old_contents: # -*- coding: utf-8 -*-
  # Author Frank Hu
  # iDoulist Function 1 - process
  
  # copy a list into a new list, implement function 0 
  def copy(input_list):
  	new_list = input_list
  	return new_list
  
  # combine two list
  def combine(list1, list2):
      list_combine = list1
      # 测试发现列表赋值传递的是指针! 使用这行代码会导致 list1 的值在函数运行后发生变化
      for i in list2:
          list_combine.append(i)
      remove_duplicate_element(list_combine) #注意这里我重用了已有的轮子(去重函数)
      return list_combine
  
  def remove_duplicate_element(list):
      i = 0
      while i <= len(list) - 1:
          j = i + 1
          while j <= len(list) - 1:
              if list[i] == list[j]:
                  del list[j]
              j += 1
          i += 1
  
  # common elements in two list
  def common(list1,list2):
      list_common = []
      for i in list1:
          for j in list2:
              if j == i:
                  list_common.append(j)
      return list_common
new_contents: # -*- coding: utf-8 -*-
  # Author Frank Hu
  # iDoulist Function 1 - process
  
  # copy a list into a new list, implement function 0 
  def copy(input_list):
  	new_list = input_list
  	return new_list
  
  # combine two list
  def combine(list1, list2):
      list_combine = []
      for i in list1:
          list_combine.append(i)
      for i in list2:
          list_combine.append(i)
      remove_duplicate_element(list_combine) #注意这里我重用了已有的轮子(去重函数)
      return list_combine
  
  def remove_duplicate_element(list):
      i = 0
      while i <= len(list) - 1:
          j = i + 1
          while j <= len(list) - 1:
              if list[i] == list[j]:
                  del list[j]
              j += 1
          i += 1
  
  # common elements in two list
  def common(list1,list2):
      list_common = []
      for i in list1:
          for j in list2:
              if j == i:
                  list_common.append(j)
      return list_common
subject: revise combine function, list pointer issue