I like Joshua Bixby 's code as it is simple. When you are in the UpdateCursor, just use the first 6 characters of the parcel id to check if it is in the original list, then set the flag. Here is that approach for you to test.
import arcpy
from collections import Counter
tbl = r'C:/Temp/ParcelNumberSample2.dbf'
parcel_count = Counter(
(pid[:6] for pid, in arcpy.da.SearchCursor(tbl,"PARCEL_NO"))
)
original = []
for pid,cnt in parcel_count.items():
if cnt == 1:
original.append(pid)
with arcpy.da.UpdateCursor(tbl,["PARCEL_NO","Org_Par"]) as cursor:
for row in cursor:
if row[0][:6] in original:
row[1] = 'Orig'
else:
row[1] = 'N'
cursor.updateRow(row)
If you find that you do need the object id to do some other things, here's and updated version of my code that may give you some ideas. I used where OBJECTID IN ( nnn, nnn) in my SQL; you may need to make adjustments for your version. I was also testing with a file geodatabase where you might be testing with a shapefile.
import arcpy
tbl = r'C:/Temp/ParcelNumberSample2.dbf' # use your table name
# read oid and parcel_id into dictionary
parcels = [[r[0],r[1]] for r in arcpy.da.SearchCursor(tbl, ['PARCEL_NO', 'OBJECTID'])] # use your field names
# print parcels
# empty dictionaries for parents and children
parentFound = {} # format: { parent parcel id : object id }
childFound = {} # format: { parent parcel id : ( object id, count of items) }
for p in parcels:
parent = p[0][:6]
# print parent
if len(p[0]) > len(parent):
if parent in childFound.keys():
childFound[parent] = (p[1], 1 + childFound[parent][1] )# this will be last child found (by objectid)
else:
childFound[parent] = (p[1], 0)
else:
parentFound[parent] = p[1] # this will be last parent found (by objectid)
# print parentFound
# print childFound
objID = [] # empty list for object ids
for k in parentFound.keys():
if k not in childFound.keys():
# print k, parentFound, "parent is orig" # this is the parcelid and objectid of parent parcels, add to a list
objID.append(parentFound)
for k in childFound.keys():
if k not in parentFound.keys():
if childFound[1] < 1:
# print k, childFound[0], "child is orig" # this would be the parent parcelid that was NOT found, add to the list also
objID.append(childFound[0])
# print sorted(objID)
where = "OBJECTID IN ({})".format(str(sorted(objID)).strip('[]')) # substitute name of object id field
with arcpy.da.UpdateCursor(tbl,["OBJECTID","Org_Par"], where_clause=where) as cursor:
for row in cursor: # this will just update the rows where an original parcel id was found
print row
row[1] = 'Orig'
cursor.updateRow(row)
