input: Write a python function to identify duplicate items in a list using a set.
  assert identify_duplicates([1, 2, 3, 4, 5, 1, 2])==[1, 2]
  assert identify_duplicates([10, 20, 30, 10, 40, 50, 20])==[10, 20]
  assert identify_duplicates([7, 8, 9, 10])==[]
output: def identify_duplicates(lst):
      seen = set()
      duplicates = set()
      for item in lst:
          if item in seen:
              duplicates.add(item)
          else:
              seen.add(item)
      return list(duplicates)