为开发人员准备的文档,涵盖QGIS的多种功能实现和代码。

CHAPTER1Introduction

Thisdocumentisintendedtoworkbothasatutorialandareferenceguide.Whileitdoesnotlistallpossibleuse

cases,itshouldgiveagoodoverviewoftheprincipalfunctionality.

Startingfrom0.9release,QGIShasoptionalscriptingsupportusingPythonlanguage.We’vedecidedforPython

asit’soneofthemostfavouritelanguagesforscripting.PyQGISbindingsdependonSIPandPyQt4.Thereason

forusingSIPinsteadofmorewidelyusedSWIGisthatthewholeQGIScodedependsonQtlibraries.Python

bindingsforQt(PyQt)aredonealsousingSIPandthisallowsseamlessintegrationofPyQGISwithPyQt.

TODO:GettingPyQGIStowork(Manualcompilation,Troubleshooting)

ThereareseveralwayshowtouseQGISpythonbindings,theyarecoveredindetailinthefollowingsections:

automaticallyrunPythoncodewhenQGISstarts

issuecommandsinPythonconsolewithinQGIS

createandusepluginsinPython

createcustomapplicationsbasedonQGISAPI

ThereisacompleteQGISAPIreferencethatdocumentstheclassesfromtheQGISlibraries.PythonicQGISAPI

isnearlyidenticaltotheAPIinC++.

TherearesomeresourcesaboutprogrammingwithPyQGISonQGISblog.SeeQGIStutorialportedtoPythonfor

someexamplesofsimple3rdpartyapps.Agoodresourcewhendealingwithpluginsistodownloadsomeplugins

frompluginrepositoryandexaminetheircode.Also,thepython/plugins/folderinyourQGISinstallation

containssomepluginthatyoucanusetolearnhowtodevelopsuchpluginandhowtoperformsomeofthemost

commontasks

1.1RunPythoncodewhenQGISstarts

TherearetwodistinctmethodstorunPythoncodeeverytimeQGISstarts.

1.1.1PYQGIS_STARTUPenvironmentvariable

YoucanrunPythoncodejustbeforeQGISinitializationcompletesbysettingthePYQGIS_STARTUPenviron-

mentvariabletothepathofanexistingPython le.

Thismethodissomethingyouwillprobablyrarelyneed,butworthmentioningherebecauseitisoneoftheseveral

waystorunPythoncodewithinQGISandbecausethiscodewillrunbeforeQGISinitializationiscomplete.This

methodisveryusefulforcleaningsys.path,whichmayhaveundesireablepaths,orforisolating/loadingtheinitial

environwithoutrequiringavirtenv,e.g.homebreworMacPortsinstallsonMac.