Get UpStream Watersheds and PWS

# -*- coding: utf-8 -*-
# ---------------------------------------------------------------------------
# Get_UpStream.py
# Created on: 2020-09-09 
# By:  Michelle Hawks
# Description: Finds subwatersheds (HUC12) upstream from
#              selected subwatershed.
# ---------------------------------------------------------------------------

import arcpy

# need the full layer to select from, and the selected HUC12 value
theLyr = arcpy.GetParameterAsText(0)

huclst = []    
theField = 'HUC12'
theField1 = 'ToHUC'

# Process: Get Field Value
fieldlist = ['HUC12','ToHUC']
with arcpy.da.SearchCursor(theLyr,fieldlist) as cursor:
    for row in cursor:
        huc12 = row[0]
        tohuc = row[1]
del cursor
huclst.append(huc12)

# theLyr = "https://wmxbetatest.esri.com/server/rest/services/Hosted/Watersheds/FeatureServer/0"
theLyr = "https://usfs-dmsc-hst.esriemcs.com/server/rest/services/Hosted/F2FHUC12/FeatureServer/0"
theField = "huc12"
theField1 = "tohuc"
fieldlist = ["huc12", "tohuc"]
        
def getUpStrm(huc12):
    arcpy.AddMessage("Getting Up Stream")
    huclist_u = []
    huclist_u.append(huc12)
    huclist_up = []
    huclist_up.append(huclist_u)
    numsel = len(huclist_u)
    while numsel > 0:
        if len(huclist_u) > 1:
            where_clause = "{} IN {}".format(theField1, tuple(huclist_u))
        else:
            where_clause = "{} = '{}'".format(theField1, huclist_u[0])
        selLyr = (
            arcpy.SelectLayerByAttribute_management(
                theLyr, "NEW_SELECTION", where_clause
            )
        )[0]
        huclist_u = unique_values(selLyr)
        numsel = len(huclist_u)
        if numsel > 0:
            arcpy.AddMessage(huclist_u)
            huclist_up.append(huclist_u)
    arcpy.AddMessage("Finished Up Stream")
    return huclist_up

    
def unique_values(selLyr):
    with arcpy.da.SearchCursor(selLyr,fieldlist) as cursor:
        return sorted({row[0] for row in cursor})

huclist_up = getUpStrm(huc12)
huclist_upl = [item for items in huclist_up for item in items]

huclist_fulld = list(dict.fromkeys(huclist_upl)) 

final_sel = None
count = len(huclist_fulld)
if count > 1:
    where_clause = "{} IN {}".format(theField, tuple(huclist_upl))
    if count > 2000:
        listchunks = [
            huclist_fulld[x : x + 2000] for x in range(0, len(huclist_fulld), 2000)
        ]
        for x in range(0, len(listchunks)):
            nlst = listchunks[x]
            where_clause = "{} IN {}".format(theField, tuple(nlst))
            if x == 0:
                final_sel = arcpy.SelectLayerByAttribute_management(
                    theLyr, "NEW_SELECTION", where_clause
                )
                numsel = int(arcpy.GetCount_management(theLyr).getOutput(0))
            else:
                final_sel = arcpy.SelectLayerByAttribute_management(
                    theLyr, "ADD_TO_SELECTION", where_clause
                )
                numsel = int(arcpy.GetCount_management(theLyr).getOutput(0))
elif count != 0:
    where_clause = "{} = '{}'".format(theField, huclist_up[0])
else:
    where_clause = None
    
if not final_sel and where_clause:
    final_sel = (
        arcpy.SelectLayerByAttribute_management(theLyr, "NEW_SELECTION", where_clause)
    )[0]
    arcpy.SetParameter(1, final_sel)