Here is the error if I remove .toString() : 
```
arguments did not match any overloaded call:
  QgsVectorFileWriter(QString, QString, QgsFields, QGis.WkbType, QgsCoordinateReferenceSystem, QString driverName="ESRI Shapefile", QStringList datasourceOptions=QStringList(), QStringList layerOptions=QStringList(), QString newFilename=None): argument 2 has unexpected type 'QVariant'
  QgsVectorFileWriter(QgsVectorFileWriter): argument 1 has unexpected type 'unicode'
```
Do the script outputs/OutputVector.py has to `import qgis` ?