arcpy - Use Python to Find duplicate values in a feature Class and populate a field

So I found this python script on another post here and was trying to adjust it for my needs. I'm a very novice python user so I'm struggling with how to modify the script. I have a Feature Class stored in a feature Dataset that I want to search a field for duplicate values and populate a new field with Y for duplicate or N for none. The below script is what I found that looks like it will work once I find a way to drill down into my file geodatabase.

        from arcpy import *

        inShapefile = pointsShapefile

        checkField = "xyCombine"
        updateField = "dplicate"


       #List of values found once
        occursOnce = []
       #list of values found twice
        occursTwice = []

     cursor = da.SearchCursor (inShapefile, [checkField])
          for row in cursor:
          #Check value is not null
       if row[0]:
    #If not already found to occur twice, proceed

    if not row[0] in occursTwice:
        #If hasn't occured once yet
        if not row[0] in occursOnce:
            #Add to occurs once list
            occursOnce.append (row[0])
        #If value has already been found once
        else:
            #Add to occurs twice list (duplicates)
            occursTwice.append (row[0])
    del cursor


     cursor = da.UpdateCursor (inShapefile, [checkField, updateField])
     for row in cursor:
      #Check value is not null
        if row[0]:
           #check if value in occursTwice list (i.e. is duplicate)
    if row[0] in occursTwice:
        row[1] = "Y"
    else:
        row[1] = "N"

    cursor.updateRow(row)
   del cursor

Answer

Something like this should work:

import arcpy

inShapefile = pointsShapefile
checkField = "xyCombine"
updateField = "dplicate"


with arcpy.da.SearchCursor(inShapefile, [checkField]) as rows:
    values = [r[0] for r in rows]

d = {}
for item in set(values):
    if values.count(item) > 1:
        d[item] = 'Y'
    else:
        d[item] = 'N'


with arcpy.da.UpdateCursor(inShapefile, [checkField, updateField]) as rows:
    for row in rows:
        if row[0] in d:
            row[1] = d[row[0]]
            rows.updateRow(row)

And as @mr.adam suggested, the dictionary is not needed. here is the cleaner version:

import arcpy

def findDupes(inShapefile, checkField, updateField):

    with arcpy.da.SearchCursor(inShapefile, [checkField]) as rows:
        values = [r[0] for r in rows]

    with arcpy.da.UpdateCursor(inShapefile, [checkField, updateField]) as rows:
        for row in rows:
            if values.count(row[0]) > 1:
                row[1] = 'Y'
            else:
                row[1] = 'N'
            rows.updateRow(row)


if __name__ == '__main__':
    fc = r'C:\TEMP\crm_test.gdb\test'
    fld = 'Project_Manager'
    up = 'duplicates'

    findDupes(fc, fld, up)