Displays the key values that are duplicates in a list of attribute field values.

displayDuplicateValuesInField.py

#
# @date 29/05/2015
# @author Cindy Williams
#
# Checks an attribute field for duplicate values,
# and displays them along with the amount of duplicates.
#
# For use in the Python window in ArcMap.
#

import arcpy

mxd = arcpy.mapping.MapDocument("CURRENT")
lyrs = arcpy.mapping.ListLayers(mxd)

def checkDuplicate(ftr, field):
	vals = [row[0] for row in arcpy.da.SearchCursor(ftr, field)]
	dct = {x:vals.count(x) for x in vals}
	print ftr.name
	for k, v in dct.iteritems():
		if v > 1:
			print k, v

for lyr in lyrs:
	field_name = arcpy.ListFields(lyr, "*_ID")[0].name
	checkDuplicate(lyr, field_name)