用python如何实现学生成绩管理系统？

class Node(object):
 def __init__(self, data, pointer):
 self.data = data
 self.next = pointer


# 创建单链表
class SingleLinkedList(object):
 def __init__(self):
 self.head = Node(None, None)
 self.point = self.head

 def append(self, data):
 # 末尾追加节点
 new_node = Node(data, None)
 self.point.next = new_node
 self.point = new_node

 def insert(self, data, find):
 # 插入数据(前向插入数据)
 if not self.head.next:
  print(&＃39;链表为空&＃39;)
  return None
 new_node = Node(data, None)
 self.point = self.head
 while self.point.next.data != find:
  self.point = self.point.next
  if self.point.next is None:
  print(&＃39;没有找到该元素&＃39;)
  return None

 new_node.next = self.point.next
 self.point.next = new_node

 def delete(self, find):
 # 删除节点
 # 空链表
 if not self.head.next:
  print(&＃39;链表为空&＃39;)
  return None
 self.point = self.head
 while self.point.next.data != find:
  self.point = self.point.next
 pointer = self.point.next
 self.point.next = self.point.next.next
 del pointer

 def insert_after_head(self, data):

 node = Node(data, None)
 # bug 产生没写 if 返回
 if not self.head.next:
  self.head.next = node
  return None
 node.next = self.head.next
 self.head.next = node

 def reverse(self):
 local_list = SingleLinkedList()
 self.point = self.head
 count = 0
 while self.point.next:
  count += 1
  self.point = self.point.next
  data = self.point.data
  local_list.insert_after_head(data)
 return local_list

 def get_size(self):
 count = 0
 self.point = self.head
 while self.point.next:
  self.point = self.point.next
  count += 1
 return count

 def delete_by_tail(self, num):
 size = self.get_size()
 assert (num <= size)
 assert (num > 0)
 pos = size - num
 count = 0
 self.point = self.head
 while count  self.point.next.data:
   temp = self.point.data
   self.point.data = self.point.next.data
   self.point.next.data = temp
  self.point = self.point.next
  j += 1
  flag = 0
  if flag:
  break
  i += 1
  j = 0

 def print(self):
 # 打印结点
 self.point = self.head
 while self.point.next:
  self.point = self.point.next
  print(&＃39;{} ->&＃39;.format(self.point.data), end=&＃39; &＃39;)
 print(&＃39;&＃39;)


class StudentControlSystem(SingleLinkedList):
 # 打印菜单
 def print_menu(self):
 print(&＃39;*&＃39; * 30)
 print(&＃39;-&＃39; * 13 + &＃39;菜单&＃39; + &＃39;-&＃39; * 13)
 print(&＃39;1.增加学生信息&＃39;)
 print(&＃39;2.删除学生信息&＃39;)
 print(&＃39;3.修改学生信息&＃39;)
 print(&＃39;4.查找学生信息&＃39;)
 print(&＃39;5.显示所有信息&＃39;)
 print(&＃39;6.排序&＃39;)
 print(&＃39;0.退出程序&＃39;)
 print(&＃39;*&＃39; * 30)

 # 用户输入
 def user_input(self, item):
 try:
  item = int(item)
 except:
  pass
 # 增加信息
 if item == 1:
  self.add_info()
 # 删除信息
 elif item == 2:
  find = input(&＃39;请输入删除的学号：&＃39;)
  self.del_info(find=find)
 # 修改信息
 elif item == 3:
  self.modify_info()
 # 查找信息
 elif item == 4:
  self.search_info()
 # 显示信息
 elif item == 5:
  self.display_info()
 # 信息排序
 elif item == 6:
  self.rank_info()
 # 退出程序 保存数据
 elif item == 0:
  with open(&＃39;database.txt&＃39;, &＃39;w&＃39;) as f:
  self.point = self.head
  while self.point.next:
   self.point = self.point.next
   f.writelines(&＃39;{}\n&＃39;.format(self.point.data))
  exit()
 else:
  print(&＃39;请输入正确的数字&＃39;)

 # id 保证互异性
 def unique_id(self, std_id):
 self.point = self.head
 while self.point.next:
  self.point = self.point.next
  if self.point.data[&＃39;id&＃39;] == std_id:
  return False
 return True

 # 增加信息
 def add_info(self):
 # id 不能重复
 # 成绩不能超出范围
 name = input(&＃39;姓名：&＃39;)
 std_id = input(&＃39;学生id：&＃39;)
 while not self.unique_id(std_id=std_id):
  print(&＃39;id重复&＃39;)
  std_id = input(&＃39;学生id：&＃39;)
 grade = input(&＃39;学生成绩：&＃39;)
 if eval(grade) <0 or eval(grade) > 100:
  print(&＃39;超出范围&＃39;)
  grade = input(&＃39;学生成绩：&＃39;)
 print(name, std_id, grade)
 print(&＃39;请确认无误后保存&＃39;)
 choice = input(&＃39;y/n&＃39;)
 items = [&＃39;y&＃39;, &＃39;yes&＃39;, &＃39;Y&＃39;, &＃39;Yes&＃39;]
 if choice in items:
  print(choice)
  data = {&＃39;id&＃39;: std_id, &＃39;name&＃39;: name, &＃39;grade&＃39;: grade}
  self.append(data)

 # 删除信息
 def del_info(self, find):
 print(&＃39;请确认无误后保存&＃39;)
 choice = input(&＃39;y/n&＃39;)
 items = [&＃39;y&＃39;, &＃39;yes&＃39;, &＃39;Y&＃39;, &＃39;Yes&＃39;]
 if choice in items:
  if not self.head.next:
  print(&＃39;链表为空&＃39;)
  return None
  self.point = self.head
  while self.point.next.data[&＃39;id&＃39;] != find:
  self.point = self.point.next
  pointer = self.point.next
  self.point.next = self.point.next.next
  del pointer

 # 序列逆序
 def reverse(self):
 local_list = StudentControlSystem()
 self.point = self.head
 count = 0
 while self.point.next:
  count += 1
  self.point = self.point.next
  data = self.point.data
  local_list.insert_after_head(data)
 return local_list

 # 序列排序
 def sort(self, item):
 length = self.get_size()
 i, j = 0, 0
 flag = 1
 while i  int(self.point.next.data[item]):
   # self.point.data, self.point.next.data =
   # self.point.next.data, self.point.data
   temp = self.point.data
   self.point.data = self.point.next.data
   self.point.next.data = temp
  self.point = self.point.next
  j += 1
  flag = 0
  if flag:
  break
  i += 1
  j = 0

 # 修改信息
 def modify_info(self):
 find = input(&＃39;输入需要修改的学生的id：&＃39;)
 if not self.head.next:
  print(&＃39;链表为空&＃39;)
  return None
 self.point = self.head
 while str(self.point.next.data[&＃39;id&＃39;]) != find:
  self.point = self.point.next
  if self.point.next is None:
  print(&＃39;没有找到该元素&＃39;)
  return None
 name = input(&＃39;姓名：&＃39;)
 grade = input(&＃39;学生成绩：&＃39;)
 self.point.next.data[&＃39;name&＃39;] = name
 self.point.next.data[&＃39;grade&＃39;] = grade

 # 搜索信息
 def search_info(self):
 find = input(&＃39;输入需要查找的学生的id：&＃39;)
 if not self.head.next:
  print(&＃39;链表为空&＃39;)
  return None
 self.point = self.head
 while str(self.point.next.data[&＃39;id&＃39;]) != find:
  self.point = self.point.next
  if self.point.next is None:
  print(&＃39;没有找到该元素&＃39;)
  return None
 data = self.point.next.data
 print(&＃39;ID 姓名 成绩&＃39;)
 print(&＃39;{} {} {}&＃39;.format(data[&＃39;id&＃39;], data[&＃39;name&＃39;], data[&＃39;grade&＃39;]))

 # 信息排序
 def rank_info(self):
 choice = input(&＃39;1.成绩排序 2.学号排序：&＃39;)
 order = input(&＃39;1.升序 2.降序：&＃39;)
 if choice == &＃39;1&＃39;:
  item = &＃39;grade&＃39;
 elif choice == &＃39;2&＃39;:
  item = &＃39;id&＃39;
 else:
  return None
 self.sort(item=item)
 if order == &＃39;2&＃39;:
  temp = self.reverse()
  temp.display_info()
  return None
 self.display_info()

 # 显示信息
 def display_info(self):
 self.point = self.head
 print(&＃39;ID 姓名 成绩&＃39;)
 while self.point.next:
  self.point = self.point.next
  data = self.point.data
  print(&＃39;{} {} {}&＃39;.format(data[&＃39;id&＃39;], data[&＃39;name&＃39;], data[&＃39;grade&＃39;]))
 print(&＃39;&＃39;)


def main():
 SCS = StudentControlSystem()
 try:
 with open(&＃39;database.txt&＃39;, &＃39;r&＃39;) as f:
  for data in f.readlines():
  SCS.append(eval(data))
 except:
 with open(&＃39;database.txt&＃39;, &＃39;w&＃39;) as f:
  pass

 while True:
 SCS.print_menu()
 item = input(&＃39;请输入你的选择：&＃39;)
 SCS.user_input(item)


if __name__ == "__main__":
 main()