input: def common_elements(list1: List[int], list2: List[int]) -> List[int]:
      """Find common elements between two lists and return them as a new list.
      >>> common_elements([1, 2, 3, 4, 8], [2, 6, 8, 10])
      [2, 8]
      >>> common_elements([1, 3, 5, 7], [2, 4, 6, 8])
      []
      """
output:     common = []
      for elem in list1:
          if elem in list2:
              common.append(elem)
      return common