QGIS-2.8-PyQGISDeveloperCookbook-en(6)

为开发人员准备的文档,涵盖QGIS的多种功能实现和代码。

1.1.2Thestartup.py le

EverytimeQGISstarts,theuser’sPythonhomedirectory(usually:.qgis2/python)issearchedfora le

namedstartup.py,ifthat leexists,itisexecutedbytheembeddedPythoninterpreter.

1.2PythonConsole

Forscripting,itispossibletotakeadvantageofintegratedPythonconsole.Itcanbeopenedfrommenu:Plugins

→PythonConsole.Theconsoleopensasanon-modalutility

window:

Figure1.1:QGISPythonconsole

Thescreenshotaboveillustrateshowtogetthelayercurrentlyselectedinthelayerlist,showitsIDandoptionally,

ifitisavectorlayer,showthefeaturecount.ForinteractionwithQGISenvironment,thereisaifacevariable,

whichisaninstanceofQgsInterface.Thisinterfaceallowsaccesstothemapcanvas,menus,toolbarsand

otherpartsoftheQGISapplication.

Forconvenienceoftheuser,thefollowingstatementsareexecutedwhentheconsoleisstarted(infutureitwillbe

possibletosetfurtherinitialcommands)

Forthosewhichusetheconsoleoften,itmaybeusefultosetashortcutfortriggeringtheconsole(withinmenu

Settings→Con gureshortcuts...)

1.3PythonPlugins

QGISallowsenhancementofitsfunctionalityusingplugins.ThiswasoriginallypossibleonlywithC++language.

WiththeadditionofPythonsupporttoQGIS,itisalsopossibletousepluginswritteninPython.Themain

advantageoverC++pluginsisitssimplicityofdistribution(nocompilingforeachplatformneeded)andeasier

development.

ManypluginscoveringvariousfunctionalityhavebeenwrittensincetheintroductionofPythonsupport.Theplu-

gininstallerallowsuserstoeasilyfetch,upgradeandremovePythonplugins.SeethePythonPluginRepositories

pageforvarioussourcesofplugins.

CreatingpluginsinPythonissimple,seeDevelopingPythonPluginsfordetailedinstructions.