Within your IDE settings, point it to use the Python interpreter included withOSGeo4W---typically at: %OSGEO4W_ROOT%\bin\python3.exe. This will make it pick upall the QGIS goodies needed for development, completion, and debugging. In mycase OSGEO4W_ROOT is C:\OSGeo4W3, so in the IDE, the path to the correctPython interpreter would be: C:\OSGeo4W3\bin\python3.exe.