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ProDjangoMartyAlchinProDjangoCopyright2009byMartyAlchinAllrightsreserved.
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ISBN-13(pbk):978-1-4302-1047-4ISBN-13(electronic):978-1-4302-1048-1PrintedandboundintheUnitedStatesofAmerica987654321Trademarkednamesmayappearinthisbook.
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iiiContentsataGlanceAbouttheAuthor.
xiiiAcknowledgmentsxvPreface.
xviiIntroductionxixCHAPTER1UnderstandingDjango.
1CHAPTER2DjangoIsPython13CHAPTER3Models45CHAPTER4URLsandViews.
91CHAPTER5Forms113CHAPTER6Templates133CHAPTER7HandlingHTTP163CHAPTER8BackendProtocols183CHAPTER9CommonTools.
213CHAPTER10CoordinatingApplications231CHAPTER11EnhancingApplications.
253APPENDIXContributingtoDjango.
279INDEX285vContentsAbouttheAuthor.
xiiiAcknowledgmentsxvPreface.
xviiIntroductionxixCHAPTER1UnderstandingDjango1Philosophy.
1Django'sInterpretationoftheMVCPattern.
2LooseCoupling.
5Don'tRepeatYourself(DRY)5AFocusonReadability6FailingLoudly6Community8ManagementoftheFramework9NewsandResources.
10ReusableApplications.
10GettingHelp11NowWhat12CHAPTER2DjangoIsPython13HowPythonBuildsClasses13BuildingaClassProgrammatically14MetaclassesChangeItUp15UsingaBaseClasswithaMetaclass.
16DeclarativeSyntax.
17CommonDuck-TypingProtocols19Callables20Dictionaries.
21Files22Iterables.
23Sequences.
25NCONTENTSviAugmentingFunctions25ExcessArguments26Decorators.
28Descriptors34__get__(self,instance,owner)35__set__(self,instance,value)35KeepingTrackofInstanceData.
36Introspection.
36CommonClassandFunctionAttributes.
37IdentifyingObjectTypes37FunctionSignatures.
39Docstrings40AppliedTechniques.
41TrackingSubclasses41ASimplePluginArchitecture42NowWhat44CHAPTER3Models45HowDjangoProcessesModelClasses46SettingAttributesonModels46GettingInformationAboutModels47ClassInformation.
47FieldDefinitions48PrimaryKeyFields.
49ConfigurationOptions50AccessingtheModelCache.
52UsingModelFields57CommonFieldAttributes57CommonFieldMethods60SubclassingFields.
62DecidingWhethertoInventorExtend62PerformingActionsDuringModelRegistration.
63AlteringDataBehavior.
64ControllingDatabaseBehavior.
68DealingwithFiles71get_directory_name(self)71get_filename(self,filename)72generate_filename(self,instance,filename)72NCONTENTSviisave_form_data(self,instance,data)73delete_file(self,instance,sender)73attr_class.
74CustomizingtheFileClass74Signals.
76class_prepared.
77pre_initandpost_init78pre_saveandpost_save.
79pre_deleteandpost_delete80post_syncdb80AppliedTechniques.
82LoadingAttributesonDemand82CreatingModelsDynamicallyatRuntime87NowWhat90CHAPTER4URLsandViews91URLs.
91StandardURLConfiguration.
92ResolvingURLstoViews.
94ResolvingViewstoURLs.
95Views97TemplatesBreakItUpaBit98AnatomyofaView.
98WritingViewstoBeGeneric.
99ViewDecorators.
101UsinganObjectAsaView107AppliedTechniques.
109Dual-FormatDecorator109NowWhat111CHAPTER5Forms113DeclaringandIdentifyingFields113BindingtoUserInput.
114ValidatingInput.
115CustomFields.
117Validation.
117ControllingWidgets118NCONTENTSviiiDefiningHTMLBehavior.
119CustomWidgets.
119CustomizingFormMarkup.
123AccessingIndividualFields124CustomizingtheDisplayofErrors.
124AppliedTechniques.
125PendingandResumingForms.
125NowWhat132CHAPTER6Templates133WhatMakesaTemplate.
133Exceptions.
134TheProcessatLarge.
135ContentTokens135ParsingTokensintoNodes.
136TemplateNodes137RenderingTemplates138Context138SimpleVariableResolution.
139ComplexVariableLookup.
140IncludingAspectsoftheRequest141RetrievingTemplates141django.
template.
loader.
get_template(template_name)141django.
template.
loader.
select_template(template_name_list).
.
.
142ShortcutstoLoadandRenderTemplates142AddingFeaturesforTemplates.
143SettingUpthePackage.
143VariableFilters144TemplateTags146AddingFeaturestoAllTemplates148AppliedTechniques.
148EmbeddingAnotherTemplateEngine148EnablingUser-SubmittedThemes152NowWhat162CHAPTER7HandlingHTTP.
163RequestsandResponses.
163HttpRequest163HttpResponse169NCONTENTSixWritingHTTPMiddleware.
174MiddlewareClass.
process_request(self,request)174MiddlewareClass.
process_view(self,request,view,args,kwargs)174MiddlewareClass.
process_response(self,request,response)175MiddlewareClass.
process_exception(self,request,exception).
.
.
175DecidingBetweenMiddlewareandViewDecorators176HTTP-RelatedSignals178django.
core.
signals.
request_started178django.
core.
signals.
request_finished.
178django.
core.
signals.
got_request_exception178AppliedTechniques.
178SigningandValidatingCookies179NowWhat181CHAPTER8BackendProtocols183DatabaseAccess183django.
db.
backends184CreationofNewStructures189IntrospectionofExistingStructures191DatabaseClient192DatabaseErrorandIntegrityError.
193Authentication193get_user(user_id)193authenticate(**credentials)193StoringUserInformation.
194Files194TheBaseFileClass194HandlingUploads.
196StoringFiles198SessionManagement199Caching201SpecifyingaBackend201UsingtheCacheManually202TemplateLoading203load_template_source(template_name,template_dirs=None)203load_template_source.
is_usable204ContextProcessors204NCONTENTSxAppliedTechniques.
205LoadingTemplatesUsingaDifferentEngine205ScanningIncomingFilesforViruses.
210NowWhat212CHAPTER9CommonTools213CoreExceptions213django.
core.
exceptions.
ImproperlyConfigured213django.
core.
exceptions.
MiddlewareNotUsed214django.
core.
exceptions.
MultipleObjectsReturned214django.
core.
exceptions.
ObjectDoesNotExist.
215django.
core.
exceptions.
PermissionDenied215django.
core.
exceptions.
SuspiciousOperation216django.
core.
exceptions.
ViewDoesNotExist216TextModification217get_text_list(items,last_word='or'217javascript_quote(s,quote_double_quotes=False)217normalize_newlines(text)217phone2numeric(phone)218recapitalize(text)218smart_split(text)218truncate_words(s,num)219truncate_html_words(s,num)219wrap(text,width)219DataStructures220django.
utils.
datastructures.
MergeDict220django.
utils.
datastructures.
MultiValueDict221django.
utils.
datastructures.
SortedDict.
222FunctionalUtilities222django.
utils.
functional.
curry.
222django.
utils.
functional.
memoize223django.
utils.
functional.
wraps.
225Signals.
226HowItWorks.
226DefiningaSignal226SendingaSignal227CapturingReturnValues.
227DefiningaListener.
227NCONTENTSxiRegisteringListeners.
228ForcingStrongReferences.
228NowWhat229CHAPTER10CoordinatingApplications.
231Contacts231contacts.
models.
Contact232contacts.
forms.
UserEditorForm.
233contacts.
forms.
ContactEditorForm234contacts.
views.
edit_contact.
235AdminConfiguration238URLConfiguration238RealEstateProperties.
241properties.
models.
Property241properties.
models.
Feature246properties.
models.
PropertyFeature.
246properties.
models.
InterestedParty246AdminConfiguration247URLConfiguration251NowWhat252CHAPTER11EnhancingApplications253RecordingtheCurrentUser253TheThread-LocalApproach—UsefulbutDangerous254TheAdminApproach.
256IntroducingtheCurrentUserField.
257KeepingTrackofCurrentUserFieldInstances.
257TheCurrentUserMiddleware259PerformanceConsiderations261KeepingHistoricalRecords263IntendedUsage.
264OverviewoftheProcess266Step1:CopytheModel.
267Step2:RegisterSignalHandlers.
272Step3:AssignaManager272NowWhat278NCONTENTSxiiAPPENDIXContributingtoDjango.
279ReportingaTicket279SupplyingaPatch279WritingTests.
280WritingDocumentation.
280DevelopmentSprints.
281PublishingCode281ReleasinganApplication282INDEX285xiiiAbouttheAuthorNMARTYALCHINisaprofessionalprogrammerwithapassionfortheWeb.
Overthepasttwoandahalfyears,hehasdevelopedandreleasedafewDjangoapplicationsandasignificantimprovementtoDjango'sfilestoragehandling.
Raisedinthewildbyapackofmechanicalengineers,Martylearnedatayoungagetheimportanceofknowinghowthingsworkandhowtoimprovethem.
Whennotcodingforwork,hegoesbythenameGulopineandcodesforfun.
Hekeepsablogatdppl6++i]npu]h_dej*_ki+,wheremuchofthiscodeisannouncedanddescribed.
xvAcknowledgmentsIcan'timagineanyonetakingonaprojectlikethisalone.
IntheyearandahalfsinceIfirstconsideredputtingmythoughtsonpaper,noonehasbeenmoresupportivethanmybeauti-fulwife,Angel.
Withouther,I'dbelostandconfused,mumblingincoherentlyaboutdeclarativemetaclassimplementations.
Therearenowordstoexpresshowmuchhelpshe'sbeenthrough-outtheprocess.
I'dalsoliketothankGeorgeVilchesforsteppinguptotakeonabookhehadn'tbeeninvolvedwithfromthebeginning.
He'sbeenanamazingasset,goingwellbeyondwhatwasrequiredofhimtomakesurethisbookisasgoodaswecouldpossiblymakeit.
Ofcourse,theLawrenceJournal-WorldanditsInternetdivisionaretothankfortheDjangoWebframework'sexistenceandforitsreleasetothepublic,whichmadeallofthispossibleinthefirstplace.
Idon'texpecttheyhadanyideahowfaritwouldgowhendesigningandreleas-ingit.
Ihaveafeelingthisisfarfromtheend.
Infact,theentirecommunitythatsurroundsDjangohasfueledmeinmorewaysthanIcanexplain.
It'sbecauseofpeoplelikeyouthatIchosetotakeonthischallenge,andit'sthethoughtofagreatercommunitythatkeepsmegoing.
Thankyou.
xviiPrefaceProgramminghasalwaysbeenequalpartsartandscience.
It'seasytoseethescienceinteachingcomputershowtodothings,butoncethat'soutoftheway,weoftentrytoembracetheartisticside.
Wespendourfirstfewyearslearningtomakecodefunctionalandtherestofourcareerstryingtomakeitbeautiful.
Djangostarteditslifeinmuchthesameway,servingtheday-to-dayneedsofalocalnewsorganization.
Intheyearssinceitsfirstpublicrelease,Djangoitselfhasgrownmoreelegantandhashelpeditsadopterstowritemoreelegantcodefortheirownapplications.
Thisfocusonbeautyisn'tuniquetoDjango.
MostPythonapplicationsstriveforanotionofbeing"Pythonic"—anunwrittenidealthatembodiesthenatureandspiritofthePythonlan-guageitself.
Havingavaguegoallikethatmayseemproblematic;afterall,howdoyouknowwhenyou'vesucceededIronically,that'sthepoint:thereisnofinishline.
There'snotevenameasuringsticktotellyouhowcloseyouaretoachievingyourgoal.
Thetruegoalisthejourneyitself,thelessonslearnedalongtheway,thediscoveriesthatopenyoureyestonewideas.
Pythonincludesanumberoftoolsthatmakethisprocessquiteinteresting,especiallyforthoseprogrammerscomingfromotherlanguages.
Djangobuildsonthattoolset,addingitsowntechniquesforeasingtheburdenonotherprogrammers,makingiteasytoproducemorebeautifulcodeallaround.
IfirstgotstartedwithDjangoshortlyafteritcompletedits"magicremoval"phase,whichwasalongprocessofmakingtheframeworkmorePythonicoverall.
IwasnewtoPythonatthetime,andreadingabouttheprocessandtheidealsthatencourageditcausedmetodigdeeperintowhatmadeDjangowork.
Iwasfascinatedbytherichnessofthetoolsetatmydisposalandquicklybeganmyownjourneyofdiscovery.
WhatfascinatedmemostwashowfewpeopleknewaboutsomeofthetricksthatcanbeusedtoencouragePythoniccodeforprogrammersusingtheframework.
EverytimeIshowedanewtricktosomeone,IjokedthatIcouldwriteabookaboutwhatI'velearnedsofar.
Afterseveralmonthsofdoingso—andseveralpeopleencouragingmetodropthejokeanddoitforreal—IfinallytooktheplungeandcontactedApress.
I'mnotinterestedinmakingafortunewiththisbook.
MygoalhasalwaysbeentohelpmorepeopleunderstandthemanytoolsavailablewithPythonandDjango,inhopesthattheytoocanhaveenrichingjourneysoftheirown.
IhopethisbookwillhelpbringDjangotonewpeopleandnewplaces,whereitmighthavebeenpreviouslyconsideredinappropriate.
ThoseofusworkingwithDjangoareoftencalledDjangonautswithgoodreason.
The"-naut"suffixhasbeenusedhistoricallytorepresentsailorsandisthesameconceptasintheword"nautical.
"Moregenerally,itoftenreferstothosewhosailintotheunknown,suchasastronautsandcosmonauts.
Itrepresentsexplorersandadventurers,thosepeoplebraveenoughtochallengewhattheyknewbeforeanddaretodiscovernewthingsandnewplaces.
IamaDjangonaut.
Whatfollowsismyjourneythusfar.
xixIntroductionProDjangorepresentstwoandahalfyearsofaccumulatedknowledgeinPythonandDjango,designedtoeducatereaderswhoarealreadyfamiliarwithbothtopicsandwouldliketotakethemfurtherthantheyhadpreviouslydone.
Youwilllearnawiderangeofadvancedtech-niquesavailableinbothPythonandDjango,alongwithtipsonhowtousethemtoachieveadvancedfunctionality.
Thisbookisdesignedtobebothanarrativetobereadfromstarttofinishandageneralreferencetobesearchedforspecificinformation.
Sinceyoumaynotknowwhattolookfororwheretofindityet,feelfreetoreadthroughthebookfirst,thenkeepithandyforrefreshingyourmemoryasnecessary.
WhatThisBookIsNotThereareplentyofresourcesavailableforlearningPythonandDjango,sothisbookdoesnotstrivetoteachthebasics.
ForreadersnewtoPython,IhighlyrecommendDiveIntoPythonbyMarkPilgrim(Apress,2004).
ForlearningDjango,I'drecommendTheDefinitiveGuidetoDjango:WebDevelopmentDoneRightbyAdrianHolovatyandJacobKaplan-Moss(Apress,2006).
Additionally,PracticalDjangoProjectsbyJamesBennett(Apress,2008)isanexcellentresourceforgeneralapplicationdevelopment.
WhoThisBookIsForBecauseProDjangodoesn'tdwellonintroductorydetails,readerswillbeexpectedtohaveexperiencewithbothPythonandDjango.
Ifyou'renewtoeithersubject,pleaseconsideroneofthebooksmentionedintheprevioussectionbeforetryingtotacklethisbook.
Evenifyou'veonlyexperimentedonyourownwithoutlaunchingafullsiteyet,abasicfamiliarityshouldbesufficient.
Youdon'tneedtobeanexperttostartreadingProDjango,butyoumightbebythetimeyoufinish.
InterpretingCodeSamplesProDjangousesasimpleformat,interleavingexplanationsofPython'sandDjango'savailablefeatureswithcodethatdemonstratestheiruseintherealworld.
Therearetwotypesofcodesamplesused,whichdifferinhowtheyshouldbeexecuted.
Python'sinteractiveinterpreterisagreatwaytotestoutsmallpiecesofcodeandseehowitworksinavarietyofsituations.
Linesofcodeintendedforuseinthatenvironmentwillalwaysbeprefixedwiththreecharacters:threegreater-thansigns(:::)orthreeperiods(***).
Lineswithgreater-thansignsaretheoutermostblockofcode,whiletheperiod-prefixedlinesareindentedatleastonelevel.
Thethreeinitialcharactersarealsofollowedbyaspace.
TheseNINTRODUCTIONxxfirstfourcharactersarenottypedintotheinteractiveinterpreterdirectly;theysimplymimicwhattheinterpreteritselflookslikebyreproducingitsoutput.
AlinestartedwiththreeperiodsbutcontainingnoothertextindicatesthatyoushouldsimplypressEnteronablanklineintheinterpreter.
Thiscompletesanyopencodeblocks,bringingyoubacktothe:::prompt.
Anylinesthatdon'tbeginwitheither:::or***repre-senttheoutputofthecodeortheresultofthepreviousexpression.
:::eilknp`f]jck:::lnejp`f]jck*cap[ranoekj$%q#-*,)bej]h#Thefirstlineofaninteractiveexamplewillalwaysbeginwith:::;everythingelseiscodethatshouldbewritteninafileandexecutedaspartofarunningDjangoapplication.
Thesur-roundingtextwillindicatewhatfilethecodeshouldbeplacedinandhowitwillexecute.
PrerequisitesProDjangoiswrittenforDjango1.
0,whichwasreleasedonSeptember3,2008.
ThatreleaseoramorerecentcheckoutfromtheDjangocoderepositoryisrequiredforthecodesamplestoworkproperly.
SinceDjangointurnreliesonPython,theseexamplesalsoassumeaworkingPythonenvironmentofversion2.
3orhigher.