Handbook of the Physics Computing Course

43 Pages·0.18 MB·English

by  Williams M.

Handbook of the Physics Computing
Course
Michael Williams
December3, 2002

Copyright(cid:0)c 2002MichaelWilliams;thisdocumentmaybecopied,distributedand/ormodifiedundercertaincondi-
tions,butitcomesWITHOUTANYWARRANTY;seetheDesignScienceLicenseformoredetails.
Acopyofthelicenseis:
(cid:1) includedintheLATEXdistributionofthisdocument—seehttp://users.ox.ac.uk/sann1276/python.
(cid:1) alwaysavailableathttp://dsl.org/copyleft/dsl.txt.
ii
CONTENTS
1 Introduction 1
1.1 ThePythontrial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Typographicalconventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 Usingthesystem 3
2.1 Loggingin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2 IDLEbasics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.3 ProgrammingusingIDLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.4 Casesensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3 TheelementsofPython 7
3.1 Helloworld . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2 Interpreters,modules,andamoreinterestingprogram . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3 Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.4 Inputandoutput . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.5 Arithmetic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.6 forloops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.7 ifstatements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.8 whileloops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.9 Usinglibraryfunctions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.10 Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.11 Makingyourownfunctions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.12 Fileinputandoutput . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.13 Puttingitalltogether . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4 GraphicaloutputandadditionalPython 27
4.1 Graphicaloutput . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.2 ArraysinPython . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.3 Functionsyoumayneedforthefirst-yearproblems . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.4 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.5 Pythondifferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.6 Takingyourinterestfurther . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
A Errors 35
A.1 AttributeErrors,KeyErrors,IndexErrors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
A.2 NameErrors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
A.3 SyntaxErrors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
A.4 TypeErrors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
B ReservedWords 37
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CHAPTER
ONE
Introduction
1.1 The Python trial
Thankyouforparticipatinginthistrialofaproposednewfirstyearcomputingcourse. Duringthistrialwewouldlike
youtoconsultdemonstratorsasmuchasyoulike. Itisbeingrunforustoironouttheproblemsinthecourse,andso
wewillbemostappreciativeofanyfeedbackthatyoucangiveusaboutthecourseorthehandbook. Ofcourse,we
alsohopeyouwillfindthetrialinterestinganduseful!
LikethePascalcourseyoudidlastyearthistrialconsistsofthefollowingelements:
Usingthesystem Logging in; using the graphical interface; files; using the Python interpreter; creating, editing,
storingandrunningprograms. YouwilllearnsomeoftheskillsassociatedwiththeuseoftheUNIXoperating
system.
TheelementsofPython Learning enough of a programming language to write simple but useful programs, while
beingintroducedtotheconceptsofproceduralprogramming.
TointroduceyourselftothebasicsofPythonyouwillneedtoreadthroughChapter3,“TheelementsofPython”
anddotheexercisesgivenasyougoalong. Ifyoudonotunderstandhowtotackleaparticularexerciseplease
consultademonstrator.
Thehandbookshouldcontainalltheinformationyouneedtocompletetheexercisesandtheproblemyouwill
bedoing.
ProgrammingProblems Once you have gone through the introduction to Python we would like you to attempt a
more substantialproblem. Youmay selectonefrom the followinglist (youmay selectthe oneyou did in the
firstyearifyouwish):
CO11 QuadraticEquation;straightlinefittingbyleastsquares
CO12 NucleardecayandtheDopplereffect
CO13 NumericalIntegrationbySimpson’sruleandbyaMonteCarlomethod
CO14 Solutionofnon-linearequations;solutionofadifferentialequation
CO15 Polynomialcurvefittingbyleastsquares
CO16 Graphplotting;FourierAnalysis
Note: whicheverproblemyouchoose,forthepurposesofthetrialitwillberecordedasexperimentCO91
Whilst it is not required, we would like you to use your logbooks to make notes as you do the course; in anycase,
you will not need to produce a write-up of the problem you attempt. Rather, we will ask you to discuss it with a
demonstratorandfillinaquestionnaire.
This course deliberately covers only a subset of Python, which is an extremely powerful and flexible language. In
doing the course you should acquire skills applicable both to Python and to programming in general. Python has
1
beenchosenbecauseitispossibletoteachenoughofthelanguagetowriteusefulprogramsrelativelyquickly,yetit
is potentially a very powerful language, which is being increasingly used throughout academia and the commercial
softwareindustry.
1.2 Typographical conventions
Thishandbookusesthefollowingtypographicalconventions:
MostofthedocumentappearsintheTimesfont.
Typewriter fontisusedforanythingtyped,e.g. PythoncodeorUNIXcommands.
Sansserifisusedformenuandapplicationnames
Newtermsandotherpiecesofjargonarewritteninitalicsthefirsttimetheyareused. [Thesewillbedescribedina
glossaryinalateredition].
2 Chapter1. Introduction
CHAPTER
TWO
Using the system
2.1 Logging in
SitatoneoftheSunterminals. Movethemouse: thescreenshouldcomeon;ifitdoesn’tafterafewseconds,press
thepowerbuttoninthebottom-rightcornerofthemonitor,sothegreenLEDislit.
You should see a login panel: using lower case, enter your usual Physics username where indicated and then press
Returnbutbeforeyouenteryourpassword, ensurethatthegraphicontherightsays“SolarisCommonDesktop
Environment”. If itdoes not, thenclick andhold the Optionsbutton, andselectCommon Desktop Environment
fromtheSessionmenu. NowenteryourpasswordandpressReturn.
Theloginpanelshoulddisappearandafterafewseconds, youshouldseevariouswindowsappearonthescreen. If
youwanttobeabletousetheNetscapewebbrowser—whichwerecommend—clickAcceptinitsLicensepanel(a
Netscapebrowserwindowwillthenappear,whichyoucanminimisebyclickingonthe“dot”buttonatthetop-right
ofitswindow). Youshouldalso mimimisetheHelp Viewer andFile Managerwindowsinthesame manner. You
shouldnowbeleftwithasingleTerminalwindow.
IfyoudonotseeaTerminalwindow,thenyoucangetanewoneatanytimebyclickingonceontheterminaliconat
thebottom-rightofthescreen(itshouldbethethirdiconfromtheright). ClickintheTerminalwindowsoitsborder
turnsdarkpink(thisindicatesthatyoucantypethingsintoit).TerminalsprovideaccesstowhatisknownastheUNIX
command-line,orshell. AUnixshellisabitliketheDOS-promptinMicrosoftWindows,butitisfarmorepowerful
andflexible: itmakesavailablehundredsofcommands,utilitiesandprograms. Theshellindicatesthatitisreadyto
receivecommandsbydisplayingthefollowing1prompt:
rayleigh%
SomebasichelpandinformationaboutUnixcommandsisavailablebytypinghelpinaTerminalwindow. Mostly,
however,youwillnotneedtousetheshellbecausewehavemadeavailableasingle,integratedapplicationfordoing
PythonprogrammingcalledIDLE.
2.2 IDLE basics
ThissectiondescribestheIDLEapplicationthatyouwillbeusingwhenyoustartwritingyourownPythonprograms
inthenextchapter.YouwillprobablyneedtoreferbacktoitwhenyoustartworkingthroughChapter3.
IDLEisPython’sIntegratedDeveLopmentEnvironment;inotherwordsitisanapplicationwhichenablesyoutoboth
writeandrunPythonprograms. 2
TostartupIDLEtypeidleattheshellpromptandpresstheReturnkey:
1Thisisthedefaultshellprompt:itcanbecustomized.
2IfyouarefamiliarwithUNIXorLinuxyoumayalternativelyuseyourfavouriteUNIXtext-editortowriteyourPythonprograms,andthenrun
themyourselfusingthepythoncommand.However,IDLEdoesprovideaniceenvironmentfordevelopingPythoncode,sowerecommendyou
tryusingit.
3
rayleigh% idle
Note: idleistypedentirelyinlowercase—seeSection2.4,“Casesensitivity”.
Atthispoint,youmaywishtominimisetheTerminalwindow;doNOTcloseitorIDLEwillbekilled!
AfterafewsecondsanewwindowcalledPythonShellwillappear.ThisisIDLE’sinterfacetothePythoninterpreter.
Aninterpreterisaprogramwhichtranslatestheprogramsourcecodeyouenterintomachinecodewhichthecomputer
canunderstandandrun. Chapter3explainsallaboutusingthePythoninterpreter.
IDLE also includes an editor which is an application, rather like a simple word-processor, that you use to write
programs(or indeed anykind oftext). IDLE’s editor has been customizedto makeit particularlyusefulfor writing
Python programs, and it should be fairly intuitive to use. Documents are opened, closed and saved by selecting
commandsintheFilemenu.
2.2.1 Creating a new program
SelectingNewWindowfromtheFilemenuwillopenanemptyeditorwindowcalledUntitled.
2.2.2 Opening existing programs
YoucanretrieveapreviouslysavedprogrambychoosingOpenfromtheFilemenuandselectingthefiletoopen.
2.2.3 Saving programs
After typing or editing a Python program, save the file by selecting Save from the File menu. The first time you
saveafile,SavewillactuallybehavelikeSaveAs;inotherwords,asmallwindowwillappearwhereyoucanenter
thenameyouwishtogiveyourprogram. Onsubsequentoccasions,Savewillsimplysavethefile. Oncesaved,the
programremainson-screenforfurthereditingifyouwish.
2.2.4 Closing programs
IfyoureallyhavefinishededitingyourprogramthenchooseClosefromtheFilemenu. Ifthereareunsavedchanges
youwillbepromptedtosavethem.
In general, when you have finished with a window you should close it rather than minimising it as otherwise your
screenwillbecomeclutteredwithlotsofminimisedwindowicons.
2.3 Programming using IDLE
As you will see in Section 3.2 it is possible to write programs either interactively or by using the editor. You will
probablyneedtoreferbacktothissectionwhenyoustartwritingyourownprograms.
2.3.1 Using the interactive interpreter
ManyoftheexamplesinthishandbookusePython’sinteractiveinterpreter. Ifyoudon’talreadyhaveoneopen,you
cangetaninteractivewindow(aPythonShell)byselectingPythonShellfromtheRunmenu.
4 Chapter2. Usingthesystem