Network Analyst and ArcPy: finding k-alternate path

k_alternate_path.py

'''Python add-in that will find multiple k-alternate paths between a given number of stops.
This code is supposed to be run in ArcMap map document with a Route Network Analysis layer
named Route with at least two stops loaded. The impedance attribute name is read from a
Route solver properties object.'''

import os
import arcpy
import arcpy.mapping as mp
import pythonaddins

class ComboBoxClass1(object):
    """Implementation for kAlternativeRoutes_addin.combobox (ComboBox)"""
    def __init__(self):
        self.items = ["1", "2", "3", "4", "5"]
        self.editable = True
        self.enabled = True
        self.dropdownWidth = 'WW'
        self.width = 'WW'
    def onSelChange(self, selection):
        pass
    def onEditChange(self, text):
        pass
    def onFocus(self, focused):
        pass
    def onEnter(self):
        k = int(self.value)
        mxd = mp.MapDocument('current')
        df = mp.ListDataFrames(mxd)[0]
        route_NAlayer = arcpy.mapping.Layer("Route")
        barriers_NAlayer = arcpy.mapping.Layer("Route\Line Barriers")

        #cleaning all existing barriers from previous runs
        arcpy.DeleteFeatures_management(barriers_NAlayer)
        out_k_routes = r'in_memory\k_route'

        #solve Route
        arcpy.Solve_na(in_network_analysis_layer="Route")
        routes_solved = arcpy.mapping.ListLayers(route_NAlayer, "Routes")[0]

        #create the first route and keep in memory
        arcpy.CopyFeatures_management(routes_solved, out_k_routes)
        arcpy.AddMessage('done original solve')

        for i in xrange(k-1):
            arcpy.AddMessage('doing K {}'.format(i+1))

            impedance = arcpy.na.GetSolverProperties(route_NAlayer).impedance
            field_mappings = arcpy.na.NAClassFieldMappings(route_NAlayer, 'Line Barriers')
            field_mappings["BarrierType"].defaultValue = 1 #Scaled Cost type
            #factor by which attr_impedance of road links will be multiplied
            field_mappings["Attr_{0}".format(impedance)].defaultValue = 2.5
            #cleaning up all barriers
            arcpy.DeleteFeatures_management(barriers_NAlayer)

            #loading previously solve route(s) as barriers
            arcpy.AddLocations_na(in_network_analysis_layer=route_NAlayer,
                                  sub_layer='Line Barriers', in_table=out_k_routes,
                                  field_mappings=field_mappings)

            #solve with barrier(s)
            barrier_count = arcpy.GetCount_management(barriers_NAlayer)
            arcpy.AddMessage('Number of barriers before solve is: {}'.format(barrier_count))
            arcpy.Solve_na(in_network_analysis_layer="Route")
            routes_solved = arcpy.mapping.ListLayers(route_NAlayer, "Routes")[0]

            #append to the output all routes which will serve as barriers layer
            arcpy.Append_management(routes_solved, out_k_routes, 'NO_TEST')

        #generate output routes alternatives in a feature class
        arcpy.CopyFeatures_management(out_k_routes, os.path.join(arcpy.env.scratchGDB,
                                                                 'AlternativeRoutes'))
        arcpy.mapping.RemoveLayer(df, mp.Layer('k_route'))
        arcpy.Delete_management(out_k_routes)
    def refresh(self):
        pass