input: Write a python function to compute the frequency of each element in a list.
  assert compute_frequency([1, 2, 3, 2, 1, 3]) == {1: 2, 2: 2, 3: 2}
  assert compute_frequency([4, 4, 4, 5, 5, 6]) == {4: 3, 5: 2, 6: 1}
  assert compute_frequency([10, 20, 10, 30, 20, 30, 30]) == {10: 2, 20: 2, 30: 3}
output: def compute_frequency(lst):
      frequency_dict = {}
      for item in lst:
          if item in frequency_dict:
              frequency_dict[item] += 1
          else:
              frequency_dict[item] = 1
      return frequency_dict