Error writing memory layer to shapefile in QGIS

Question

I have created a memory polygon layer in my QGIS plugin. Then I added a buffer based on a point. I can see the ploygon memory layer in the map canvas and I can save it to a shapefile from the main GUI. But when I try to save it with the following code, it doesn't work. What am I doing wrong?

(please forgive my beginner-style coding)

uri = "Polygon?field=id:integer&index=yes&crs=27700"
self.polyLayer = QgsVectorLayer(uri, "Study area", "memory")
self.provider = self.polyLayer.dataProvider()
QgsMapLayerRegistry.instance().addMapLayer(self.polyLayer)

# create buffer feature
featurepoly = QgsFeature()
featurepoly.setGeometry(QgsGeometry.fromPoint(QgsPoint(self.point.x(),self.point.y())).buffer(200,1000, 1, 1, 1.0))
self.polyLayer.startEditing()
self.polyLayer.addFeature(featurepoly, True)
self.polyLayer.commitChanges()

# getting the new buffered memory layer
poly = self.iface.activeLayer()

prov = poly.dataProvider()
fields = prov.fields()

dir_poly = self.plugin_dir + '/data/poly_temp.shp'
writer = QgsVectorFileWriter(dir_poly, "CP1250", fields, prov.geometryType(),
                                     prov.crs(), "ESRI shapefile")
if writer.hasError() != QgsVectorFileWriter.NoError:
            self.iface.messageBar().pushMessage("Error when creating shapefile: ", str(writer.hasError()))

geometry = poly.geometry()
feature = QgsFeature()
feature.setGeometry(geometry)
writer.addFeature(feature)
del writer

Answer 1

You may need to have this at the top of your code:

from PyQt4.QtCore import *

Or it might be the path you are giving it:

http://docs.qgis.org/testing/en/docs/pyqgis_developer_cookbook/vector.html

that documentation just has a file name, you could give it a path instead and then it works.