ListFields after GetCount throws error

Question

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 ".py", line 5, in 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: "" does not exist Any suggestions on testing for data and then listing fields?

TrevorWeiland · Answer

yes, i messed up the copy and paste.

EdMorris · Answer

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

Hayden Welch · Answer

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