Finding a more efficient way to execute a long-run python script

Question

I'm executing a python script which does these steps:

1. iterates through 19 features (makes pairs "each one with each other", order doesn't matter: A-B = B-A)
2. Creates Closest Facility Layer
3. Adds location points
4. Solves Closest Facility route
5. Exports into single .shp for each pair

I need to get a polyline for each of the pairs of 19 combinations. This will result (if I count correctly) in 19*18/2 = 174 shapefiles. When I run the script, it works fine until about 40th pair. Then it gets slower and slower. I let it run for about 3 hours and I got 142th pair...then ArcMap crashed with an error screen saying all my work is lost. If it ended alright I would then merge all the shapefiles into a single one with 174 features in it.

Is there any way to make the script more efficient or a way how to solve this problem?

This is the script:

 from collections import defaultdict
 import itertools
 import pprint

 import arcpy
 from arcpy import env
 import os

 ddict = defaultdict(list)
 for start,end in itertools.combinations(range(19), 2):
ddict[start].append(end)

try:
arcpy.CheckOutExtension("Network")
env.workspace = r"D:/Dokumenty/GISdata/PID"
env.overwriteOutput = True


inNetworkDataset = r"D:/Dokumenty/GISdata/PID/New/silnice_useky_krnap_ND.nd"
impedanceAttribute = "Length"
accumulateAttributeName = ["Length"]

for key,value in ddict.items():
    for v in value:
        inFacilities = r"PID/New/Obce_body_luzka" # melo by byt key
        inIncidents = r"PID/New/Obce_body_luzka" # melo by byt v
        outNALayerName = "Dvojice_bodu_{}_{}".format(key, v)
        outLayerFile = os.path.join(r"D:/Dokumenty/GISdata/output2", outNALayerName + ".lyr")
        NAResultObject = arcpy.na.MakeClosestFacilityLayer(inNetworkDataset,outNALayerName,impedanceAttribute,"TRAVEL_TO","",1, accumulateAttributeName,"NO_UTURNS")


        outNALayer = NAResultObject.getOutput(0)


        subLayerNames = arcpy.na.GetNAClassNames(outNALayer)
        #Stores the layer names that we will use later
        facilitiesLayerName = subLayerNames["Facilities"]
        incidentsLayerName = subLayerNames["Incidents"]


        import arcpy

        intable = "D:\Dokumenty\GISdata\PID\New\Obce_body_luzka.dbf"

        fields = arcpy.ListFields(intable)

        fieldinfo = arcpy.FieldInfo()


        for field in fields:
            fieldinfo.addField(field.name, field.name, "VISIBLE", "")
        arcpy.MakeTableView_management(intable, "temp_table", "FID = {}".format (key), "", fieldinfo)
        arcpy.MakeTableView_management(intable, "temp_table2", "FID = {}".format (v), "", fieldinfo)
        fieldMappings = arcpy.na.NAClassFieldMappings(outNALayer, facilitiesLayerName, False, fields) 
        arcpy.na.AddLocations(outNALayer, facilitiesLayerName, "temp_table", fieldMappings, "")
        arcpy.na.AddLocations(outNALayer, incidentsLayerName, "temp_table2", "", "")

        arcpy.na.Solve(outNALayer)

                arcpy.management.SaveToLayerFile(outNALayer,outLayerFile,"RELATIVE")
        routesLayer = arcpy.mapping.ListLayers(outNALayer, "routes")[0]
        arcpy.FeatureClassToShapefile_conversion(routesLayer, r"D:/dokumenty/gisdata/output4")

print "Script completed successfully"

except Exception as e:

import traceback, sys
tb = sys.exc_info()[2]
print "An error occured on line %i" % tb.tb_lineno
print str(e)