Atribute index out of bounds [0;0] when connecting points of two point layers using PyQGIS

Question

I am currently writing an Python script within QGIS to connect points of two specific point layers:

Attributes of point layer 1:

Attributes of point layer 2:

For each point in point-layer1, the python script loops over all points of point-layer2 and compares the attribute "direction" (of point-layer1) with the attribute "location" (of point-layer2). If they are equal, a new line should be created and stored into the output line-layer (together with the "lineID" (a line counter) and the direction name + location name).

Here is my Python Script:

# name : ConnectPointsByValue_script
# date : 27.12.2017
# description: connects points from evis with points of location_coordinates
#       if the attributes "direction" and "location" are equal

from PyQt4.QtCore import QVariant
from qgis.core import *
from PyQt4.QtCore import *

#***********Constants
#
LINEID = 'lineID'
POINTID1 = 'pointID_Location'
POINTID2 = 'pointID_Direction'
#
#***********

# input parameters 
##Counters=vector
##Locations=vector

inputLayerCounters = processing.getObject(Counters)
inputLayerLocations = processing.getObject(Locations)

crs = inputLayerCounters.crs().toWkt()

# Create the output layer
outLayer = QgsVectorLayer('Linestring?crs='+ crs, 'connector_lines2' , 
'memory')
outdp = outLayer.dataProvider()


#get the field index
outLineID = outdp.fieldNameIndex(LINEID)
outID1 = outdp.fieldNameIndex(POINTID1)
outID2 = outdp.fieldNameIndex(POINTID2)
lineIDcnt = 0


# loop through points of iCounters and connect each point with the matching 
location point
for feat1 in inputLayerCounters.getFeatures():
   geom1 = feat1.geometry()

   #loop all points from iLocations
   for feat2 in inputLayerLocations.getFeatures():
      geom2 = feat2.geometry()

      # get the feature's attributes
      attrs1 = feat1.attributes()
      idx1 = inputLayerCounters.fieldNameIndex('direction')
      attrs2 = feat2.attributes()
      idx2 = inputLayerLocations.fieldNameIndex('location')

      #check if attributes are equal
      if feat1.attributes()[idx1] == feat2.attributes()[idx2]:
          lineIDcnt +=  1

          #if true: create line and add to output line layer
          connector = QgsFeature(outLayer.pendingFields())
          connector.setGeometry(QgsGeometry.fromPolyline([geom1.asPoint(),
                                                    geom2.asPoint()]))

          #record the IDs
          res = connector.setAttribute(outLineID, lineIDcnt)
          res = connector.setAttribute(outID1, feat1.attributes()[idx1])
          res = connector.setAttribute(outID2, feat2.attributes()[idx2])
        
          #add the feature to the layer
          res = outdp.addFeatures([connector])

        
 # Add the layer to the Layers panel
 QgsMapLayerRegistry.instance().addMapLayer(outLayer)

 print "Done .. "

If I execute this script, I get an error which says:

attribute index -1 out of bounds [0;0]

I think I am doing something wrong with indexing the attributes of my points. Any suggestions on how to solve this?

Answer 1

It does not look like you are adding attributes to your memory layer, try:

from PyQt4.QtCore import QVariant

# Create the output layer
outLayer = QgsVectorLayer('Linestring?crs='+ crs, 'connector_lines2', 'memory')
outLayer.startEditing()
outLayer.dataProvider().addAttributes([
                            QgsField("lineID", QVariant.String),
                            QgsField("pointID_Location", QVariant.String),
                            QgsField("pointID_Direction", QVariant.String)
                            ])
outLayer.updateFields()
outLayer.commitChanges()