input: Write a python function to find the symmetric difference between two lists.
  assert symmetric_difference([1, 3, 4, 5], [2, 4, 6, 8])==[1, 3, 6, 8]
  assert symmetric_difference([10, 20, 30], [30, 40, 50])==[10, 20, 40, 50]
  assert symmetric_difference([1, 2, 3], [1, 2, 3])==[]
output: def symmetric_difference(list1, list2):
      set1 = set(list1)
      set2 = set(list2)
      sym_diff = set1.symmetric_difference(set2)
      return list(sym_diff)