Vjylku

I am an absolute beginner in Python programming. Despite numerous attempts to rectify I am constantly finding new errors in the script below. Can anyone help please?

Network analysis=group

Shortest paths=name

Road_layer=vector line

Start_points=vector point

End_points=vector point

Shortest_paths=output vector

from PyQt4.QtCore import QVariant

from qgis.core import QGis, QgsFeature, QgsGeometry, QgsField, QgsFields
from qgis.networkanalysis import (QgsLineVectorLayerDirector,
QgsDistanceArcProperter, QgsGraphBuilder, QgsGraphAnalyzer)

from processing.core import GeoAlgorithmExecutionException
from processing.tools.vector import VectorWriter
layerRoads = processing.getObjectFromUri (Road_Layer)
layerStartPoints = processing.getObjectFromUri (Start_points)
layerStopPoints = processing.getObjectFromUri (End-points)
if layerStartPoints.featureCount () != layerStopPoints. featureCount():
GeoAlgorithmExecutionException (
'Number of features in start and end point layers should be equal!')
progress.setInfo ('Gathering start and stop points')

feats=layerStartPoints.getFeatures()

points=[f.geometry() .asPoint() for f in feats]



feats=layerStopPoints .getFeatures()

tmp=[f.geometry() .asPoint() for f in feats]



fields=QgsFields ()

fields.append(QgsField ('id', QVariant.Int, '',10))

fields.append(QgsField('startPoint', QVariant.String, '', 254))

fields.append(QgsField('endPoint', QVariant.String, '', 254))

fields.append(QgsField('length', QVariant.Double,'',20,7))



writer=VectorWriter(Shortest_paths, None, fields.toList(), QGis.WKBLineString, layerRoads.crs())

director=QgsLineVectorLayerDirector(layerRoads, -1, '', '', '', 3)

properter=QgsDistanceArcProperter()

director.addProperter(properter)

builder=QgsGraphBuilder(layerRoads.crs())

progress.setInfo('Generating road graph...')

tiedPoints=director.makeGraph(builder, points)

graph=builder.graph()

del points

count=layerStartPoints.featureCount()

total=100.0/float(count)



ft=QgsFeature()

ft.setFields(fields)

progress.setInfo('Finding shortest paths')
for i in xrange(count):
nStart = tiedPoints[i]
nStop = tiedPoints[count + i]
idxStart = graph.findVertex(nStart)
idxStop = graph.findVertex(nStop)

tree, cost = QgsGraphAnalyzer.dijkstra(graph, idxStart, 0)



if tree[idxStop] == -1:

    progress.setInfo('No path found from point ({:.6f},{:.6f})'

        'to point ({:.6f},{:.6f})'.format(

            nStart.x(), nStart.y(), NStop.x(), nStop.y()))

else:

    nodes = []

    curPos = idxStop

    while curPos != idxStart:

        nodes.append (graph.vertex(

            graph.arc (tree [curPos]. inVertex())).point())

        curPos=graph.arc(tree[curPos]).outVertex()



    nodes.append (nStart)

    nodes.reverse ()



    ft.setGeometry(QgsGeometry .fromPolyline (nodes))

    ft ['id'] = i

    ft ['startPoint']='({:.6f},{:.6f}).format(nStart.x(),nStart.y())

    ft['endPoint']  =   """({:.6f},{:.6f})""" .format (nStop.x(),nStop.y())

    ft['length']=ft.geometry() .length()

    writer.addFeature(ft)



    progress.setPercentage (int(i*total))

del graph
del writer