qgis script to add nodes bearigns and diastances as attribute

nodes_text.py

##input_polygons=vector
##node_field_name=string

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

# get layer
layer = processing.getObjectFromUri(input_polygons)
progress.setInfo(node_field_name)

print(layer.crs().authid())
crs_geo = layer.crs().geographicFlag()
if crs_geo:
    setInfo("Layer is in LatLong, no distance calculation!")
    
# test what we can do
caps = layer.dataProvider().capabilities()

# add field for ndoes if not existing
if caps & QgsVectorDataProvider.AddAttributes:
    field_names = [field.name() for field in layer.pendingFields() ]
    if node_field_name not in field_names: 
        res = layer.dataProvider().addAttributes([QgsField(node_field_name, QVariant.String)])
        layer.updateFields()
    nodes_field_index = (field_names.index(node_field_name))

# iterate over features and calculate node bearing and distances...
iter = layer.getFeatures()
n_features = layer.featureCount()

for feature in iter:
    # retrieve every feature with its geometry and attributes
    # fetch geometry
    geom = feature.geometry()
    print "Feature ID %d: " % feature.id()
    if geom.type() == QGis.Polygon:
        poly = geom.asPolygon()
        # xy list of first ring of poly, assuming there is only one!
        xy = poly[0]
        for i in range(len(poly[0]) - 1):
            if crs_geo:
                dist = NA
            else: 
                dist = round(xy[i].sqrDist(xy[i+1]) /1000., 2)
            nodes_text = "node==%i: x=%2d, y=%2d, azim=%6.1f, dist=%6.1f km" % (i, xy[i].x(), xy[i].y(), xy[i].azimuth(xy[i+1]), dist)
            #print(nodes_text)
            attr = {nodes_field_index : nodes_text}
            # print(attr)
            layer.dataProvider().changeAttributeValues({ i : attr })
   # fetch & print attributes
    attrs = feature.attributes()
    print attrs