Setting border-style to 'no pen' using QgsGraduatedSymbolRendererV2

Question

I am developing a QGIS plugin that, after a series of inputs, will produce a thematic map using the QgsGraduatedSymbolRendererV2. Because the polygon are very small, the boarders make it such that when zoomed out the entire map almost looks completely black. I want to remove the boarders to do this but no documentation or form I have found have demonstrated how to do this. Below is what I have to create the thematic map, but somewhere in there I need to set the border style to 'no pen'. But how!?

  uri = QgsDataSourceURI()
  # set host name, port, database name, username and password
  uri.setConnection("localhost", "5432", "public", "postgres", "password")

  uri.setDataSource("susip", str(filename)+"_mce_results", "the_geom")
  layer = QgsVectorLayer(uri.uri(), str(filename)+"_mce_results", "postgres")

  fieldName = "score"
  fieldIndex = layer.fieldNameIndex( columnName )
  provider = layer.dataProvider()
  numberOfClasses = 10
  color1 = QColor("red")  
  color2 = QColor("green")
  color3 = QColor("white")
  ramp = QgsVectorGradientColorRampV2(color1, color2)

  renderer = QgsGraduatedSymbolRendererV2.createRenderer(layer, columnName, numberOfClasses, QgsGraduatedSymbolRendererV2.Quantile, QgsSymbolV2.defaultSymbol(layer.geometryType()), ramp)

  layer.setRendererV2( renderer )
  QgsMapLayerRegistry.instance().addMapLayer( layer )

Answer 1

This question is very old but, I found the answer. It's necessary for each symbol (QgsFillSymbolV2 for polygon geometry) to use 'setOutputUnit' method to set it with value equal 1. Complete code is:

from qgis.PyQt.QtGui import QColor

layer = iface.activeLayer()

fieldName = "FID"

provider = layer.dataProvider()
numberOfClasses = 10
color1 = QColor("red")  
color2 = QColor("green")
color3 = QColor("white")

ramp = QgsVectorGradientColorRampV2(color1, color2)

renderer = QgsGraduatedSymbolRendererV2.createRenderer(layer, 
                                                       fieldName, 
                                                       numberOfClasses, 
                                                       QgsGraduatedSymbolRendererV2.Quantile, 
                                                       QgsSymbolV2.defaultSymbol(layer.geometryType()), 
                                                       ramp)

symbols = renderer.symbols()

for symbol in symbols:
    symbol.setOutputUnit(1) #1 is for no pen

layer.setRendererV2( renderer )

layer.triggerRepaint()

I tried it out with this shapefile:

After running the code at Python Console of QGIS I got:

It works!