topic Re: ListFields after GetCount throws error in Python Questions

ListFields after GetCount throws error

TrevorWeiland — Tue, 21 Oct 2025 16:05:23 GMT

I'm trying to loop through all fields in all Layers in a Pro Project and am getting a weird error that only happens when I first check for data in the Layer.

This code works but unnecessarily (for my purposes) loops through all fields when the Layer is empty (slow):

aprx = fullPathToProProject.aprx m = (arcpy.mp.ArcGISProject(aprx)).listMaps()[0] for lyr in m.listLayers: for field in arcpy.ListFields(lyr): print(field.name)

This skips Layers with no data (much faster) but fails if the Layer actually has data:

aprx = fullPathToProProject.aprx m = (arcpy.mp.ArcGISProject(aprx)).listMaps()[0] for lyr in m.listLayers: if int(arcpy.management.GetCount(lyr).getOutput(0)) > 0: for field in arcpy.ListFields(lyr): print(field.name)

Error Message:
Traceback (most recent call last):
File "<fullPythonFilePath>.py", line 5, in <module>
for field in arcpy.ListFields(lyr):
File "C:\Program Files\ArcGIS\Pro\Resources\ArcPy\arcpy\__init__.py", line 1228, in ListFields
return gp.listFields(dataset, wild_card, field_type)
File "C:\Program Files\ArcGIS\Pro\Resources\ArcPy\arcpy\geoprocessing\_base.py", line 378, in listFields
self._gp.ListFields(*gp_fixargs(args, True)))
OSError: "<layerName>" does not exist

Any suggestions on testing for data and then listing fields?

Re: ListFields after GetCount throws error

DanPatterson — Tue, 21 Oct 2025 21:32:07 GMT

I would adjust your code to check to ensure that you are working with FeatureClasses just in case you have a layer that doesn't the requirements for listFields

Layer—ArcGIS Pro | Documentation

using isFeatureLayer between lines 3 and 4

Re: ListFields after GetCount throws error

HaydenWelch — Wed, 22 Oct 2025 15:18:52 GMT

If you want speed, you can get a big bump by not getting the count, but instead just trying to iterate a cursor and immediately returning True if there's rows. Couple that with Dan's isFeatureLayer check and you can do everything in a pretty compact filter operation:

import arcpy def has_rows(lyr: arcpy.mp.Layer) -> bool: if not lyr.isFeatureLayer: return False with arcpy.da.SearchCursor(lyr, 'OBJECTID') as cur: for _ in cur: return True return False def get_field_names(map: arcpy.mp.Map) -> None: for lyr in filter(has_rows, map.listLayers()): for field in arcpy.ListFields(lyr): print(field.name) if __name__ == '__main__': aprx = '<project>.aprx' m = arcpy.mp.ArcGISProject(aprx).listMaps()[0] get_field_names(m)

If you have broken layers in a map, you can also make sure that the feature layer has a valid datasource:

def has_rows(lyr: arcpy.mp.Layer) -> bool: if not lyr.isFeatureLayer or lyr.isBroken: return False with arcpy.da.SearchCursor(lyr, 'OBJECTID') as cur: for _ in cur: return True return False

Re: ListFields after GetCount throws error

EdMorris — Thu, 23 Oct 2025 11:21:05 GMT

Hi Trevor

I think you may also want to add a pair of brackets ( ) after m.listLayers as listLayers() is a method on the Map class:

Map—ArcGIS Pro | Documentation

Re: ListFields after GetCount throws error

TrevorWeiland — Wed, 07 Jan 2026 19:08:56 GMT

yes, i messed up the copy and paste.