qgis - Join table field with shapefile programatically (via PyQgis)?

The following is currently unsuccessful at fulfilling a table field join to a point shapefile in Qgis.
All instances of the join object will print the proper values, and no error is flagged when processing - but the target layer does not exhibit any effect.

Something missing?

    Heads = QgsVectorLayer(headCSV, 'Heads', 'ogr')

    QgsMapLayerRegistry.instance().addMapLayer(Heads)
    self.iface.legendInterface().setLayerVisible(Heads,False)
    grid = ftools_utils.getMapLayerByName(unicode('Grid'))
    joinObject = QgsVectorJoinInfo()
    joinObject.targetFieldName = str('ID')
    joinObject.joinLayerID = Heads.id()
    joinObject.joinFieldName = str('cellID')
    grid.addJoin(joinObject)
    grid.reload()

UPDATE:

The following returns 'None'. I expect this is actually supposed to return the field names to be joined? (e.g. - a clue to the mistake)

    print joinObject.joinFieldNamesSubset()

FURTHER UPDATE:

Added the following, and now the previous update command returns the accurate fields to be joined - yet the destination layer does not show 'joined' fields...

    joinObject.setJoinFieldNamesSubset(['someFieldName'])

Answer

This has worked for me:

# Get input (csv) and target (Shapefile) layers

shp=iface.activeLayer()
csv=iface.mapCanvas().layers()[0]

# Set properties for the join
shpField='code'
csvField='codigo'
joinObject = QgsVectorJoinInfo()
joinObject.joinLayerId = csv.id()
joinObject.joinFieldName = csvField
joinObject.targetFieldName = shpField

shp.addJoin(joinObject)

The error you are facing is, believe it or not, by a typo in joinLayerId. The question is, why QGIS doesn't throw an error there?