Using dictionary and cursors to calculate a field based on values from another table - KeyError [0]

Question

I'm new to dictionaries and am still a Python beginner. I'm trying to update field(s) based off of field values in another table using the OID field as a key. The search cursor dictionary has been filtered down (in an effort to conditionally update the values in the Line_Count_13_8 field) with a where clause for the portion of the script where I am receiving an error. I am getting a KeyError: [0] error on this line: if search_feats_138[0] == upd_row[0]: ‍‍‍ Here is the whole block: import arcpy from arcpy import env import time start = time.time() print start print "Start" arcpy.env.OverwriteOutput = True subLayer='C:\Topo_Check_Tess_V5.gdb\Sub' transLayer='C:\Topo_Check_Tess_V5.gdb\TL' ppLayer='C:\Topo_Check_Tess_V5.gdb\PP' pp_trans_GUJoin ='C:\Topo_Check_Tess_V5.gdb\pp_trans_GU_SpatialJoin' SubLayer_pp_trans_GUJoin = 'C:\Topo_Check_Tess_V5.gdb\SubLayer_pp_trans_GUSpatialJoin' arcpy.SpatialJoin_analysis ("SubLayer_Layer", "pp_trans_GUJoin_Layer", SubLayer_pp_trans_GUJoin, 'JOIN_ONE_TO_ONE', 'KEEP_ALL', fieldMappings, 'WITHIN_A_DISTANCE', .000002) ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ This section works: #add in Line_Count field arcpy.AddField_management(subLayer, "Line_Count", "SHORT", "", "", "", "", "NULLABLE", "NON_REQUIRED", "") search_feats = {f[0]:f[1] for f in arcpy.da.SearchCursor(SubLayer_pp_trans_GUJoin,["OBJECTID","Join_Count"])} with arcpy.da.UpdateCursor(subLayer,["OBJECTID","Line_Count"]) as upd_cur: for upd_row in upd_cur: upd_row[1] = search_feats[upd_row[0]] upd_cur.updateRow(upd_row) print "Line_Counts Updated" del upd_cur‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ This section does not work - KeyError: [0] on line 13: #add in Line_Count_13_8 field arcpy.AddField_management(subLayer, "Line_Count_13_8", "SHORT", "", "", "", "", "NULLABLE", "NON_REQUIRED", "") #where clause where_13_8 = ' "VT" = 13.8 ' #arcpy.MakeFeatureLayer_management(SubLayer_pp_trans_GUJoin, "Sub_PP_Trans_Join_13_8", where_13_8) search_feats_13_8 = {f[0]:f[1] for f in arcpy.da.SearchCursor(SubLayer_pp_trans_GUJoin,["OBJECTID","Join_Count"], where_13_8)} with arcpy.da.UpdateCursor(subLayer,["OBJECTID","Line_Count_13_8"]) as upd_cur: for upd_row in upd_cur: if search_feats_13_8[0] == upd_row[0]: upd_row[1] = search_feats_13_8[upd_row[0]] else: upd_row[1] = 0 upd_cur.updateRow(upd_row) print "Line_Count_13.8 Updated" del upd_curl end = time.time() print (end - start)/60‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ Any suggestions? Thanks in advance!

TessOldemeyer · Answer

Thanks! This totally helps. The following ended up doing the trick and replaces lines 13-16. upd_row[1] = search_feats_13_8.get(upd_row[0], 0)‍

JoshuaBixby · Answer

I think you want line 13 to be: if search_feats_13_8.get(upd_row[0], None) == upd_row[0]:‍‍‍‍ Without using a defaultdict, the problem you will have comparing keys is the error that will be generated when a key isn't present. Using the .get() method and a default value gets around this problem. Overall though, I am a fan of using defaultdict.