I have a list of a 2 layers (nfhl_fld_haz_features, prelim_fld_haz_features) and a feature class (master_merge) that I want to perform a union on:

 wkflw2_union = arcpy.Union_analysis([master_merge, nfhl_fld_haz_features, prelim_fld_haz_features], wkflw2_union_output)

I keep getting the following error:

Traceback (most recent call last):

File "", line 1, in wkflw2_union = arcpy.Union_analysis([master_merge, nfhl_fld_haz_features, prelim_fld_haz_features], wkflw2_union_output)

File "C:\Program Files\ArcGIS\Pro\Resources\ArcPy\arcpy\analysis.py", line 734, in Union raise e

File "C:\Program Files\ArcGIS\Pro\Resources\ArcPy\arcpy\analysis.py", line 731, in Union retval = convertArcObjectToPythonObject(gp.Union_analysis(*gp_fixargs((in_features, out_feature_class, join_attributes, cluster_tolerance, gaps), True)))

File "C:\Program Files\ArcGIS\Pro\Resources\ArcPy\arcpy\geoprocessing_base.py", line 496, in return lambda *args: val(*gp_fixargs(args, True))

RuntimeError: Object: Error in executing tool

I don't see any issue with using a list, but could this error be due to using a feature class mixed with 2 layers? Or could this be something else (the main files come from a network drive)

  • To confirm, all three inputs are polygons? (And you can perform a test with your union to answer the question about mixing feature classes and layers by making a layer from the third input.)
    – SMiller
    Oct 16, 2018 at 13:59
  • Yes, they are all polygons. I've got a suspicion that this is some kind of network or server issue related to grabbing the files. I've had a similar issue before where someone else was accessing the same source file and a Runtime Error was thrown.
    – gwydion93
    Oct 16, 2018 at 14:51

1 Answer 1


I think it would be better to have parameters like file paths in input list. As far as understood master_merge is something like r"D:\work\file.gdb\master_merge" and let it be like this.

Paths to layers can be obtained with Describe function and catalogPath method. So you have:

master_merge = r"D:\work\file.gdb\master_merge"
wkflw2_union_output r"D:\work\file.gdb\union_out"

nfhl_fld_fc = arcpy.Describe('nfhl_fld_haz_features').catalogPath
prelim_fld_fc = arcpy.Describe('prelim_fld_haz_features').catalogPath

wkflw2_union = arcpy.Union_analysis([master_merge, nfhl_fld_fc, prelim_fld_fc], wkflw2_union_output)

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