input: Write a function to return a new list containing only the 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([1, 1, 2, 2, 3], [2, 2, 3, 3, 4]) == [2, 2, 3]
  assert common_elements([], [1, 2, 3]) == []
  assert common_elements([1, 2, 3], []) == []
  assert common_elements([], []) == []
output: def common_elements(list1, list2): 
      common_list=[]
      for element in list1: 
          if element in list2: 
              common_list.append(element) 
      return common_list