If I don't rebind layer to the result from SelectLayerByAttribute, then the call to getSelectionSet() will return no selection. To switch gears a bit, let me tell you a bit more about my actual project.
In my real python toolbox script, I take a feature layer as input and rely on the layer selection to process only certain features. I will try to provide the important pieces of code so you can see how it works and where it fails.
Starting out, I use a function to define the parameters:
def make_param(disp_name, p_name, data_type, default_val=None, p_type="Required", p_dir="Input"):
param = arcpy.Parameter(
displayName=disp_name,
name=p_name,
datatype=data_type,
parameterType=p_type,
direction=p_dir,
)
param.value = default_val
return param
Then, in the toolbox init, the layer parameter is defined like so:
self.parameters = [
make_param("AOI Polygon Layer", "in_lyr", "GPFeatureLayer")
]
In the tool's execute method, the argument is assigned to a local variable like so:
in_lyr = parameters[0].value
Shortly thereafter, I check for a selection and raise an exception if there is none:
# check for selection on AOI layer
selection = in_lyr.getSelectionSet()
if not selection:
arcpy.AddError("You must select AOI features to evaluate!")
raise NoSelectionError("There was no selection in the AOI layer")
Then, I open a search cursor on the layer and create a dictionary that will be used to store the results from other tools:
with arcpy.da.SearchCursor(in_lyr, ["AOI_ID"]) as cursor:
result = {row[0]: {"AOI_ID": row[0]} for row in cursor}
At this point, I run spatial join because later steps depend on its output. You will notice at the end that I've now included a line to restore the selection back to its original state after this tool is run.
# spatial join to check for overlaps in the AOI polygons if zonal stats to be used
# creating the spatial joined feature class now, otherwise it might be done repeatedly
if option_sl_score or option_gi_scores or option_canopy_cover:
arcpy.AddMessage("Checking for overlap in input AOIs ...")
arcpy.analysis.SpatialJoin(
in_lyr,
in_lyr,
"out_spatial_join",
"JOIN_ONE_TO_MANY",
match_option="WITHIN_A_DISTANCE",
search_radius=-0.1,
)
# spatial join clears layer selection, so we restore it
in_lyr.setSelectionSet(list(selection))
If line 14 above is omitted, the selection in the layer will be cleared and the code breaks downstream because I've only started gathering results for a selection of features. For example:
arcpy.TabulateIntersection_analysis(
in_zone_features=in_lyr,
zone_fields="AOI_ID",
in_class_features=wmo_bdry,
out_table="wmo_tab",
class_fields="NAME_TXT",
)
wmo_flds = ["AOI_ID", "NAME_TXT", "PERCENTAGE"]
wmo_d = {"3": "MCWD", "6": "MWMO", "7": "BCWMC", "8": "SCWMC"}
# store results in result dict
with arcpy.da.SearchCursor("wmo_tab", wmo_flds) as cursor:
for row in cursor:
aoi_id, wmo_id, perc = row
wmo = wmo_d.get(wmo_id, "OTHER")
pct_fld = f"PCT_{wmo}"
result[aoi_id][pct_fld] = round(perc, 2)
If the selection is not restored, tabulate intersection will operate on all features and the tool will fail with a KeyError exception because the aoi_id does not exist in the result dictionary. Of course, this problem can be resolved with some tweaks to the script, but my reason for posting is to either figure out if I am using the layer object from the parameter inappropriately or to determine that this is indeed a bug in arcpy.
