Converting File Input •  Aswiththeinputfunc.on,thereadline()methodcanonlyreturnstrings

•  Ifthefilecontainsnumericaldata,thestringsmustbeconvertedtothenumericalvalueusingtheint()orfloat()func.on:

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value=float(line)

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•  Thenewlinecharacterattheendofthelineisignoredwhenthestringisconvertedtoanumericalvalue

Writing To A File •  Forexample,wecanwritethestring"Hello,World!"toouroutputfileusingthestatement:

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outfile.write("Hello,World!\n")

outfile.write("Numberofentries:%d\nTotal:%8.2f\n"%(count,total))

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•  Unlikeprint()whenwri.ngtexttoanoutputfile,youmustexplicitlywritethenewlinecharactertostartanewline

•  YoucanalsowriteformaJedstringstoafilewiththewritemethod:

Example: File Reading/Writing •  Supposeyouaregivenatextfilethatcontainsasequenceoffloa.ng-pointvalues,storedonevalueperline

•  Youneedtoreadthevaluesandwritethemtoanewoutputfile,alignedinacolumnandfollowedbytheirtotalandaveragevalue

•  Iftheinputfilehasthecontents32.054.067.580.25115.0

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Example: File Reading/Writing (2) •  Theoutputfilewillcontain

32.0054.0067.5080.25115.00--------Total:348.75Average:69.75

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Example One •  Openthefiletotal.py

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Common Error •  BackslashesinFileNames

•  WhenusingaStringliteralforafilenamewithpathinforma.on,youneedtosupplyeachbackslashtwice:

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infile=open("c:\\homework\\input.txt","r")

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•  Asinglebackslashinsideaquotedstringistheescapecharacter,whichmeansthenextcharacterisinterpreteddifferently(forexample,‘\n’foranewlinecharacter)

•  Whenausersuppliesafilenameintoaprogram,theusershouldnottypethebackslashtwice

Text Input and Output SECTION 7.2

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Text Input and Output •  Inthefollowingsec.ons,youwilllearnhowtoprocesstextwithcomplexcontents,andyouwilllearnhowtocopewithchallengesthato^enoccurwithrealdata

•  ReadingWordsExample:

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forlineininputFile:line=line.rsplit()

Mary had a little lamb

Mary had a little lamb

input output

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Processing Text Input •  Thereare.meswhenyouwanttoreadinputby:

•  Eachword•  Eachline•  Asinglecharacter

•  Pythonprovidesmethodssuch:read(),split()andstrip()forthesetasks

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Processingtextinputisrequiredforalmostalltypesofprogramsthat

interactwiththeuser

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Text Input and Output •  Pythoncantreataninputfileasthoughitwereacontainerofstringsinwhicheachlinecomprisesanindividualstring

•  Forexample,thefollowingloopreadsalllinesfromafileandprintsthem:

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forlineininfile:print(line)

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•  Atthebeginningofeachitera.on,theloopvariablelineisassignedthevalueofastringthatcontainsthenextlineoftextinthefile

•  Thereisacri.caldifferencebetweenafileandacontainer:•  Onceyoureadthefileyoumustcloseitbeforeyoucaniterateoveritagain

An Example of Reading a File •  Wehaveafilethatcontainsacollec.onofwords;oneperline:

spam

and

eggs

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Removing The Newline (1) •  Recallthateachinputlineendswithanewline(\n)character•  Generally,thenewlinecharactermustberemovedbeforetheinputstringisused

•  Whenthefirstlineofthetextfileisread,thestringlinecontains

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Removing The Newline (2) •  Toremovethenewlinecharacter,applytherstrip()methodtothestring:

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line=line.rstrip()

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•  Thisresultsinthestring:

Character Strip Methods

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Character Strip Examples

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Reading Words •  Some.mesyoumayneedtoreadtheindividualwordsfromatextfile

•  Forexample,supposeourinputfilecontainstwolinesoftextMaryhadaliJlelamb,whosefleecewaswhiteassnow

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Reading Words (2) •  Wewouldliketoprinttotheterminal,onewordperline

MaryhadaliJle...

•  Becausethereisnomethodforreadingawordfromafile,youmustfirstreadalineandthensplititintoindividualwords

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line=line.rstrip()wordlist=line.split()

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Reading Words (3) •  Thesplitmethodreturnsthelistofsubstringsthatresultsfromspliengthestringateachblankspace

•  Forexample,iflinecontainsthestring:

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•  Itwillbesplitinto5substringsthatarestoredinalistinthesameorderinwhichtheyoccurinthestring:

Reading Words (4) •  No.cethatthelastwordinthelinecontainsacomma

•  Ifweonlywanttoprintthewordscontainedinthefilewithoutpunctua.onmarks,wecanstripthosefromthesubstringsusingtherstrip()methodintroducedintheprevioussec.on:

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word=word.rstrip(".,?!")

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Reading Words: Complete Example inputFile=open("lyrics.txt","r")

forlineininputFile:

line=line.rstrip()

wordList=line.split()

forwordinwordList:

word=word.rstrip(".,?!")

print(word)

inputFile.close()

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Example Two •  Openthefilelyrics.py

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Additional String Splitting Methods

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Additional String Splitting Examples

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