Saving QgsVectorLayer to file using PyQGIS

Question

Isn't there a save method for QgsVectorLayer created for example like this:

i_out = processing.run("native:buffer", 
    {'INPUT':'C:/GIS/data/testdata/ak_riks.shp',
    'DISTANCE':100000,'SEGMENTS':5,'END_CAP_STYLE':0,
    'JOIN_STYLE':0,'MITER_LIMIT':2,'DISSOLVE':True,
    'OUTPUT':'TEMPORARY_OUTPUT'})['OUTPUT']

print(type(i_out))
<class 'qgis._core.QgsVectorLayer'>

The way I save it now is:

processing.run("gdal:convertformat",{
    'INPUT':i_out,
    'OPTIONS':'',
    'OUTPUT':'C:/GIS/data/testdata/fdsfdsds2.shp'
    })

Does not seem to be a save method:

for m in dir(i_out):
   if m.startswith("save"):
      print(m)

saveDefaultMetadata
saveDefaultStyle
saveNamedMetadata
saveNamedStyle
saveSldStyle
saveStyleToDatabase

Answer 1

QgsVectorLayer and QgsVectorDataProvider classes don't have any "save as"-like method. Therefore, you have to use writeAsVectorFormatV2 method of QgsVectorFileWriter class in version 3.10.3+ (or writeAsVectorFormat in earlier 3.x version ).

Using writeAsVectorFormatV2:

i_out = processing.run("native:buffer", {.....})["OUTPUT"]

path = "/Path/To/File.shp"    
options = QgsVectorFileWriter.SaveVectorOptions()
options.driverName = "ESRI Shapefile"

QgsVectorFileWriter.writeAsVectorFormatV2(i_out, path, QgsCoordinateTransformContext(), options)

Answer 2

I developed a plugin that saves the qgis project as .qgs and all vector layers as .gpkg while maintaining their original styles and formatting. Published it on the official plugin repo for all to use and modify as needed. Hope this helps! https://plugins.qgis.org/plugins/SaveAllScript/