input: 
  def common_elements(list1, list2):
      """ Returns a new list containing only the common elements between list1 and list2.
      >>> common_elements([1, 2, 3, 4, 8], [2, 6, 8, 10])
      [2, 8]
      >>> common_elements(['apple', 'banana', 'cherry'], ['banana', 'cherry', 'date'])
      ['banana', 'cherry']
      """
      common_list = []
      for element in list1:
          if element in list2:
              common_list.append(element)
      return common_list
  
output:     common_list = []
      for element in list1:
          if element in list2:
              common_list.append(element)
      return common_list