input: Write a function to return a list of common elements between two given lists.
  def common_elements(list1, list2):
      common_list = []
      for element in list1:
          if element in list2:
              common_list.append(element)
      return common_list
  
  assert common_elements([1, 2, 3, 4, 8], [2, 6, 8, 10])==[2, 8]
  assert common_elements([5, 6, 7], [7, 8, 9])==[7]
  assert common_elements([1, 2, 3], [4, 5, 6])==[]
  assert common_elements([], [1, 2, 3])==[]
  assert common_elements([1, 2, 3], [])==[]
output: def common_elements(list1, list2):
      common_list = []
      for element in list1:
          if element in list2:
              common_list.append(element)
      return common_list