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CPSC301:ComputingintheLifeSciences
LectureNotes7:
PythonModules&Testing
pre-classnotes
JessicaDawson
[email protected]
http://www.cs.ubc.ca/~jqdawson
UniversityofBritishColumbia
DepartmentofComputerScience
2016W2
OriginalslidesbyIanM.MitchellandGeorgeTsiknis.Revisions/updatesbyJessicaDawson
Objectives
Attheendofthissection,youwillbeableto:
• Useimport andrelatedcommandstoaccessvariables,
functionsandobjects(andlatermethodsandclasses)from
otherfiles
• Writeyourownmodules(actually,youhavebeendoingthis
allalong)
• Usethedoctest moduletoautomaticallyrunthetest
examplesindocstrings
• Designyourownmoduleswhichwillautomaticallytest
themselveswhentheyarerunbutnotwhentheyare
imported
Notes7:Modules
2
PythonModules
•
•
Amoduleisacollectionof(usuallyrelated)functionsanddata(variables)
groupedinasinglefilewith.py extension.Thefilename,(withoutthe".py"),
isthenameofthemodule
Pythoncomeswithhundredsofmodules
– math modulehasmanyfunctionslike
• sqrt
• etc.
•
•
•
•
(squareroot),trunc (trancate afloattoint),sin
Tousethefunctionsofamodulewehavetoimportitwiththestatement
import module-name,or
import module-nameas local-name
Afterimportingamodule,Pythoncreatesavariablewiththemodulename
(originalorlocal,ifdefined)whichreferencesthatmodule.
Tocallafunctioninthatmoduleyouhavetousemodule-name.functionnameasthefunctionname
Example:
import math
var = 2.95
math.tranc(var)
Notes7:Modules
3
PythonModules(cont)
• Amodulemayalsohaveasetofdata
– i.e.themathmodulehas
e=2.7182818284590451
pi=3.1415926535897931
theseareconstantvaluesthatyoucanuse,butmustnotchange:
radius=4.0
circle_area =math.pi *radius**2
• Youcanimportonlywhatyouwantfromamoduleusing:
frommathimportfloor,pi
circle_area =floor(pi*radius**2)
noneedtouse
math.pi or
math.floor
• Butifyoulaterimportanotherfunctioncalledfloor()fromanother
moduleonlythelastonewillbeavailable.
• Allbuilt-infunctionsareinthemodule__builtins__ .Thismodule
isautomaticallyimported
• Tocheckthecontentofamoduleyoucanuse:
help(module) - longcomments
dir(module) - onlynamesofitems
Notes7:Modules
4
DefiningModules
• EveryPythonfile(withextension.py)isamodule
– everytimeyoucreateaprogramandsaveit,youcreatea
module
– youcanimportandusethismoduleinanotherprogram
• Example:
– populationgrowthfunctionisinfilepgrowth.py
– touseit,theprogrambirthratehastoimportit
• HowdoesPythonfindsthefilesthatneedstoimport?
– Pythonfirstlooksinthedirectoriesthatcontainitslibraries,
calleddefaultdirectories
– thenitlooksinthecurrentdirectory
– inSpyder thecurrentdirectoryisthedirectorythatcontainsthe
lastprogramthatwasexecuted
– fornow,wecanimportanyfilesfromthedefaultorcurrent
directories,butnotfromanyotherdirectory(seelaterformore)
Notes7:Modules
5
ImportingModules
• Whenamoduleisimported,Pythonexecutesit.Wesaythatthe
moduleisloaded(inmemory).
• Whenamoduleisimportedagaininthesamesession,Pythondoes
notloaditagain.Itknowsthatitisalreadyin.
• Inmanycases,wewanttoexecutedifferentpartsofthemodule
whenitisimportedthanwhenwerunitasthemainprogram
• Pythondefinesavariable__name__ (twounderscoresbeforeand
after)withineachmodulethatissetautomatically
•
Byconvention,implicitPythonentities(entitiessuchasvariablesand
functionswhichPythoncreatesautomatically)aregivennamesthat
beginandendwithdoubleunderscore
• Whenamoduleisrunasthemainprogram(i.e.directlyinthe
consoleorbyclickingtherunbutton),its__name__ variableisset
to‘__main__’.Whenamoduleisimported,its__name__ variable
issettoitsname.
• Therefore,ifwewanttorunsomecodeonlywhenamoduleruns
asthemainprogramweincludethatcodeintheconditional:
if __name__ == '__main__':
• Typicaluse:Testsforthemodule.Wedon'twanttoexecutethem
whenthemoduleisimported.
Notes7:Modules
6
Amodulefoo
• Inthesubsequentclickerquestions,assumethatfoo.py
containsthefollowinglines:
def bar(x):
print('name in bar:', __name__)
return x * 2
def baz(x):
return x / 2
print('name is: ', __name__)
if __name__ == '__main__':
print('in main')
else:
print('not in main')
print('final line')
Notes7:Modules
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Testing
• Astheydevelopaunitofcode(likeafunction,amodule),
programmerstesttheunitbyperformingunittesting ontheunit
• Aunittestingconsistsofasetoftestcases forthatunit
• Atestcase consistsoftheinputvalues andtheexpectedoutput
• Apopularstyleofprogrammingisthetest-drivendevelopment
(TDD):
– writethetestcasesbeforeyouwritethecodefortheunit
• Whenallunitshavebeendevelopedandtested,wetestthewhole
programtoverifythatsatisfiestheuserrequirements
• Thetestingofthewholeprogramisusuallycalledsystemtesting
andtherearemanytypesofthat:
–
–
–
–
alphatesting :donebydevelopers
betatesting :donebysomeselectedusers
installationtesting :doneatthefinalsite
etc
Notes7:Modules
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Black-boxTesting
• Thetypeofunittestingthatweusuallyperforminatest
drivendevelopmentiscalledblack-boxtesting.
• Inablack-boxtesting,thetestcasesforaunitareusually
derivedfromtheunit'sspecificationandinclude:
– typicalcases whichusetypicalvaluesfortheinputs
– boundarycases thatuseboundaryvalues:valuesthatarethe
smallestorlargestallowablevaluesfortheunit'sinputs
– simplestinterestingcases whoseinputvaluesarecloseto
boundaryvalues
• Examplesofboundaryandinterestingcases:
– Fornumbers:zero,positiveandnegativetypicalvalues,largest
andsmallestallowedvalues,onevalueawayfromthesmallest
andlargestvalue
– Forcollections(likestrings,ranges,lists,etc):emptycollection,
collectionwithoneelement,collectionswithduplicatevalues
– Forsearching:nomatchfound,onematch,manymatches.
Notes7:Modules
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ExampleofTestCases
• Example:Thetestcasesforaunittestingofthepopulation
functioninthepgrowth module:
– typicalcase:
population(1000,20,10,10)shouldreturn2594
– boundarycase:
population(1000,0,0,anyperiods)shouldreturn1000
– boundarycase:
population(1000,0,10,1)shouldreturn900
– boundarycase:
population(1000,10,0,1)shouldreturn1100
– boundarycase:
population(1000,any,any,0)shouldreturn1000
– interestingcase:
population(1000,20,10,1)shouldreturn1100
• pgrowth_test.py containsthesetestcases
Notes7:Modules
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doctest :AsimplePythonLibraryforTesting
• Programmersuseavailablelibrariestohelpthemwriteand
maintaintheirtests
• doctest isaverysimplemodulefortestthatwecanwritewithin
thedocstring,exactlyliketheexamplesweuseinourrecipe
• doctest
– searchesthedocstringforlinesthatstartwith>>>
– executesthemand
– comparestheoutputwiththenextlinewhichsupposedtohavethe
expectedresult
• Comparisonisexactstringmatch(includinganyspaceornewline
characters)
• Toactivatethedoctest whenthemoduleisexecutedasmain
program,weneedtouse:
if __name__ == "__main__":
import doctest
doctest.testmod()
• Check pgrowth_doctest.py foranexample.
Notes7:Modules
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OtherPythonTestingFrameworks
• Therearemajorlimitationstothedoctest module
– Itisdifficulttocreatetestcaseswhichrequiresettingupany
significantamountofdata
– Testforsuccessisbasedonmatchingstrings
• Pythonalsohasunittest andnose modules
– Youcandefinemorecomplextestcases
– SuccesscanbedefinedintermsofanyBooleanexpression
• Theunittest moduleispartofthePythonstandardlibrary
– AnyinstallationofPythonwillincludethismodule
• Thenose modulebuildsontopofunittest
– Claimstobeeasiertobuild,runandmaintaintestsuites
– Alsosupportsextensivecollectionof“plug-ins”
Notes7:Modules
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Summary
• Afilewiththe.py extensioniscalleda“module”
• Amodulecancontainmanyrelatedvariables/functions/objects
• Pythonprovidesseveralwaysofexecutingthecommandsina
module:import andfrom ... import
• Thecommandsinamoduleareexecutedonlyonce,nomatterhow
manytimesitisimported
• Thenamesofthevariables/functions/objectsdefinedinthe
otherfiledependonhowitisimported
• Afilecandeterminewhetherithasbeenimportedorrundirectly
byexaminingthe__name__ variable
• Thedoctest modulecanbeusedtoautomaticallyrunthe
exampletestsinamodule’sdocstrings
• Pythonprovidesseveralotherframeworksforautomatingmore
complicatedtestprocesses
Notes7:Modules
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