplus(+)operator:

Replication •  Aswithstringreplica*onoftwolistsisanewlistthatcontainstheelementsofthefirstlist,followedbytheelementsofthesecond

monthInQuarter=[1,2,3]*4

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monthlyScores=[0]*12

•  Resultsinthelist[1,2,3,1,2,3,1,2,3,1,2,3]•  Youcanplacetheintegeroneithersideofthe“*”operator

•  Theintegerspecifieshowmanycopiesofthelistshouldbeconcatenated

•  Onecommonuseofreplica*onistoini*alizealistwithafixedvalue

Equality / Inequality Testing •  Youcanusethe==operatortocomparewhethertwolistshavethesameelements,inthesameorder.

[1,4,9]==[1,4,9]#True[1,4,9]==[4,1,9]#False.

[1,4,9]!=[4,9]#True.

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•  Theoppositeof==is!=.

Sum, Maximum, Minimum •  Ifyouhavealistofnumbers,thesum()func*onyieldsthesumofallvaluesinthelist.

sum([1,4,9,16])#Yields30

max([1,16,9,4])#Yields16min(["Fred","Ann","Sue”])#Yields"Ann"

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•  Foralistofnumbersorstrings,themax()andmin()func*onsreturnthelargestandsmallestvalue:

Sorting •  Thesort()methodsortsalistofnumbersorstrings.

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values=[1,16,9,4]values.sort()#Nowvaluesis[1,4,9,16]

Copying Lists •  Asdiscussed,listvariablesdonotthemselvesholdlistelements

•  Theyholdareferencetotheactuallist

•  Ifyoucopythereference,yougetanotherreferencetothesamelist:

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prices=values

Copying Lists (2) •  Some*mes,youwanttomakeacopyofalist;thatis,anewlistthathasthesameelementsinthesameorderasagivenlist

•  Usethelist()func*on:

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prices=list(values)

Slices of a List •  Some*mesyouwanttolookatapartofalist.Supposeyouaregivenalistoftemperatures,onepermonth:

temperatures=[18,21,24,33,39,40,39,36,30,22,18]

•  Youareonlyinterestedinthetemperaturesforthethirdquarter,withindexvalues6,7,and8

•  Youcanusethesliceoperatortoobtainthem:

thirdQuarter=temperatures[6:9]

•  Theargumentsarethefirstelementtoinclude,andthefirsttoexclude•  Soinourexamplewegetelements6,7,and8

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Slices (2) •  Bothindexesusedwiththesliceoperatorareop*onal•  IfthefirstindexisomiYed,allelementsfromthefirstareincluded

•  Theslicetemperatures[:6]

•  Includesallelementsupto,butnotincluding,posi*on6

•  Theslicetemperatures[6:]

•  Includesallelementsstar*ngatposi*on6totheendofthelist

•  Youcanassignvaluestoaslice:temperatures[6:9]=[45,44,40]

•  Replacesthevaluesinelements6,7,and8

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Common List Functions And Operators

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Common List Functions And Operators (2)

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Common List Methods

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Common List Algorithms SECTION 6.3

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Common List Algorithms •  FillingaList•  CombiningListElements

•  ElementSeparators

•  MaximumandMinimum

•  LinearSearch

•  Collec*ngandCoun*ngMatches

•  RemovingMatches

•  SwappingElements

•  ReadingInput

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Filling a List •  Thisloopcreatesandfillsalistwithsquares(0,1,4,9,16,...)

values=[]foriinrange(n):values.append(i*i)

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Combining List Elements •  Hereishowtocomputeasumofnumbers:

result=0.0forelementinvalues:result=result+element

result=""forelementinnames:result=result+element

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•  Toconcatenatestrings,youonlyneedtochangetheini*alvalue:

Element Separators •  Whenyoudisplaytheelementsofalist,youusuallywanttoseparatethem,ocenwithcommasorver*callines,likethis:

Harry,Emily,Bob

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Element Separators (2) •  Addtheseparatorbeforeeachelement(there’sonefewerseparatorthantherearenumbers)inthesequenceexcepttheini*alone(withindex0),likethis:

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foriinrange(len(names)):ifi>0:result=result+","result=result+names[i]

Element Separators (3) •  Ifyouwanttoprintvalueswithoutaddingthemtoastring:

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foriinrange(len(values)):ifi>0:print("|",end="")print(values[i],end="")print()

Maximum and Minimum •  Hereistheimplementa*onofthemaxalgorithm(alreadycoveredinChapter4,thisoneisjustspecifictoalist):

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largest=values[0]foriinrange(1,len(values)):ifvalues[i]>largest:largest=values[i]

smallest=values[0]foriinrange(1,len(values)):ifvalues[i]<smallest:smallest=values[i]

Linear Search •  Findingthefirstvaluethatis>100.Youneedtovisitallelementsun*lyouhavefoundamatchoryouhavecometotheendofthelist:

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limit=100pos=0found=Falsewhilepos<len(values)andnotfound:ifvalues[pos]>limit:found=Trueelse:pos=pos+1iffound:print("Foundatposition:",pos)else:print("Notfound")

A linear search inspects elements in sequence until a match is found.

Collecting and Counting Matches •  Collec*ngallmatches

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limit=100result=[]forelementinvalues:if(element>limit):result.append(element)

limit=100counter=0forelementinvalues:if(element>limit):counter=counter+1

•  Coun*ngmatches

Removing Matches •  Removeallelementsthatmatchapar*cularcondi*on

•  Example:removeallstringsoflength<4fromalist

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i=0whilei<len(words):word=words[i]iflen(word)<4:words.pop(i)else:i=i+1

Swapping Elements •  Forexample,youcansortalistbyrepeatedlyswappingelementsthatarenotinorder

•  Swaptheelementsatposi*onsiandjofalistvalues

•  We’dliketosetvalues[i]tovalues[j].Butthatoverwritesthevaluethatiscurrentlystoredinvalues[i],sowewanttosavethatfirst:

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Before moving a new value into a location (say blue) copy blue’s value elsewhere and then move black’s value into blue. Then move the temporary value (originally in blue) into black.