Populating layer field with dict.values() in PyQGIS 3?

Question

I've coded the script below in PyQGIS 3 to get the azimuth of starting or ending points for a line layer that touches a border. It works fine, but I want to populate the azimuth field layer with the value from azDict and doesn't work.

from shapely.geometry import LineString, Point, Polygon, LinearRing

lLayer = QgsProject.instance().mapLayersByName('roads')[0]
pLayer = QgsProject.instance().mapLayersByName('aux_point')[0]
polLayer = QgsProject.instance().mapLayersByName('aux_boundary')[0]
feat = QgsFeature()
pr = pLayer.dataProvider()
vDict = {} 
azDict = {}

# iterates in vertex lines to get dict = {Point1:Point2}
for road in lLayer.getFeatures():
    if road.geometry() is not None:
        line = road.geometry().asMultiPolyline()
        for vrtx in line:
            stp = QgsPointXY(line[0][0]) #  start point
            scp = QgsPointXY(line[0][1]) #  second point
            vDict[stp] = vDict.setdefault(stp, scp)
            edp = QgsPointXY(line[-1][-1]) #  end point
            lbo = QgsPointXY(line[-1][-2]) #  last but one point
            vDict[edp] = vDict.setdefault(edp, lbo)

#  iterates in vDict to calculates the azimuth
for k,v in vDict.items():
    azim = k.azimuth(v)
    azDict[k] = azDict.setdefault(k,azim) #  gives a dict = {Point:Azimuth}

#  begin the spatial filter
for polygon in polLayer.getFeatures(): #  transforms my boundary in a shapely LinearRing
    if polygon.geometry() is not None:
        poly = polygon.geometry().asMultiPolygon()
pol = Polygon(poly[0][0]) #  creates a shapely polygon
linearring = LinearRing(list(pol.exterior.coords))

#  iterates in azDict to filter spatially
for k,v in azDict.items():
    if linearring.distance(Point(k)) < 1:
        orientation = pr.fieldNameIndex("azimuth")
        feat.setGeometry(QgsGeometry.fromPointXY(QgsPointXY(Point(k).x,Point(k).y)))
        pr.addFeatures([feat])
        #  try to write the azimuth in the field but doesn't works
        pLayer.startEditing()
        pLayer.changeAttributeValue(feat.id(), orientation, v)
    QgsProject.instance().addMapLayer(pLayer)
    pLayer.triggerRepaint()
    pLayer.commitChanges()

Am I losing something?

Answer 1

You could try an approach like this. I am not sure exactly what your azDict looks like, but I have created an example dictionary based on your comment, so if yours looks different, you may modify accordingly. Also I have created a memory layer with a field called 'Azimuth'. If you are working with an existing layer, you can ignore the first part of my script (which creates the memory layer and adds the 'Azimuth' field).

# just an example dictionary
azDict = {(131.5, -15.0): 99.9, (131.5, -14.75): 85.4, (131.5, -14.5): 93.5, (131.5, -14.25): 35.8, (131.5, -14.0): 78.3}
vl = QgsVectorLayer('Point?crs=EPSG:4326', 'Temp_Azimuth', 'memory')
pr = vl.dataProvider()
pr.addAttributes([QgsField('Azimuth', QVariant.Double)])
vl.updateFields()
# create an empty list to hold our features
feats = []
# create features, set their geometries from dictionary key tuple and store them in a list
for k, v in azDict.items():
    f = QgsFeature()
    geom = QgsGeometry().fromPointXY(QgsPointXY(k[0], k[1]))
    f.setGeometry(geom)
    feats.append(f)
# add features to vector layer
pr.addFeatures(feats)
# get and store ids of features
ids = [f.id() for f in vl.getFeatures()]
# get id of 'Azimuth' field
fld_id = vl.fields().lookupField('Azimuth')
# extract azimuth values from dictionary and store those in a list
vals = [v for k, v in azDict.items()]
val_idx = -1 # create an index to traverse the items in the value list
for i in ids:
    val_idx = val_idx + 1 # add 1 to list index for each iteration
    # store field and value in a dictionary
    atts = {fld_id: vals[val_idx]} # first index will be 0
    # set new attributes
    pr.changeAttributeValues({i: atts})
# load layer
QgsProject().instance().addMapLayer(vl)