Python: The Ultimate Beginner's Guide! -...

PythonTheUltimateBeginner’sGuide!

AndrewJohansen

Copyright2016byAndrewJohansen-Allrightsreserved.

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TableofContentsIntroduction

Chapter1GettingAcquaintedwithPython

Chapter2InstallingPython

Chapter3InteractingwithPython

Chapter4PythonSyntax

Chapter5VariablesandDataTypes

Chapter6BasicOperators

Chapter7Built-inFunctions

Chapter8ConditionalStatements

Chapter9Loops

Chapter10User-DefinedFunctions

Chapter11IntroductiontoClassesandObject-OrientedProgramming

Conclusion

Introduction

Iwanttothankyouandcongratulateyouforpurchasingthisbook…

“Python:TheUltimateBeginner’sGuide!”

ThisbookcontainsprovenstepsandstrategiesonlearningPythonProgrammingquicklyandeasily.

Pythonisapowerfulandflexibleprogramminglanguage.Itusesconciseandeasy-to-learnsyntax which enables programmers to write more codes and develop more complexprogramsinamuchshortertime.

Python:TheUltimateBeginner’sGuideprovidesallessentialprogrammingconceptsandinformationyouneedtostartdevelopingyourownPythonprogram.Thebookprovidesacomprehensivewalk-throughofPythonprogramming inaclear, straightforwardmannerthatbeginnerswill appreciate. Important concepts are introduced througha step-by-stepdiscussionandreinforcedbyrelevantexamplesandillustrations.Youcanusethisbookasaguidetohelpyouexplore,harness,andgainappreciationofthecapabilitiesandfeaturesofPython.

Thanksagainforpurchasingthisbook,Ihopeyouenjoyit!

Chapter1GettingAcquaintedwithPython

Python is an open source, high-level programming language developed by Guido vanRossuminthelate1980sandpresentlyadministeredbyPythonSoftwareFoundation.ItcamefromtheABClanguagethathehelpedcreateearlyoninhiscareer.

Pythonisapowerfullanguagethatyoucanusetocreategames,writeGUIs,anddevelopwebapplications.

Itisahigh-levellanguage.ReadingandwritingcodesinPythonismuchlikereadingandwriting regular English statements. Because they are not written in machine-readablelanguage,Pythonprogramsneedtobeprocessedbeforemachinescanrunthem.

Python is an interpreted language. This means that every time a program is run, itsinterpreterrunsthroughthecodeandtranslatesitintomachine-readablebytecode.

Python is an object-oriented language that allows users to manage and control datastructures or objects to create and run programs. Everything in Python is, in fact, firstclass. All objects, data types, functions, methods, and classes take equal position inPython.

Programminglanguagesarecreatedtosatisfytheneedsofprogrammersandusersforaneffective tool todevelopapplications that impact lives, lifestyles, economy,and society.They helpmake lives better by increasing productivity, enhancing communication, andimproving efficiency. Languages die and become obsolete when they fail to live up toexpectations and are replaced and superseded by languages that are more powerful.Python is a programming language that has stood the test of time and has remainedrelevantacrossindustriesandbusinessesandamongprogrammers,andindividualusers.Itis a living, thriving, and highly useful language that is highly recommended as a firstprogramminglanguageforthosewhowanttodiveintoandexperienceprogramming.

AdvantagesofUsingPython

Here are reasonswhy youwould prefer to learn and use Python over other high levellanguages:

Readability

Pythonprogramsuseclear,simple,andconciseinstructionsthatareeasytoreadevenbythosewhohavenosubstantialprogrammingbackground.ProgramswritteninPythonare,therefore,easiertomaintain,debug,orenhance.

Higherproductivity

CodesusedinPythonareconsiderablyshorter,simpler,andlessverbosethanotherhigh-level programming languages such as Java and C++. In addition, it has well-designedbuilt-infeaturesandstandardlibraryaswellasaccesstothirdpartymodulesandsourcelibraries.ThesefeaturesmakeprogramminginPythonmoreefficient.

Lesslearningtime

Python is relatively easy to learn.Many findPython a good first language for learningprogrammingbecauseitusessimplesyntaxandshortercodes.

Runsacrossdifferentplatforms

PythonworksonWindows,Linux/UNIX,MacOSX,otheroperatingsystemsandsmall-formdevices. It also runsonmicrocontrollersused inappliances, toys, remotecontrols,embeddeddevices,andothersimilardevices.

Chapter2InstallingPython

InstallingPythoninWindows

To install Python, you must first download the installation package of your preferredversionfromthislink:

https://www.python.org/downloads/

Onthispage,youwillbeaskedtochoosebetweenthetwolatestversionsforPython2and3:Python3.5.1andPython2.7.11.Alternatively,ifyouarelookingforaspecificrelease,youcanscrolldownthepagetofinddownloadlinksforearlierversions.

Youwouldnormallyopttodownloadthelatestversion,whichisPython3.5.1.ThiswasreleasedonDecember7,2015.However,youmayoptforthelatestversionofPython2,2.7.11.Your preferenceswill usually depend onwhich versionwill bemost usable foryourproject.WhilePython3isthepresentandfutureofthelanguage,issuessuchasthirdpartyutilityorcompatibilitymayrequireyoutodownloadPython2.

InstallingPythoninMac

https://www.python.org/downloads/

Ifyou’reusingaMac,youcandownloadtheinstallationpackagefromthislink:

https://www.python.org/downloads/mac-osx/

RunningtheInstallationfile:

Onceyou’refinishedwiththedownload,youcanproceedtoinstallationbyclickingonthedownloaded.exefile.StandardinstallationwillincludeIDLE,pip,anddocumentation.

https://www.python.org/downloads/mac-osx/

Chapter3InteractingwithPython

Pythonisaflexibleanddynamiclanguagethatyoucanuseindifferentways.Youcanuseitinteractivelywhenyousimplywanttotestacodeorastatementonaline-by-linebasisorwhenyou’re exploring its features.You canuse it in scriptmodewhenyouwant tointerpretanentirefileofstatementsorapplicationprogram.

TousePythoninteractively,youcanuseeithertheCommandLinewindowortheIDLEDevelopmentEnvironment.

CommandLineInteraction

ThecommandlineisthemoststraightforwardwaytoworkwithPython.YoucaneasilyvisualizehowPythonworksas it responds toeverycompletedcommandenteredon the>>> prompt. It may not be the most preferred interaction with Python, but it is thesimplestwaytoexplorehowPythonworks.

StartingPython

There are differentways to access Python’s command line depending on the operatingsysteminstalledonyourmachine:

Ifyou’reusingWindows,youcanstartthePythoncommandlinebyclickingonitsiconormenuitemontheStartmenu.

YoumayalsogotothefoldercontainingtheshortcutortheinstalledfilesandclickonthePythoncommandline.

Ifyou’reusingGNU/Linux,UNIX,andMacOSsystems,youhavetoruntheTerminalToolandenterthePythoncommandtostartyoursession.

We use commands to tell the computer what to do. When you want Python to dosomethingforyou,youhavetoinstructitbyenteringcommandsthatit isfamiliarwith.Pythonwill then translate these commands to instructions that your computerordevicecanunderstandandexecute.

ToseehowPythonworks,youcanusetheprintcommandtoprinttheuniversalprogram“Hello,World!”

1.OpenPython’scommandline.

2.Atthe>>>prompt,typethefollowing:

print(“Hello,World!”)

3.PressentertotellPythonthatyou’redonewithyourcommand.Veryquickly,thecommandlinewindowwilldisplayHello,World!onthefollowingline:

Pythonrespondedcorrectlybecauseyougaveitacommandinaformatthatitrequires.Toseehowitrespondswhenyouaskittoprintthesamestringusingawrongsyntaxfortheprintcommand,typeandenterthefollowingcommandonthePythoncommandprompt:

Print(“Hello,World!”)

ThisishowPythonwillrespond:

Syntaxerror:invalidsyntax

You’llgetsyntaxerrormessageswheneveryouenterinvalidorincompletestatements.Inthis case, you typed print with a capital letter which is a big no to a case-sensitivelanguagelikePython.

Ifyou’rejustusingPythoninteractively,youcandoawaywiththeprintcommandentirelybyjusttypingyourstatementwithinquotessuchas“Hello,World!”

ExitingPython

ToexitfromPython,youcantypeanyofthesecommands:

quit()

exit()

Control-Zthenpressenter

IDLE:Python’sIntegratedDevelopmentEnvironment(IDE)

The IDLE (Integrated Development and Learning Environment) tool is included inPython’s installation package but you can choose to downloadmore sophisticated thirdpartyIDEs.

TheIDLEtooloffersamoreefficientplatformtowriteyourcodeandworkinteractively

withPython.YoucanaccessIDLEonthesamefolderwhereyoufoundthecommandlineiconoronthestartmenu.AssoonasyouclickontheIDLEicon,itwilltakeyoutothePythonShellwindow.

ThePythonShellWindow

The Python ShellWindow has dropdownmenus and a >>>prompt that you have seenearlier in the command line window. Here you can type and enter statements orexpressionsforevaluationinthesamewaythatyouusedthecommandlineearlier.Thistimehowever,IDLE’seditingmenuallowsyoutoscrollbacktoyourpreviouscommands,cut, copy, and paste previous statements andmakemodifications. IDLE is quite a leapfromthecommandlineinteraction.

The Python Shell window has the following menu items: File, Edit, Shell, Debug,Options,Windows,andHelp.

The Shell and Debugmenus provide capabilities youwould find useful when creatinglargerprograms.

TheShellmenuallowsyou to restart theshellorsearch theshell’s log to find themostrecentreset.

TheDebugMenuhasusefulmenu items for tracing the source fileofanexceptionandhighlighting the erring line. TheDebugger optionwill usher in an interactive debuggerwindowthatwillallowyoutostepthroughtherunningprogram.TheStackVieweroptiondisplaysthecurrentPythonstackthroughanewwindow.

The Options window allows you to configure IDLE to suit your Python workingpreferences.

TheHelpoptionopensPythonHelpanddocumentation.

TheFileWindow

The items on the File menu allows you to create a new file, open an old file, open amodule,and/orsaveyoursession.Whenyouclickonthe‘NewFile’option,youwillbetakentoanewwindow,asimpleandstandardtexteditorwhereyoucantypeoredityourcode.Initially,thisfilewindowisnamed‘untitled’butitsnamewillsoonchangeasyousaveyourcode.

TheFilewindow’smenubarvariesonlyslightlywiththeShellWindow.Itdoesn’thavethe ‘Shell’ and ‘Debug’ menu found in the Shell Window but it introduces two newmenus: theRun and the Formatmenu.When you choose toRun your code on the filewindow,youcanseetheoutputontheShellWindow.

TheScriptMode

Whenworkinginscriptmode,youwon’tautomaticallyseeresultsthewayyouwouldininteractive mood. To see an output from a script, you’ll have to run the script and/orinvoketheprint()functionwithinyourcode.

Chapter4PythonSyntax

Python syntax refers to the set of rules that defines how human users and the systemshouldwriteandinterpretaPythonprogram.IfyouwanttowriteandrunyourprograminPython,youmustfamiliarizeyourselfwithitssyntax.

Keywords

Python keywords are reserved words in Python that should not be used as variable,constant, functionname,or identifier inyour code.Takenoteof thesekeywords if youdon’twanttorunintoerrorswhenyouexecuteyourprogram:

andassert

breakclass

continuedef

delelif

elseexcept

execfinally

forfrom

globalif

importin

islambda

notor

passprint

raisereturn

trywhile

withyield

PythonIdentifiers

APythonIdentifierisanamegiventoafunction,class,variable,module,orotherobjectsthatyou’llbeusinginyourPythonprogram.Anyentityyou’llbeusinginPythonshouldbeappropriatelynamedoridentifiedastheywillformpartofyourprogram.

HerearePythonnamingconventionsthatyoushouldbeawareof:

Anidentifiercanbeacombinationofuppercaseletters,lowercaseletters,underscores,and digits (0-9). Hence, the following are valid identifiers: myClass, my_variable,var_1,andprint_hello_world.

Specialcharacterssuchas%,@,and$arenotallowedwithinidentifiers.An identifier should not begin with a number. Hence, 2variable is not valid, butvariable2isacceptable.

Python is a case-sensitive language and this behavior extends to identifiers. Thus,LaborandlaboraretwodistinctidentifiersinPython.

YoucannotusePythonkeywordsasidentifiers.

Classidentifiersbeginwithanuppercaseletter,buttherestoftheidentifiersbegininlowercase.

Youcanuseunderscorestoseparatemultiplewordsinyouridentifier.

Youshouldalwayschooseidentifiers thatwillmakesense toyouevenaftera longgap.Hence,while it iseasy to setyourvariable toc=2,youmight find itmorehelpful forfuturereferenceifyouusealongerbutmorerelevantvariablenamesuchascount=2.

UsingQuotations

Pythonallows theuseofquotationmarks to indicate string literals.Youcanuse single,double, or triple quotes but youmust start and end the stringwith the same type.Youwouldusethetriplequoteswhenyourstringrunsacrossseverallines.

PythonStatements

StatementsareinstructionsthataPythoninterpretercanexecute.Whenyouassignavalueto a variable, say my_variable = “dog”, you’re making an assignment statement. Anassignmentstatementmayalsobeasshortasc=3.ThereareotherkindsofstatementsinPython,likeifstatements,whilestatements,forstatements,etc.

Multi-linestatements

Astatementmayspanover several lines.Tobreaka longstatementovermultiple lines,youcanwraptheexpressioninsideparentheses,braces,andbrackets.Thisisthepreferredstyleforhandlingmulti-lineexpressions.Anotherwaytowrapmultiplelinesisbyusingabackslash(\)attheendofeverylinetoindicatelinecontinuation.

Indentation

WhilemostprogramminglanguagessuchasJava,C,andC++usebracestodenoteblocksofcode,Pythonprogramsarestructuredthroughindentation.InPython,blocksofcodesaredefinedby indentationnotasamatterof styleorpreferencebutasa rigid languagerequirement.ThisprinciplemakesPythoncodesmorereadableandunderstandable.

AblockofcodecanbeeasilyidentifiedwhenyoulookataPythonprogramastheystarton the same distance to the right. If it has to bemore deeply nestled, you can simplyindent another block further to the right. For example, here is a segment of a programdefiningcar_rental_cost:

defcar_rental_cost(days):

cost=35*days

ifdays>=8:

cost-=70

elifdays>=3:

cost-=20

returncost

Youhavetomakesurethat theindentspaceisconsistentwithinablock.WhenyouuseIDLEandotherIDEstoinputyourcodes,Pythonintuitivelyprovidesindentationonthesubsequent line when you enter a statement that requires indentation. Indentation, byconvention,isequivalentto4spacestotheright.

Comments

When writing a program, you’ll find it helpful to put some notes within your code todescribewhatitdoes.Acommentisveryhandywhenyouhavetorevieworrevisityourprogram.Itwillalsohelpanotherprogrammerwhomightneedtogooverthesourcecode.Youcanwritecommentswithinyourprogrambystartingthelinewithahash(#)symbol.A hash symbol tells the Python interpreter to ignore the comment when running yourcode.

For multi-line comments, you can use a hash symbol at the beginning of each line.Alternatively,youcanalsowrapmulti-linecommentwithtriplequotes.

Chapter5VariablesandDataTypes

Variables

Avariableislikeacontainerthatstoresvaluesthatyoucanaccessorchange.Itisawayofpointingtoamemorylocationusedbyaprogram.Youcanusevariablestoinstructthecomputertosaveorretrievedatatoandfromthismemorylocation.

Python differs significantly from languages such as Java, C, or C++when it comes todealingwithvariables.Otherlanguagesdeclareandbindavariabletoaspecificdatatype.Thismeansthatitcanonlystoreauniquedatatype.Hence,ifavariableisofintegertype,youcanonlysaveintegersinthatvariablewhenrunningyourprogram.

Pythonisalotmoreflexiblewhenitcomestohandlingvariables.Ifyouneedavariable,you’ll just thinkofanameanddeclare itbyassigningavalue. Ifyouneed to,youcanchangethevalueanddatatypethatthevariablestoresduringprogramexecution.

Toillustratethesefeatures:

InPython,youdeclareavariablebygivingitavalue:

my_variable=10

Take note thatwhen you are declaring a variable, you are not stating that the variablemy_variable isequal to10.What thestatementactuallymeans is“my_variable isset to10”.

Toincreasethevalueofthevariable,youcanenterthisstatementonthecommandline:

>>>my_variable=my_variable+3

To see how Python responded to your statement, invoke the print command with thisstatement:

>>>print(my_variable)

You’llseethisresultonthenextline:

13

To use my_variable to store a literal string “yellow”, you’ll simply set the variable to“yellow”:

>>>my_variable=“yellow”

Toseewhat’scurrentlystoreinmy_variable,usetheprintcommand:

>>>print(my_variable)

Onthenextline,you’llsee:

yellow

DataTypes

Pythonhandlesseveraldatatypestofacilitatetheneedsofprogrammersandapplicationdevelopers forworkabledata.These include strings,numbers,Booleans, lists, date, andtime.

Strings

A string is a sequence of Unicode characters that may be a combination of letters,numbers,andspecialsymbols.TodefineastringinPython,youcanenclosethestringinmatchingsingleordoublequotes:

>>>string1=“Iamenclosedinsinglequotes.”

>>>string2=“Iamenclosedindoublequotes.”

Ifaliteralstringenclosedinsinglequotescontainsasinglequote,you’llhavetoplaceabackslash(\)beforethesinglequotewithinthestringtoescapethecharacter.Forexample:

>>>string3=‘Itdoesn'tlookgoodatall.’

Toprintstring3:

>>>print(string3)

Itdoesn’tlookgoodatall.

Ofcourse,youwouldn’thavetodothisifyouuseddoublequotestoenclosethestring:

>>>string3=“Itdoesn’tseemnice”

Similarly,you’llhavetoplaceabackslashbeforeadoublequoteifyourstringisenclosedindoublequotes:

>>>txt=“Hesaid:\“Youshouldgetthesameresultsnomatterhowyouchoosetoencloseastring.\””

>>>print(txt)

Hesaid:“Youshouldgetthesameresultsnomatterhowyouchoosetoencloseastring.”

Stringsmaybeindexedorsubscripted.InPython,indexingstartsfrom0(zero)insteadof1.Hence,astring’sfirstcharacterhasazeroindex.

ToillustratehowstringindexingworksinPython,definethestring“HelloPython”onthecommandline:

>>>s=“HelloPython”

ThisishowPythonwouldindexthestring:

-12 -11 -10 -9 -8 -6 -6 -5 -4 -3 -2 -1

H e l l o P y t h o n

0 1 2 3 4 5 6 7 8 9 10 11

To access the first character on the string you just created, type and enter the variablenamesandtheindex0withinsquarebracketslikethis:

>>>s[0]

You’llgetthisoutput:

‘H’

Accessingthefirstcharacteriseasybecauseyouknowthatitsindexnumberiszero.Youdonothavethisadvantagewhenyouwanttoaccessthelastcharacteronthestring.

Toaccessthelastcharacter,youcanusethisexpression:

>>>s[len(s)-1]

You’llgettheoutput:

‘n’

The expression introduces you to the len function. There is actually an easier way toaccessthelastitemonthestring:

>>>s[-1]

‘n’

Toaccessthepenultimatecharacter:

>>>s[-2]

‘o’

Besidesindexing,youcanuseotherfunctionsandmathematicaloperatorsonastring.

ConcatenatingStrings

Strings can be added together with plus (+) operator. To concatenate the string “HelloPython”:

>>> “Hello”+“Python”

‘HelloPython’

RepeatingStrings

Youcaneasilyrepeatstringsoritsconcatenationwiththe*operator.Forexample:

Entering“**^**”*5willyield:

‘**^****^****^****^****^**’

You’llgetthesameresultwiththis:

>>>s=“**^**”

>>>s*5

‘**^****^****^****^****^**’

GettingtheSizeofStrings

Youcangetthesizeofastringwiththelen()function.Forexample,togetthesizeofthestring“World”:

>>>len(“World”)

5

SlicingStrings

Youcancreatesubstringswiththeslicingnotation.Youcandothisbyplacingtwoindices(separated by a colon) within square brackets. The first index marks the start of thesubstringwhile the second index indicates the index number of the first character youdon’twanttoincludeinthesubstring.

Forexample:

>>>“Program”[3:5]

willresultin:

‘gr’

>>>“Program”[3:6]

willyield:

‘gra’

Another way of doing this is by storing “Program” to a variable andmanipulating thevariabletoproducethedesiredresult:

>>>p=“Program”

>>>p[3:6]

‘gra’

Ifyouwantthesubstringtostartfromacharactertotheendoftheoriginalstring,youcanjustomitthesecondindex.Forexample:

>>>p=“Program”

>>>p[4:]

‘ram’

Conversely, if you want your substring to start from the first character of the originalstring,youcanomitthefirstindexandwritethelastindextobeincludedonthesubstring.Forexample:

>>>p=“Program”

>>>p[:4]

‘Prog’

Thelower()andupper()function

Ifyouhaveastringlike“GrandRiver”andyouhavedecidedthatyouneedyourdatatobeallinlowercase,youcanusethelower()functiontoprintthestringinlowercase.

Example:

>>>c=“GrandRiver”

>>>print(c.lower())

grandriver

Supposingyouneedyoustringtobeallcapitalized,youcaninvoketheupper() functiontoprintthestringinuppercase.

Example:

>>>print(c.upper())

GRANDRIVER

Thestr()method

Thestr()functionmakesstringsoutofnon-stringscharacter.Thisallowsprogrammerstoprintnon-stringcharactersas if theyarestringcharacters.This isveryhandywhenyouwant,forinstance,toprintanintegeralongwithstrings.

Example:

>>>pi=3.1416

>>>str(pi)

‘3.1416’

>>>print(“Thismyfavoritenumber:”+str(pi))

Thismyfavoritenumber:3.1416

Numbers

NumericDataTypes

OneofthemanyconveniencesofusingPythonisthatyoudon’treallyhavetodeclareanumericvaluetodistinguishits type.Pythoncanreadilytellonedatatypefromanotherwhenyouwriteandrunyourstatement.Ithasfourbuilt-innumericdatatypes.Python3supportsthreetypes:integer,floating-pointnumbers,andcomplexnumbers.Longintegers(‘long’)nolongerformaseparategroupofintegersbutareincludedinthe‘int’orintegercategory.

1. Integer(int)

Integers arewhole numberswithout decimal point.They canbe positive or negative aslongastheydon’tcontainadecimalpointthatwouldmakeanumberafloatingnumber,adistinctnumerictype.IntegershaveunlimitedsizeinPython3.

ThefollowingnumbersandliteralsarerecognizedbyPython:

Regularintegers

Examples:793,-254,4

Octalliterals(base8)

Toindicateanoctalnumber,youwillusetheprefix0oor0O(zerofollowedbyeitheralowercaseoruppercaseletter‘o’).

Example:

>>>a=0O7

>>>print(a)

7

Hexadecimalliterals(base16)

Toindicatehexadecimalliterals,youwillusetheprefix‘0X’or‘0x”(zeroanduppercaseorlowercaseletter‘x’).

Example:

>>>hex_lit=0xA0C

>>>print(hex_lit)

2572

Binaryliterals(base2)

To signify binary literals, you’ll use the prefix ‘0B’ or ‘0b’ (zero and uppercase orlowercase‘b’).

Example:

>>>c=0b1100

>>>print(c)

12

ConvertingIntegerstotheirStringRepresentation

Earlier, you have seen how the print command converted literals to their equivalent inintegers.Pythonmakes it possible foryou towork theotherwayaroundby converting

integerstotheirliteralrepresentation.Toconvertanintegerintoitsstringrepresentation,youcanusethefunctionshex(),bin(),andoct().

Examples:

Toconverttheinteger7toitsoctalliteral,typeandenteroct(7)onthecommandprompt.You’llgettheoutput‘0o7’:

>>>oct(7)

‘0o7’

Hereiswhathappenswhenyouconverttheinteger2572toahexadecimalliteral:

>>>hex(2572)

‘0xa0c’

Finally,seewhathappenswhenyouusethebin()functiontoconverttheinteger12toitsbinarystring:

>>>bin(12)

‘0b1100’

Youcanstoretheresulttoavariablebydefiningavariablewiththehex(),bin(),andoct()functions:

Forexample:

>>>x=hex(2572)

>>>x

‘0xa0c’

To see the object type created and stored in the variable x, you can use and enter thecommandtype():

>>>type(x)

Youshouldgetthisresult:

<class‘str’>

2. Floating-pointnumbers

Alsoknownasfloats,floating-pointnumberssignifyrealnumbers.Floatsarewrittenwithadecimalpointthatsegregatestheintegerfromthefractionalnumbers.Theymayalsobewritteninscientificnotationwheretheuppercaseorlowercaseletter‘e’signifiesthe10thpower:

>>>6.2e3

6200.0

>>>6.2e2

620

3. Complexnumbers

Complexnumbersarepairsofrealandimaginarynumbers.Theytaketheform‘a+bJ’where‘a’isafloatandtherealpartofthecomplexnumber.OntheothersideisbJwhere‘b’isafloatandJoritslowercaseindicatesthesquarerootofanimaginarynumber,-1.Thismakes‘b’theimaginarypartofthecomplexnumber.

Hereareexamplesofcomplexnumbersatwork:

>>>a=2+5j

>>>b=4–2j

>>>c=a+b

>>>print(c)

(6+3j)

ComplexnumbersarenotextensivelyusedinPythonprogramming.

ConversionofNumberType

YoucanexpectPythontoconvertexpressionswithmixedtypesofnumberstoacommontype to facilitate evaluation. In some situations, however, youmayhave to convert onenumber type to another explicitly, like when the conversion is required by a functionparameter.Youcantypethefollowingexpressionstoconvertanumbertoanothertype:

Toconvertxtoafloat:>>>float(x)

Example:

>>>float(12)

12.0

Toconvertxtoaplaininteger:int(x)

>>>int(12)

12

Toconvertxtoacomplexnumber:typecomplex(x)

>>>complex(12)

(12+0j)

DateandTime

Most applications require date and time information to make it work efficiently andeffectively.InPython,youcanusethefunctiondatetime.now()toretrievethecurrentdateand time.Thecommanddatetime.now()callsonabuilt-inPythoncodewhichgives thecurrentdateandtime.

TogetthedateandtimefromPython,encodethefollowingonthecommandprompt:

>>>fromdatetimeimportdatetime

>>>datetime.now()

datetime.datetime(2016,3,10,2,16,19,962429)

Thedateandtimeinthisformatisalmostunintelligibleandyoumightwanttogetaresultthat ismore readable.Oneway todo this is byusing ‘strftime’ fromPython’s standardlibrary.

Tryenteringthesecommandsandseeifyou’llgettheformatyoulike.

>>>fromtimeimportstrftime

>>>strftime(“%Y-%m-%d%H:%M:%S”)

‘2016-03-1002:20:03’

BooleanDataType

Comparisons inPythoncanonlygenerateoneof twopossible responses:TrueorFalse.Thesedatatypesarecalledbooleans.

Toillustrate,youcancreateseveralvariablestostoreBooleanvaluesandprinttheresult:

bool_1=4==2*3

bool_2=10<2*2**3

bool_3=8>2*4+1

print(bool_1)

print(bool_2)

print(bool_3)

ThePythonShellwilldisplaytheseresults:

False

True

False

Lists

A list is a data type that can be used to store any type and number of variables andinformation.

Youcandefineandassignitemstoalistwiththeexpression:

my_list=[item_1,item_2,item_3]

Pythonalsoallowscreationofanemptylist:

my_list=[]

Toillustrate,let’screatealistofcolors:

colors=[“red”,“orange”,“yellow”,“green”,“indigo”,“white”]

Sincethisisanindexedlist,thefirstitemoncolorshaszeroasitsindex.

Toaccessthefirstitemonthelist,youcanprintthecolorwiththecommand:

>>>print(colors[0])

red

Toprintthecolornameofthethirdcoloronthelist,youcanenter:

>>>print(colors[4])

indigo

Toseehowmanycolorsareonthelist,youcanusethelen()function:

>>>len(colors)

6

Thereareonlysixcolorsonyourlistbutyouwanttohaveallsevencolorsoftherainbowin your list. To seewhat colors are on the list, you can use the print to seewhat colormightbemissing:

>>>print(colors)

[‘red’,‘orange’,‘yellow’,‘green’,‘indigo’,‘white’]

Itappearsthatthecolorslistdoesn’tjustlackonecolorname.Italsohasonememberthatshouldnothavebeenincluded–‘white’.Toremove‘white’fromthelist,youcanusetheremove()method:

>>>colors.remove(“white”)

Youcanviewtheupdatedlistwiththeprintcommand:

>>>print(colors)

[‘red’,‘orange’,‘yellow’,‘green’,‘indigo’]

Thelistisstillshortof2colors–violetandblue.

Toaddviolettoyourcolorslist,youcanusetheappendcommand:

>>>colors.append(“violet”)

Let’scheckouttheupdatedlistwiththeprintcommand:

>>>print(colors)

[‘red’,‘orange’,‘yellow’,‘green’,‘indigo’,‘violet’]

Thecolor‘violet’wasaddedtotheendofthelist.Now,youonlyneedtoaddonemorecolor-blue.Let’ssayyouwanttohave‘blue’insertedbetween‘green’and‘indigo’.

YoucanusePython’sinsert()methodwiththesyntax:

list.insert(index,obj)

Theparametersareindexandobject.Indexreferstothepositionwhereyouwantthenewitemtobelocated.Theobjectistheitemyouwanttoinsert.

Applyingthesyntaxtotheaboveexample,you’llhavethecommand:

>>>colors.insert(4,“blue”)

Toseethenewlist:

>>>print(colors)

[‘red’,‘orange’,‘yellow’,‘green’,‘blue’,‘indigo’,‘violet’]

Slicinglists

Youcanalsoslicelistsinthesamewaythatyouslicestrings.

For example, if you onlywant to display the colors ‘green’, ‘blue’, and ‘indigo’, withindexof3,4,5respectively,youcanusethiscommand:

>>>colors[3:6]

[‘green’,‘blue’,‘indigo’]

Dictionary

Adictionary is likea listbut insteadof lookingupan index toaccessvalues,you’llbeusing a unique key, which can be a number, string, or tuple. Dictionary values can beanythingbut thekeysmustbeanimmutabledata type.Acolonseparatesakeyfromitsvalueandallareenclosedincurlybraces.Hereisthedictionarystructure:

d={key_1:a,key_2:2,key_3:ab}

Anemptydictionarywillhavethisformat:

d={}

Adictionarycanbeaveryusefultoolforstoringandmanipulatingkey-valuepairssuchasthoseusedinphonebooks,directory,menu,orlog-indata.Youcanadd,modify,ordeleteexistingentrieswithinthedictionary.

Toseehowdictionariesactuallywork,youcancreateadictionarynamedmenuwithdishandpricespairs:

menu={“spam”:12.50,“carbonara”:20,“salad”:15}

To see how many key-value pairs are stored in the dictionary, you can use the len()function:

>>>len(menu)

3

Toprintthecurrententriesinthemenudictionary:

>>>print(menu)

{‘salad’:15,‘carbonara’:20,‘spam’:12.5}

Toaddanotherentryinthemenudictionary,youcanusethisformat:

d[key_4:b]

Applyingthisstructuretothemenudictionary,youcanaddthedish-priceentryofcake:6with:

menu[“cake”]=6

Toseetheupdatedmenu,usetheprintcommand:

>>>print(menu)

{‘spam’:12.5,‘cake’:6,‘carbonara’:20,‘salad’:15}

Assumingyounolongerwanttoincludespaminyourmenu,youcaneasilydosowiththedelcommand:

>>>delmenu[“spam”]

Toseethemodifiedlistafterdeletingspam:

{‘cake’:6,‘carbonara’:20,‘salad’:15}

Youmightwant tochange thevalues inanyof thekeysatonepoint.For instance,youneedtochangethepriceofcarbonarafrom20to22.Todothat,you’lljustassignanewvaluetothekeywiththiscommand:

>>>menu[“carbonara”]=22

Youcanusetheprintcommandoncemoretoseetheupdatedmenu:

>>>print(menu)

{‘cake’:6,‘carbonara’:22,‘salad’:15}

Ifyouwanttoremoveallentriesinthedictionary,youcanusethefunction

dict.clear()

Toclearallentriesinthemenu:

>>>dict.clear(menu)

Usetheprintcommandtoseewhathappenedtothemenudictionary:

>>>print(menu)

{}

The Python Shell displayed an empty dictionary with the clear command. Now that itcontainsnodataatall,youmightdecidetodeletethedictionary.Youcandosowiththedelcommand:

deldict

Todeletethemenudictionary:

delmenu

Toseewhathappened,usetheprintcommand.

>>>print(menu)

Traceback(mostrecentcalllast):

File“<pyshell#19>”,line1,in<module>

print(menu)

NameError:name‘menu’isnotdefined

Yougotanerrormessagebecausemenunolongerexists.

Chapter6PythonBasicOperators

Pythonoperatorsallowprogrammerstomanipulatedataoroperands.HerearethetypesofoperatorssupportedbyPython:

ArithmeticOperatorsAssignmentOperatorsRelationalorComparisonOperatorsLogicalOperatorsIdentityOperatorsBitwiseOperatorsMembershipOperators

ArithmeticOperators

Pythondoesagoodjobofprocessingmathematicalexpressionswithitsbasicarithmetic

operators.Youcaneasilymakeprogramstoautomatetaskssuchascomputingtax,tips,discounts,orrent.

+ Addition addsthevalueoftheleftandrightoperands

- Subtractionsubtractsthevalueoftherightoperandfromthevalueoftheleftoperand

* Multiplication multipliesthevalueoftheleftandrightoperand

/ Divisiondividesthevalueoftheleftoperandbytherightoperand

** Exponent performsexponentialcalculation

% Modulusreturnstheremainderafterdividingtheleftoperandwiththerightoperand

//FloorDivision

divisionofoperandswherethesolutionisaquotientleftafterremovingdecimalnumbers

Addition, subtraction,multiplication, and division are themost basic operators and areinvokedbyenteringthefollowingexpressions:

Addition:

>>>1+3

4

Subtraction:

>>>10–4

6

Multiplication:

>>>4*2

8

Division:

>>>10/2

5.o

Exponent

Exponentialcalculationisinvokedbyraisingthefirstnumbertothepowerdefinedbythenumberafterthe**operator:

>>>2**32raisedtothepowerof3

8

Modulus

Themodulusoperatorgivestheremainderafterperformingdivision:

>>>17%5

2

FloorDivision

Floordivision,ontheotherhand,returnsthequotientafterremovingfractionalnumbers:

>>>17//5

3

UsingBasicOperatorstoComputeSalesTax,Tip,andTotalBill

Toputyourknowledgeofvariables,datatypes,andoperatorstogooduse,youcandesignasimpleprogramthatwillcomputethesalestaxandtiponarestaurantmeal.

Mealcost$65.50

Salestaxrate6.6%

Tip20%ofmeal+tax

First,setupavariablemealtostorethefoodcost:

meal=65.50

Next, set up the tax and tip variable. Assign both variables the decimal value of thepercentagesgiven.Youcandothisbyusing100asdivisor.

tax=6.6/100

tip=20/100

Yourtipisbasedonmealcostandtheaddedsalestaxsoyouneedtogetthetotalamountofthemealandthesalestax.Onewaytodothisisbysimplycreatinganewvariabletostorethetotalcostofthemealandtax.Anotherwayisbyreassigningthevariablemealsothatitstoresbothvalues:

meal=meal+meal*tax

Nowthatyouhavereassignedmealtotakecareofthemealcostandtax,you’rereadytocompute for the tip.This time,youcan set anewvariable to store thevalueof the tip,meal,andtax.Youcanusethevariabletotaltoholdallvalues:

total=meal*tip

Here’syourcodetocomputeforthetotalbillamount:

meal=65.50

tax=6.6/100

tip=20/100

meal=meal+meal*tax

total=meal+meal*tip

Ifyou’reusingthefileeditorinIDLE,youcansavethefileinafilenameofyourchoiceandPythonautomatically appends the .pyextension.Asyoumayhavenoticed, the fileeditorwillalwayspromptyoutosaveyourfilebeforeitdoesanythingaboutyourcode.Just like when naming other data files and types, you should use a filename that’sdescriptiveofthefile.Inthiscase,afilenamelikeBillCalculatorshoulddothetrick.

Togetthetotalamount,gotothePythonShellandtypetotal:

>>>total

83.78760000000001

Nowyouhavethebillamount:83.78760000000001

Ifyou’reusingthelinecommandwindow,youcansimplyentertheabovecodeonaperlinebasis.

ThissimpleprogramshowshowstraightforwardPythonprogrammingisandhowusefulitcouldbeinautomatingtasks.Nexttimeyoueatout,youcanreusetheprogrambysimplychangingthefiguresonyourbillcalculator.Thinkforwardandvisualizehowconvenientit couldbe if you couldput your code in a bigger program thatwill simply askyou toinputthebillamountinsteadofaccessingtheoriginalcode.YoucandothatwithPython.

AssignmentOperators

Theseoperatorsareusefulwhenassigningvaluestovariables:

Operators Function

= assignsthevalueoftherightoperandtotheleftoperand

+=addandaddsthevalueoftherightandleftoperandandassignsthetotaltotheleftoperand

-=subtractand

deductsthevalueoftherightoperandfromthevalueoftheleftoperandandassignsthenewvaluetotheleftoperand

*=multiplyand

multipliestheleftandrightoperandandassignstheproducttotheleftoperand

/=divideand

dividestheleftoperandwiththevalueoftherightoperandandassignsthequotienttotheleftoperand

**=exponent

performsexponentialoperationontheleftoperandandassignstheresulttotheleftoperand

//=floordivisionand

performsfloordivisionontheleftoperandandassignstheresulttotheleftoperand

=Operator

Youhaveseenthisoperatoratworkinpreviouschapterswhenyouhaveassigneddifferentvaluestovariables.Examples:

a=c

a=b+c

a=8

a=8+6

s=“IlovePython.”

+=addand

The‘addand’(+=)operatorissimplyanotherwaytoexpressx=x+asothatyou’llendupwiththestatementx+=a.

-=subtractand

The‘subtractand’(-=)operatorisequivalenttotheexpressionx=x–aandisexpressedwiththestatementx-=a

*=multiplyand

The ‘multiply and’ (*=) operator is the equivalent of the statement x = x * a and isexpressedwithx*=a.

/=divideand

The‘divideand’(/=)operator is likesayingx=x/aandisexpressedwiththestatementx/=a.

%=modulusand

The‘modulusand’ (%=)operator isanotherway tosayx=x%awhereyou’llendupinsteadwiththeexpressionx%=a.

//=floordivisionand

The‘floordivisionand’isequivalenttotheexpressionx=x//aandtakestheformx//=a.

RelationalorComparisonOperators

Relationaloperatorsevaluatevalueson the leftandrightsideof theoperatorandreturntherelationaseitherTrueorFalse.

HerearetherelationaloperatorsinPython:

Operator Meaning

== isequalto

< islessthan

> isgreaterthan

<= islessthanorequalto

>= isgreaterthanorequalto

!= isnotequalto

Examples:

>>>8==6+2

True

>>>6!=6

False

>>>-1>0

False

>>>7>=5

True

LogicalOperators

Pythonsupports3logicaloperators:

or

and

not

xoryIfthefirstargument,x,isfalse,thenitevaluatesthesecondargument,y.Else,itevaluatesx.

xandyIfxisfalse,thenitevaluatesx.Else,ifxistrue,itevaluatesy.

notxIfxisfalse,thenitreturnsTrue.Ifxistrue,itreturnsFalse.

Examples:

>>>(8>9)and(2<9)

False

>>>(2>1)and(2>9)

False

>>>(2==2)or(9<20)

True

>>>(3!=3)or(9>20)

False

>>>not(8>2)

False

>>>not(2>10)

True

PrecedenceofPythonOperators

Pythonoperatorsareevaluatedaccordingtoasetorderorpriority:

Description Operators

1 Exponentiation **

2Ccomplement,unaryplus,andminus

~,+,-

3Multiplication,division,modulo,andfloordivision

*,/,%,//

4 additionandsubtraction +-

5 Rightandleftbitwiseshift >>,<<

6 Bitwise‘AND’ &

7Regular`OR’andBitwiseexclusive‘OR’

|,^

8 Comparisonoperators <=<>>=

9 Equalityoperators ==!=

10 Assignmentoperators =,+=,-=,*-,/=,%=//=**=

11 Identityoperators is,isnot

12 Membershipoperators in,notin

13 Logicaloperators or,and,not

Chapter7Python’sBuilt-inFunctions

Functionsprovideefficiencyandstructuretoaprogramminglanguage.Pythonhasmanyusefulbuilt-infunctionstomakeprogrammingeasier,faster,andmorepowerful.

Theinput()Function

Programs usually require input that can come from different sources: keyboard,mouseclicks, database, another computer’s storage, or the internet. Since the keyboard is themost commonway to gather input, Python provided its users the input() function.Thisfunctionhasanoptionalparametercalledthepromptstring.

Oncetheinputfunctioniscalled,thepromptstringwillbedisplayedonthescreenandtheprogramflowstopsuntil theuserhasenteredaninput.Theinputis theninterpretedandtheinput()functionreturnstheuser’sinputasastring.

Toillustrate,hereisasampleprogramthatcollectskeyboardinputfornameandage:

name=input(“MayIknowyourname?“)

print(“It’sapleasuretomeetyou”+name+“!”)

age=input(“Yourage,please?“)

print(“So,you’re”+age+”yearsold,”+name+“!”)

Beforeyousavethecode,takeacloselookatthestringtobeprintedonthesecondline.You’llnoticethatthereisablankspaceafter‘you’andbeforethedoublequote.Thisspaceensures that there will be a space between ‘you’ and the ‘name’ input when the printcommand is executed. The same convention can be seen on the 4th line with the printcommandwhere‘you’re’isseparatedbyasinglespacefromthe‘age’inputand‘old’isseparatedbyaspacefromthe‘name’input.

Savethecodeasinfo_input.pyandrunit.

ThePythonShellwilldisplaythestringonthefirstline:

MayIknowyourname?

Aresponseisneededatthispointandtheprogramstopsexecutinguntilakeywordinputisobtained.Let’stypeandenterthenameJefftoseewhathappens:

It’sapleasuretomeetyouJeff!

Yourage,please?

Theprogramhasnowproceededtothenextinputfunctionandiswaitingforthekeyboardinput.Let’senter22asJeff’sageandseewhattheprogramdoesnext:

So,you’re22yearsold,Jeff!

The program printed the last string on the program after a keyboard response wasobtained.HereistheentireoutputonthePythonShell:

MayIknowyourname?Jeff

It’sapleasuretomeetyouJeff!

Yourage,please?22

So,you’re22yearsold,Jeff!

Therange()function

Pythonhasamoreefficientwaytohandleaseriesofnumbersandarithmeticprogressionsandthis isbyusingoneitsbuilt-infunctions:range().Therangefunctionisparticularlyusefulin‘forloops’.

Hereisanexampleoftherange()function:

>>>range(5)

range(0,5)

Theexpressionrange(5)abovegeneratesaniteratorthatprogressesintegersfromzeroandendswith4(5-1).Toshowthelistofnumbers,youcanusethecommandlist(range(n)):

>>>list(range(5))

[0,1,2,3,4]

Youcanexercisemorecontroloverthelistoutputbycallingtherange()functionwithtwoarguments:

range(begin,end)

Example:

>>>range(5,9)

range(5,9)

Toshowthelist:

>>>list(range(5,9))

[5,6,7,8]

Theaboveexamplesofrange()demonstratedanincrementof1.YoucanchangethewayPython increments the number by introducing a third argument, the ‘step’. It can be anegativeorpositivenumber,butneverzero.

Hereistheformat:

range(begin,end,step)

Example:

>>>range(10,71,5)

range(10,71,5)

Invokinglist,we’llseethissequenceofnumbers:

>>>list(range(10,71,5))

[10,15,20,25,30,35,40,45,50,55,60,65,70]

Theprint()Function

Python3turnedprintfromastatementintoafunction.Hence,youmustalwaysencloseyourprintparameterswithintheroundparentheses.

Examples:

print(“ThisisPython3printfunction)

print(s)

print(5)

Theprint()functioncanprintanynumberofvalueswithintheparentheses;theymustbeseparatedbycommas.Forexample:

a=3.14

b=“age”

c=32

print(“a=“,a,b,c)

Theresult:

a=3.14age32

ThePythonshelldisplayedvalueswithblankspacesbetweenthem.

abs()

Theabs()functionreturnstheabsolutevalueofasinglenumber.Ittakesanintegerorfloatnumberasargumentandalwaysreturnsapositivevalue.

Examples:

>>>abs(-10)

10

>>>abs(5)

10

Whencomplexnumbersareusedasargument,theabs()functionreturnsitsmagnitude:

>>>abs(3+4j)

5.0

max()

Themax()functiontakestwoormoreargumentsandreturnsthelargestone.

Examples:

>>>max(9,12,6,15)

15

>>>max(-2,-7,-35,-4)

-2

min()

Themin()functiontakestwoormoreargumentsandreturnsthesmallestitem.

Examples:

>>>min(23,-109,5,2)

-109

>>>min(7,26,0,4)

0

type()

Thetype()functionreturnsthedatatypeofthegivenargument.

Examples:

>>>type(“Thisisastring”)

<class‘str’>

>>>type(12)

<class‘int’>

>>>type(2+3j)

<class‘complex’>

>>>type(215.65)

<class‘float’>

len()

Thelen()functionreturnsthelengthofanobjectorthenumberofitemsinalistgivenasargument.

Examples:

>>>len(“pneumonoultramicroscopicsilicovolcanoconiosi”)

44

>>>s=(“winter”,“spring”,“summer”,“fall”)

>>>len(s)

4

HereisalistofPhyton’sbuilt-infunctions:

abs() all() any()

ascii() bin() bool()

bytearray() bytes() callable()

chr() classmethod() compile()

complex() delattr() dict()

dir() divmod() enumerate()

eval() exec() filter()

float() format() frozenset()

getattr() globals() hasattr()

hash() help() hex()

id() __import__() input()

int() isinstance() issubclass()

iter() len() list()

locals() map() max()

memoryview() min() next()

object() oct() open()

ord() pow() print()

property() range() repr()

reversed() round() set()

setattr() slice() sorted()

staticmethod() str() sum()

super() tuple() type()

vars() zip()

Chapter8ConditionalStatements

Conditionalstatementsarecommonamongprogramminglanguagesandtheyareusedtoperformactionsorcalculationsbasedonwhetheraconditionisevaluatedastrueorfalse.If-then-else statements or conditional expressions are essential features of programminglanguagesandtheymakeprogramsmoreusefultousers.

Theif-then-elsestatementinPythonhasthefollowingbasicstructure:

ifcondition1:

block1_statement

elifcondition2:

block2_statament

else:

block3_statement

Thisstructurewillbeevaluatedas:

If condition1 is True, Python will execute block1_statement. If condition1 is False,condition2willbeexecuted.Ifcondition2isevaluatedasTrue,block2_statementwillbeexecuted.Ifcondition2turnsouttobeFalse,Pythonwillexecuteblock3_statement.

Toillustrate,hereisanif-then-elsestatementbuiltwithinthefunction‘your_choice’:

defyour_choice(answer):

ifanswer>5:

print(“Youareoveraged.”)

elifanswer<=5andanswer>1:

print(“WelcometotheToddler’sClub!”)

else:

print(“YouaretooyoungforToddler’sClub.”)

print(your_choice(6))




YouwillgetthisoutputonthePythonShell:

Youareoveraged.

None

WelcometotheToddler’sClub!

None

YouaretooyoungforToddler’sClub.

None


None

Conditionalconstructsmaybranchout tomultiple‘elif’branchesbutcanonlyhaveone‘else’branchattheend.Usingthesamecodeblock,anotherelifstatementmaybeinsertedtoprovideforprivilegedmemberoftheToddler’sclub:2year-oldkids.

defyour_choice(answer):

ifanswer>5:

print(“Youareoveraged.”)

elifanswer<=5andanswer>2:

print(“WelcometotheToddler’sClub!”)

elifanswer==2:

print(“Welcome!YouareastarmemberoftheToddler’sClub!”)

else:

print(“YouaretooyoungforToddler’sClub.”)






Youareoveraged.

None

WelcometotheToddler’sClub!

None


None


None

Welcome!YouareastarmemberoftheToddler’sClub!

None

Chapter9Loops

A loop is a programming construct that enables repetitive processing of a sequence ofstatements.Pythonprovidestwotypesofloopstoitsusers:the‘forloop’andthe‘whileloop’.The‘for’and‘while’loopsareiterationstatementsthatallowablockofcode(thebodyoftheloop)toberepeatedanumberoftimes.

TheForLoop

Pythonimplementsaniterator-based‘forloop’.Itisatypeof‘forloop’thatiteratesoveralistofitemsthroughanexplicitorimplicititerator.

Theloopisintroducedbythekeyword‘for’whichisfollowedbyarandomvariablenamewhichwillcontainthevaluessuppliedbytheobject.

ThisisthesyntaxofPython’s‘forloop’:

forvariableinlist:

statements

else:

statements

Hereisanexampleofa‘forloop’inPython:

pizza = [“NewYork Style Pizza”, “Pan Pizza”, “Thin n Crispy Pizza”, “Stuffed CrustPizza”]

forchoiceinpizza:

ifchoice==“PanPizza”:

print(“Pleasepay$16.Thankyou!”)

print(“Delicious,cheesy”+choice)

else:

print(“Cheesypanpizzaismyall-timefavorite!”)

print(“Finally,I’mfull!”)

Runthisandyou’llgetthefollowingoutputonPythonShell:

Delicious,cheesyNewYorkStylePizza

Pleasepay$16.Thankyou!

Delicious,cheesyPanPizza

Delicious,cheesyThinnCrispyPizza

Delicious,cheesyStuffedCrustPizza

Cheesypanpizzaismyall-timefavorite!

Finally,I’mfull!

Usingabreakstatement

A Python break statement ends the present loop and instructs the interpreter to startsexecutingthenextstatementaftertheloop.Itcanbeusedinboth‘for’and‘while’loops.Besides leading the program to the statement after the loop, a break statement alsopreventstheexecutionofthe‘else’statement.

To illustrate, a break statement may be placed right after the print function of the ‘ifstatement’:


forchoiceinpizza:



break

print(“Delicious,cheezy”+choice)

else:

print(“Cheezypanpizzaismyall-timefavorite!”)


ThePythonShellwillnowshow:

Delicious,cheezyNewYorkStylePizza


Finally,I’mfull!

UsingContinueStatement

Thecontinuestatementbringsbackprogramcontroltothestartoftheloop.Youcanuseitforboth‘for’and‘while’loops.

Toillustrate,thecontinuestatementmaybeplacedrightaftertheprintfunctionofthe‘forloop’toreplacethebreakstatement:


forchoiceinpizza:



continue

print(“Delicious,cheesy”+choice)

else:

print(“Cheesypanpizzaismyall-timefavorite!”)


Theoutputwillbe:

Delicious,cheesyNewYorkStylePizza


Delicious,cheesyThinnCrispyPizza

Delicious,cheesyStuffedCrustPizza

Cheesypanpizzaismyall-timefavorite!

Finally,I’mfull!

Usingtherange()FunctionwiththeforLoop

Therange()functioncanbecombinedwiththe‘forloop’tosupplythenumbersrequiredby the loop. In the following example, the range(1, x+1)provided thenumbers1 to50neededbythe‘forloop’toaddthesumof1until50:

x=50

total=0

fornumberinrange(1,x+1):

total=total+number

print(“Sumof1until%d:%d”%(x,total))

ThePythonShellwilldisplay:

l.py

Sumof1until50:1275

TheWhileLoop

APython‘whileloop’repeatedlycarriesoutatargetstatementwhiletheconditionistrue.

The loop iteratesas longas thedefinedcondition is true.When itceases tobe trueandbecomesfalse,controlpassestothefirstlineaftertheloop.

The‘whileloop’hasthefollowingsyntax:

whilecondition

statement

statement

Hereisasimple‘whileloop’:

counter=0

while(counter<10):

print(‘Thecountis:’,counter)

counter=counter+1

print(“Done!”)

Ifyourunthecode,youshouldseethisoutput:

l.py

Thecountis:0

Thecountis:1

Thecountis:2

Thecountis:3

Thecountis:4

Thecountis:5

Thecountis:6

Thecountis:7

Thecountis:8

Thecountis:9

Done!

UsingPassStatement

The pass statement tells the Python interpreter to ‘do nothing’. The interpreter simplycontinueswiththeprogram’sexecutionwheneverthepassstatementisencountered.ThisattributemakesitagoodplaceholderwheneverPythonsyntacticallyrequiresalinebuttheprogram itself does not require action. It can be very useful when you’re creating aprogramandyouneedtofocusonspecificareasofyourcode,butyoustillwanttoreservesomeloopsortestruntheincompletecode.

Hereishowyouwoulduseapassstatementtofillgapswithinacode:

deffunction_name(x):

pass

Chapter10User-DefinedFunctions

A function is a set of statements that perform a specific task, a common structuringelementthatallowsyoutouseapieceofcoderepeatedlyindifferentpartsofaprogram.The use of functions improve a program’s clarity and comprehensibility and makesprogrammingmore efficient by reducing code duplication and breaking down complextasks intomoremanageable pieces. Functions are also known as routines, subroutines,methods,procedures,orsubprograms.

Theycanbepassedasarguments,assignedtovariables,orstoredincollections.

Auser-definedPythonfunctioniscreatedordefinedbythedefstatementandfollowsthesyntax:

deffunction_name(parameterlist):

functionbody/statements

The indented statementsmake up the body of the function and are executedwhen thefunction iscalled.Once thefunction iscalled,parameters insideroundbracketsbecomearguments.

Functionbodiescanhavemorethanonereturnstatementwhichmaybeplacedanywherewithinthefunctionblock.Returnstatementsendthefunctioncallandreturnthevalueoftheexpressionafterthereturnkeyword.Areturnstatementwithnoexpressionreturnsthespecialvalue ‘None’. In theabsenceof a return statementwithin the functionbody, theendofthefunctionisindicatedbythereturnofthevalue‘None’.

The docstring is an optional statement after the function title which explains what thefunction does.While it is notmandatory, documenting your codewith a docstring is agoodprogrammingpractice.

HereisasimplefunctionthatprintsIlovePizza!

deflove_pizza():

print“IlovePizza!”

Hereisafunctionwithaparameterandreturnkeyword:

defabsolute_value(number):

ifnumber>=0:

returnnumber

else:

return-number

print(absolute_value(3))

print(absolute_value(-5))

Intheaboveexample,numberistheparameterofthefunctionabsolute_value.Itactsasavariablenameandholdsthevalueofapassedinargument.

Hereistheoutputwhentheabovecodeisrun:

3

5

Followingisafunctionwithanif-then-elsestatement.

defshutdown(yn):

ifyn.lower()==“y”:

return(“Closingfilesandshuttingdown”)

elifyn.lower()==(“n”):

return(“Shutdowncancelled”)

else:

return(“Pleasecheckyourresponse.”)

print(shutdown(“y”))

print(shutdown(“n”))

print(shutdown(“x”))

PythonShellwilldisplay:

Closingfilesandshuttingdown

Shutdowncancelled

Pleasecheckyourresponse.

Functioncantakemorethanoneparameterandusethemforcomputations:

defcalculator(x,y):

returnx*y+2

print(calculator(2,6))

print(calculator(3,7))

Runthecodeandyou’llgettheoutput:

14

23

Functionscancallotherfunctions

Functionscanperformdifferenttypesofactionssuchasdosimplecalculationsandprinttext.Theycanalsocallanotherfunction.

Forexample:

defmembers_total(n):

returnn*3

deforg_total(m):

returnmembers_total(m)+5

Toseewhatyoucodedoes,enterthefollowingprintcommands:

print(org_total(2))

print(org_total(5))

print(org_total(10))

You’llgettheseresults:

11

20

35

Scopeandlifetimeofalocalvariable

A variable’s scope refers to a program’s sectionswhere it is recognized. Variables andparametersdefinedwithinafunctionhavealocalscopeandarenotvisiblefromoutsideofthefunction.Ontheotherhand,avariable’slifetimereferstoitsperiodofexistenceinthememory. Its lifetime coincides with the execution of a function which ends when youreturnfromthefunction.Avariable’svalueisdiscardedoncethereturnisreachedandafunctionwon’tbeabletorecallavariable’svaluefromitspreviousvalue.

Chapter11ClassesandObject-OrientedProgramming

Pythonisanobject-orientedprogramminglanguage,whichmeansthatitmanipulatesandworkswithdatastructurescalledobjects.ObjectscanbeanythingthatcouldbenamedinPython – integers, functions, floats, strings, classes, methods, etc. These objects haveequalstatusinPython.Theycanbeusedanywhereanobjectisrequired.Youcanassignthem to variables, lists, or dictionaries. They can also be passed as arguments. EveryPythonobject is a class.Aclass is simplyawayoforganizing,managing, andcreatingobjectswiththesameattributesandmethods.

In Python, you can define your own classes, inherit from your own defined classes orbuilt-inclasses,andinstantiatethedefinedclasses.

ClassSyntax

Todefineaclass,youcanuse‘class’,areservedkeyword,followedbytheclassnameandacolon.Byconvention,allclassesstartinuppercase.Forexample:

classStudents:

pass

Tocreateaclassthattakesanobject:

classStudents(object)

The__init__()method

Immediately after creating an instance of the class, you have to call the __init__()function.Thisfunctioninitializestheobjectsitcreates.Ittakesatleasttheargument‘self’,aPythonconvention,whichgivesidentitytotheobjectbeingcreated.

Examples:

classStudents:

def__init__(self):

classEmployees(object):

def__init__(self,name,rate,hours):

Afunctionusedinaclassiscalledamethod.Hence,the__init__()functionisamethodwhenitisusedtoinitializeclasses.

InstanceVariables

When you add more arguments to the def_init_() besides the self, you’ll need to addinstance variables so that any instance object of the class will be associated with theinstanceyoucreate.

Forexample:



name.self=name

rate.self=rate

hours.self=hours

Intheaboveexample,name.self,rate.self,andhours.selfaretheinstancevariables.

WhenyoucreateinstancesoftheclassEmployees,eachmemberwillhaveaccesstothevariableswhichwereinitializedthroughthe__init__method.Toillustrate,youcancreateor‘instantiate’newmembersoftheclassEmployees:

staff=Employees(“Wayne”,20,8)

supervisor=Employees(“Dwight”,35,8)

manager=Employees(“Melinda”,100,8)

YoucanthenusetheprintcommandtoseehowtheinstancevariablesinteractedwiththemembersoftheclassEmployees:

print(staff.name,staff.rate,staff.hours)

print(supervisor.name,supervisor.rate,supervisor.hours)

print(manager.name,manager.rate,manager.hours)

ThePythonShellwilldisplaythisoutput:

Wayne208

Dwight358

Melinda1008

Hereishowtheentirecodewaswrittenontheeditor/filewindow:

Filewindow:employees.py

Here’stheoutput:

Inheritance

InheritanceisaPythonprocessthatallowsoneclasstotakeonthemethodsandattributesof another. This feature allows users to create more complicated classes that inheritmethods or variables from their parent or base classes and makes programming moreefficient.

Thisisthesyntaxfordefiningaclassthatinheritsallvariablesandfunctionfromaparentclass:

classChildClass(ParentClass):

Toillustrate,youcancreateanewclass,Resigned, thatwill inheritfromtheEmployeesclassandtakeanadditionalvariable,status:



self.name=name

self.rate=rate

self.hours=hours

staff=Employees(“Wayne”,20,8)

supervisor=Employees(“Dwight”,35,8)

manager=Employees(“Melinda”,100,8)

print(staff.name,staff.rate,staff.hours)

print(supervisor.name,supervisor.rate,supervisor.hours)

print(manager.name,manager.rate,manager.hours)

classResigned(Employees):

def__init__(self,name,rate,hours,status):

self.name=name

self.rate=rate

self.hours=hours

self.status=status

exemp_1=Resigned(“Dorothy”,32,8,“retired”)

exemp_2=Resigned(“Malcolm”,48,8,“resigned”)

print(exemp_1.name,exemp_1.rate,exemp_1.hours,exemp_1.status)

print(exemp_2.name,exemp_2.rate,exemp_2.hours,exemp_2.status)

HereistheoutputonthePythonShellwhenthecodeisexecuted;

Conclusion

Congratulationsforfinishingthisbook,IhopeitwasabletoequipyouwiththeessentialskillsandfundamentalknowledgetoexploreandharnessthepowerfulfeaturesofPythonasaprogramming language.By the timeyou finished reading thebook, I amconfidentthatyouwillbepreparedtoputyourbasicprogrammingknowledgetopracticaleverydayuses.

The next step is to take up advanced Python programming courses that will help youcreatemorecomplexprogramssuchasgames,webapplications,andproductivitytools.

Finally, ifyouenjoyedthisbook,pleasetakethetimetoshareyourthoughtsandpostapositivereviewonAmazon.It’dbegreatlyappreciated!

Thankyouandgoodluck!

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