Shapefile from selected features in PyQGIS

Question

I am trying to develop a plugin to export selected features from a layer as shapefile.

I have a comboBox from which I can select features. After selecting features in comboBox, I tried following code but unable to get new shapefile of these particular features.

Initially I defined a location for exported shapefile by using push button.

    def select_output_file(self):
         filename, _filter = QFileDialog.getSaveFileName(
                   self.dlg, "Select   output file ","", '*.shp')
         self.dlg.lineEdit.setText(filename)

And then connect to this function:-

    def run(self):
           if self.first_start == True:
              self.first_start = False
              self.dlg = GetMapDialog()
              self.dlg.pushButton.clicked.connect(self.select_output_file)

And after getting features in comboBox, I tried this:

# show the dialog
    self.dlg.show()
    # Run the dialog event loop
    result = self.dlg.exec_()
    # See if OK was pressed
    if result:
      filename = self.dlg.lineEdit.text()
      with open(filename, 'w') as output_file:
          layer = selectedlayer ##U already add a main layer as selectedLayer
          selectedFeature = self.dlg.comboBox.currentText
          layer.select(selectedFeature)
          writer = QgsVectorFileWriter.writeAsVectorFormat(layer, output_file, 'utf-8', layer.crs(),'ESRI Shapefile', onlySelected=True)
          selected_layer = iface.addVectorLayer(output_file, '', 'ogr')
          del(writer)

After this, I got following error

Traceback (most recent call last): File "C:\Users/DELL/AppData/Roaming/QGIS/QGIS3\profiles\default/python/plugins\get_map\get_map.py", line 226, in run writer = QgsVectorFileWriter.writeAsVectorFormat(layer, output_file, 'utf-8', layer.crs(),'ESRI Shapefile', onlySelected=True) TypeError: QgsVectorFileWriter.writeAsVectorFormat(): arguments did not match any overloaded call: overload 1: argument 2 has unexpected type '_io.TextIOWrapper' overload 2: argument 2 has unexpected type '_io.TextIOWrapper' overload 3: argument 2 has unexpected type '_io.TextIOWrapper'

How can I overcome this error by which I can export a shapefile of a particular feature?

Answer 1

Looking at the API Docs suggests that writeAsVectorFormat expects the 2nd argument to be a string containing the file name not a file object, which would match your error message.

writeAsVectorFormat(layer: QgsVectorLayer, fileName: str, fileEncoding: str, destCRS: QgsCoordinateReferenceSystem = QgsCoordinateReferenceSystem(), driverName: str = '', onlySelected: bool = False, datasourceOptions: Iterable[str] = [], layerOptions: Iterable[str] = [], skipAttributeCreation: bool = False, newFilename: str = '', symbologyExport: QgsVectorFileWriter.SymbologyExport = QgsVectorFileWriter.NoSymbology, symbologyScale: float = 1, filterExtent: QgsRectangle = None, overrideGeometryType: QgsWkbTypes.Type = QgsWkbTypes.Unknown, forceMulti: bool = False, includeZ: bool = False, attributes: Iterable[int] = [], fieldValueConverter: QgsVectorFileWriter.FieldValueConverter = None) → Tuple[QgsVectorFileWriter.WriterError, str]¶

Write contents of vector layer to an (OGR supported) vector format

Parameters

        layer (QgsVectorLayer) – layer to write

        fileName (str) – file name to write to

        fileEncoding (str) – encoding to use

        destCRS (QgsCoordinateReferenceSystem = QgsCoordinateReferenceSystem()) – CRS to reproject exported geometries
            to, or invalid CRS for no reprojection

        driverName (str = '') – OGR driver to use

        onlySelected (bool = False) – write only selected features of layer

        errorMessage – will be set to the error message text, if an error occurs while writing the layer

        datasourceOptions (Iterable[str] = []) – list of OGR data source creation options

        layerOptions (Iterable[str] = []) – list of OGR layer creation options

        skipAttributeCreation (bool = False) – only write geometries

        newFilename (str = '') – QString pointer which will contain the new file name created (in case it is different to
           fileName).

        symbologyExport (QgsVectorFileWriter.SymbologyExport = QgsVectorFileWriter.NoSymbology) – symbology to export

        symbologyScale (float = 1) – scale of symbology

        filterExtent (QgsRectangle = None) – if not None, only features intersecting the extent will be saved (added in QGIS 2.4)

        overrideGeometryType (QgsWkbTypes.Type = QgsWkbTypes.Unknown) – set to a valid geometry type to override the
         default geometry type for the layer. This parameter allows for
         conversion of geometryless tables to null geometries, etc (added in
             QGIS 2.14)

        forceMulti (bool = False) – set to True to force creation of multi* geometries (added in QGIS 2.14)

        includeZ (bool = False) – set to True to include z dimension in output. This option is only valid if overrideGeometryType
       is set. (added in QGIS 2.14)

        attributes (Iterable[int] = []) – attributes to export (empty means all unless skipAttributeCreation is set)

        fieldValueConverter (QgsVectorFileWriter.FieldValueConverter = None) – field value
        converter (added in QGIS 2.16)